closed circuit television camera installation and networking

7/24/2019 Closed Circuit Television Camera Installation and Networking

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CHAPTER 1

INTRODUCTION

PROJECT BACKGROUND

CCTV is the acronym of Closed-circuit television (CCTV). Surveillance CCTV is one

of the most important evidence when deals with wrong doings. A video surveillance

system covering a large office building or a busy airport can apply hundreds and even

thousands of cameras. To avoid communication bottlenecs! the ac"uired video is

often compressed by a local processor within the camera! or at a nearby video server.

The compressed video is then transmitted to a central facility for storage and display.

#ased on the current technologies! with the set of personal computer ($C) and the

internet connection either wire or wireless! the monitoring can be done. %ith this! the

user may monitor the video wherever they want! and the random video playbac

functions can be provided. %ith these fle&ibilities! it gives more advantage to the user

to monitor and ensure the safety place they want. 't is also may increase the safety of

the user properties this is because there is image processing techni"ue apply in the

system.

This proect introduces the main components that can go to mae up CCTV systems

of varying comple&ity. CCTV (closed-circuit television) is a TV system in which

signals are not publicly distributed but are monitored! primarily for surveillance and

security purposes. CCTV relies on strategic placement of cameras and private

observation of the camera*s input on monitors. The system is called +closed-circuit+

because the cameras! monitors and,or video recorders communicate across a

proprietary coa&ial cable run or wireless communication lin. Access to data

transmissions is limited by design. lder CCTV systems used small! low-resolution

blac and white monitors with no interactive capabilities. odern CCTV displays can

be high-resolution color! providing the CCTV administrator with the ability to /oom

in on an image or trac something (or someone).

Tal CCTV allows the administrator to spea to people within range of the camera*s

associated speaers. CCTV is commonly used for a variety of purposes! including0

• 1otels.

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• Airports

• Shopping alls.

• 2oads and 1ighway

• 3ewelers Shops

• #ans

• oney 4&changes

• 2esidential Apartments

• aintaining perimeter security.

• onitoring traffic.

•

btaining a visual record of human activity.

The Applications for CCTV

$robably the most widely nown use of CCTV is in security systems and such

applications as retail shops! bans! government establishments! etc. The true scope for

applications is almost unlimited. Some e&amples are listed below.

onitoring traffic on a bridge.

2ecording the inside of a baing oven to find the cause of problems.

A temporary system to carry out a traffic survey in a town centre.

Time lapse recording for the animation of plasticine puppets.

5sed by the stage manager of a show to see obscured parts of a set.

The well-publicised use at football stadiums.

1idden in buses to control vandalism.

2ecording the birth of a gorilla at a /oo.

aing a wildlife program using a large model helicopter.

2eproducing the infrared vision of a goldfish6

Aerial photography from a hot air balloon.

$roduction control in a factory.

The list is almost endless and only limited by the imagination.

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The Camera

The starting point for any CCTV system must be the camera. The camera creates the

picture that will be transmitted to the control position. Apart from special designs

CCTV cameras are not fitted with a lens. The lens must be provided separately and

screwed onto the front of the camera. There is a standard screw thread for CCTV

cameras! although there are different types of lens mounts.

7iagram 8 Camera and 9ens

:ot all lenses have focus and iris adustment. ost have iris adustment. Some very

wide angle lenses do not have a focus ring. The *#:C* plug is for connecting the

coa&ial video cable. 9ine powered cameras do not have the mains cable. $ower is provided via the coa&ial cable.

The Monitor

The picture created by the camera needs to be reproduced at the control position. A

CCTV monitor is virtually the same as a television receiver e&cept that it does not

have the tuning circuits.

7iagram ; CCTV onitor

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Simple CCTV Systems

The simplest system is a camera connected directly to a monitor by a coa&ial cable

with the power for the camera being provided from the monitor. This is nown as a

line powered camera. 7iagram < shows such a system. $robably the earliest well-

nown version of this was the $ye bservation System that popularised the concept

of CCTV! mainly in retail establishments. 't was an affordable! do-it-yourself! self-

contained system.

7iagram < A #asic 9ine $owered CCTV System

The ne&t development was to incorporate the outputs from four cameras into the

monitor. These could be set to se"uence automatically through the cameras or any

camera could be held selectively. 7iagram = shows a typical arrangement of such a

system. There was even a microphone built into the camera to carry sound and a

speaer in the monitor.

The speaer! of course! only put out the sound of the selected camera. There were

however a few disadvantages with the system! although this is not to disparage it. The

microphone! being in the camera! tended to pic up sound close to it and not at the

area at which it was aimed. There was a noticeable! and sometimes annoying! pause

between pictures when switching. This was because the camera was powered down

when not selected and it too time for the tube to heat up again. The system was!

though! cheap to buy and simple to install. 't came complete in a bo& with camera!

8>mm lens! bracet! switching monitor and 8; metres of coa&ial cable with fitted

plugs. An outlet socet for a video recorder was provided! although reviewing could

be a little tedious when the cameras had been set to se"uence. There are now many

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systems of line powered cameras on the maret that are more sophisticated than this

basic system. ost of the drawbacs mentioned have been overcome. Cameras had

been around for a long time of course! before this development. The e&ample is given

to show the simplest! practical application. The use of some line powered cameras can

impose limitations on system design. They do though! offer the advantage of ease of

installation.

7iagram = A ?our-Camera 9ine $owered CCTV System

Mains Powered CCTV Systems

The basic CCTV installation is shown in diagram @ where the camera is mains

powered as is the monitor. A coa&ial cable carries the video signal from the camera to

the monitor. Although simple to install it should be born in mind that the installation

must comply with the relevant regulations such as the 'nstitute of 4lectrical 4ngineers

latest edition. (:ow incorporated into #ritish Standard #S>8). ?ailure to do so

could be dangerous and create problems with the validity of insurance. This

arrangement allows for a great deal more fle&ibility in designing comple& systems.

%hen more than one camera is re"uired! then a video switcher must be included as

shown in diagram >. 5sing this switcher any camera may be selected to be held on the

screen or it can be set to se"uence in turn through all the cameras. 5sually the time

that each camera is shown may be adusted by a control nob or by a screwdriver.

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7iagram @ A #asic ains $owered CCTV System

7iagram.> A ?our-Camera System %ith Video Switcher

Systems with Video Recording

The ne&t development of a basic system is to add a video recorder! the arrangement

would be as shown in diagram .

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7iagram A ulti Camera System %ith Video 2ecorder

%ith this arrangement the pictures shown during play bac will be according to the

way in which the switcher was set up when recording. That is! if it was set to

se"uence then the same views will be displayed on the monitor. There is no control

over what can be displayed.

Movable Cameras

So far all the cameras shown have been fi&ed with fi&ed focal length lenses. 'n many

applications the area to be covered would need many fi&ed cameras. The solution to

this is to use cameras fi&ed to a movable platform. This platform can then be

controlled from a remote location. The platform may simply rotate in a hori/ontal

plane and is generally nown as a scanner. Alternatively the platform may be

controllable in both hori/ontal and vertical planes and is generally nown as a pan! tilt

unit. A basic system is illustrated in diagram B. This chapter does not deal with how

cameras are controlled or wired it is ust showing the facilities that may be

incorporated into a CCTV system. Therefore the diagrams that follow are simply

descriptive bloc diagrams and not connection drawings.

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7iagram B #asic ovable Camera System

Cameras may be used indoors or outdoors. %hen used outdoors they will always

re"uire a protective housing. ?or indoor use the environment or aesthetic constraints

will dictate whether a housing is needed. Systems may contain a combination of both

fi&ed and movable cameras.

7iagram ultiple Camera System

Other Considerations

This has been an introduction to some of the fundamentals of CCTV. 2ecent

developments have made some very sophisticated systems possible. These include

concepts such as multiple recording of many cameras almost real time pictures over

telephone lines true real time colour pictures over the 'S7: telephone lines

switching of hundreds! even thousands! of cameras from many separate control

positions to do/ens of monitors reliable detection of movement by electronic

evaluation of the video signal immediate full colour prints in seconds from a camera

or recording the replacement of manual controls by simply touching a screen.

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1. FUNDAMENTALS OF VIDEO

Video signals are the signals used to send closed circuit television pictures from one

place to another. Television (TV) is literally! tele-vision! a means of viewing one place

from somewhere else. The word video comes from the 9atin verb Videre! to see. A

television picture is made up from a number of hori/ontal lines on the television

screen! which are laid down! or scanned! from the top to the bottom of the television

screen. There are now only two standards for TV pictures in general use! @;@ lines in

the 5SA (4'A) and 3apan and >;@ lines elsewhere (CC'2). The descriptions thatfollow are based on the >;@-line system. The number of lines describes how each still

picture is created! but a television picture is made up from a number of still pictures

displayed every second. There is a characteristic of the human eye nown as

Dpersistence of vision.E The eye retains an impression of an image for a fraction of a

second after it has disappeared. 'f a series of still images is presented at a rate of about

8= per second an impression of continuous movement will be perceived. This!

however! would give rise to a very distracting flicer. 'f the rate were increased to ;=

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images per second! the flicer would be almost unnoticeable. 'ncreasing this to @F

images per second would eliminate noticeable flicer.

To transmit @F complete images per second would be needlessly comple& and

e&pensive to produce. The solution is to adopt what is nown as interlaced scanning.

'nstead of scanning the full >;@ lines @F times a second! the scanning speed is

effectively doubled and so is the vertical spacing of the lines. Therefore! one scan

produces <8; 8,; lines from the top to the bottom of the picture. This is nown as

one field. The ne&t scan is arranged to start at a precise position e&actly between the

lines of the first scan! so that the lines of the second field interlace! lie fingers!

between the lines of the first field. 'n this way! a complete frame of video is created

made up from two fields.

n a TV screen! the phosphor on the screen continues to glow from the first scan

while the second scan is being displayed. 'n this way! although only ;@ complete

pictures (frames) are presented per second the screen is scanned @F times (fields) per

second. The result is to achieve a flicer rate of @F 1/ (cycles per second) while only

using a bandwidth for ;@ frames per second. Some broadcast televisions now use a

techni"ue called G8FF1/ technologyH to further reduce the flicer on the TV screen.

1owever! this techni"ue is not generally used in CCTV monitors due to the e&tra cost

involved.

7iagram ;.8 'nterlaced ?ields

The relationship between the length of the hori/ontal lines and the height of the

picture is always the same and is nown as the aspect ratio. 't is given by the

following ratio.

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Monochrome Video Signal Components

The signal used to carry the scanning pictures from one place to another is called the

video signal. A voltage is generated proportional to the brightness of the image at any

point on a hori/ontal line. ?or the brightest parts! corresponding to a white area! a

level of one volt is produced this is the !ite le"el. ?or the darest parts

corresponding to a blac image! a voltage of appro&imately F.< volts is produced this

is the #lac$ le"el. #etween these levels! the camera will produce a voltage

proportional to the shade of grey of the image.

1owever! the brightness signal is not the only part of the video signal normally

produced by a camera. Some method is re"uired of synchronising the monitor on

which the camera picture is being displayed to the field and line scanning process.

This is to enable it to re-create the picture that the camera is viewing. The method

used to achieve this is to add pulses for the start of each field and the start of each

line. The synchronising! or sync! pulses for the start of each field are called %ertical

&'nc P(lses. These vertical sync pulses reduce the voltage from the blac level down

to /ero voltsand tae up a time space e"uivalent to ;@ hori/ontal lins! i.e. 8.>

milliseconds. The sync pulses for the start of each line are called H)ri*)ntal &'nc

P(lses. The hori/ontal sync pulses are also from the blac level down to /ero volts

and are =. microseconds in long.

The type of video signal that contains both video and synchronising information is

nown as composite video.

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7iagram ;.; composite video signal

The relationship in level between the video signal and sync pulses is normally given

by the following formula0

The complete hori/ontal line lasts >= microseconds. There is a short period between

the end of the video signal for a line and the leading edge of the ne&t hori/ontal sync

pulse. This is nown as the fr)nt +)rc!. There is also a short period between the

trailing edge of the hori/ontal sync pulse and the start of the video signal of the ne&t

line. This is nown as the #ac$ +)rc!. Considering the times for the hori/ontal sync

and the front and bac porches! the actual length of the video signal in a hori/ontal

line is @; microseconds. 'n practice only = to @F microseconds is visible due to over-

scanning at the monitor.

There is not ust one sync pulse. The nominally >;@ line system uses ;@ lines for field

blaning! therefore @F lines in one frame. This leaves @@ lines for picture

information. The ;@ lines are used as follows0

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2. CAMEAS

ntrod!ction

The principal part of a CCTV system is the camera. There are many types of camera

and many ways in which they are used. 'n this chapter! the different sorts of cameras

and the fundamentals of their operation will be e&amined. 't will also e&plain the

terms describing the performance of the cameras. This will enable an understanding of

the data sheets available for the myriad of cameras available on the maret. There is

now no standard method for manufacturers to present data defining camera

performance. Therefore! their literature should be studied carefully before maing a

selection and comparisons made against a common standard.

Types of Cameras

nternal Cameras

'nternal cameras are usually designated for use indoor without the need for

environmental protection. :ormally the cameras are simply fitted with a lens to view

the re"uired area and mounted on a wall or ceiling bracet. 'f the camera is in an area

such as a corridor or other place where the light level doesnEt change! then a simple

manual iris lens may be used. The light level may change because there are windows

or sylights in the area being viewed. Alternatively! if twenty-four hour operation of

the camera is needed then an automatic iris lens or another means of electronic

sensitivity control must be used. (See electronic shutter cameras.). ?re"uently the

styling of an internal camera is important because an architect or similar person willwant the camera to blend into the surrounding decor. 'n those cases! the camera may

be mounted inside some ind of housing. There are many housings of different styles

available! from simple cases through to domes! wedges and other types. 'nternal

housings are also used for other reasons. 't may be important that the camera is not

seen at all! in which event a covert housing is used to hide the camera or disguise it as

something else. 1ousings may also be used to give a measure of protection in certain

situations. There are many types of enclosures that can be used to protect the camera

from vandalism! dust! or other contaminants.

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"#ternal Cameras

4&ternal cameras are usually described for use in outdoor situations. They are nearly

always housed in some form of weatherproof housing! an e&ception being where the

camera case itself is water-resistant. The e&ternal camera housing normally contains a

heater and thermostat to prevent the glass window at the front from misting at low

temperatures. 4&ternal cameras always need some form of electronic sensitivity

control. This is because! over the course of the day and night! the light level may well

change by a factor of over a million times. At the time this boo went to press the

most effective way of giving such electronic sensitivity control is an automatic iris

lens fitted with a neutral density spot filter. Chapters = and 8= provide more detailed

information on lenses and lighting.

"lectronic Sh!tter Cameras

There are an increasing number of cameras being introduced with Delectronic

shuttersE electronic devices that are controlled by the amount of light falling on the

imaging device. 'n effect! it is the electronic e"uivalent of the variable speed

mechanical shutter fitted to early cine cameras. 'n these! the amount of light was

measured by a photoelectric cell! an increase in light causing the shutter to revolve

faster and vice versa. The same problems apply to both devices. At very high light

levels! there is a limit to the speed at which the shutter can effectively operate without

the picture flaring. At very low light levels! the e&posure time is so long that moving

images become blurred. Some manufactures have claimed that these cameras

eliminate the need for an automatic iris lens. This is doubtful in all conditions. Theyare ideal for indoor conditions where there is a limited range of light levels. As

always! the manufacturerEs specification should be consulted carefully to chec the

light range covered. Another problem that should be appreciated is that because the

iris is invariably set at the ma&imum aperture the depth of field is greatly reduced. See

automatic light control and electronic shutter later in this chapter.

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Miniat!re Cameras

Since CC7 cameras (see later in this chapter) have been available! the si/e of cameras

has reduced considerably. These miniature cameras are available in a number of styles

in two main groups! either where the camera is a complete unit or where the image

sensor is separated from the camera electronics. Complete cameras are available at the

present time with dimensions similar to the si/e! say! of a pac of cigarettes. 'f even

smaller si/es are re"uired! the cameras with separate sensor heads have sensor blocs

of only ;@mm cubed. ne restriction to the minimum si/e of camera is due to the

necessity of fitting a lens and mounting the camera. The ultimate is a camera of

current design that is about the si/e of a thumbnail! including all the electronics.

$ine Powered Cameras

:ormally a CCTV camera has to have some ind of power source! either wired from a

central point or from a local mains spur. bviously there is a cost involved of

providing the necessary cabling or supply points for such cameras. Some camera

manufacturers have addressed this issue by maing cameras to which the power for

the camera is sent down the same coa&ial cable used to bring the video signal bac

from the camera. CCTV systems using line-powered cameras! then! cost less to install

in terms of supply cables or mains spurs. There are! however! two disadvantages.

?irst! some cameras need a specialised power supply unit to feed the camera and

separate the video for the monitor. ?urthermore! with long cable runs it is not possible

to amplify the video signal from the camera because the power cannot travel through

the video amplifier. This is also a problem if there is ground loop interference on thecamera as it is not possible to use a video isolation transformer with line powered

cameras.

%oard Mo!nted Cameras

#oard mounted cameras are normally small CC7 cameras mounted on the printed

circuit board of another system. They are used to give a picture as part of the function

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of the system. The best e&ample of board mounted cameras is those used in video

entry phone systems. 'n these systems! a complete CC7 camera with a lens is

mounted on the $C# of the door entry unit. The board-mounted camera gives pictures

to residents! on small dedicated monitor units! of the person operating the bell push.

Types of mage Sensors

T!bed Cameras

The first CCTV cameras to be used were based around special vacuum tubes with a

light sensitive coating on one end. 9ight striing this coating caused electric current to

flow down the tube! proportional to the amount of light falling at each point on the

coating. The circuits of the camera then converted the current to the video signal.

This was a good initial design and gave cameras that had good sensitivity and

resolution. 1owever the cameras were buly and the tubes had a limited life span!

re"uiring regular! e&pensive tube changes. CC7 cameras! when introduced! were

smaller! lighter and re"uired practically no maintenance. This has led to their

widespread replacement of tubed cameras in CCTV systems! where CC7 cameras are

now used in practically all new installations. ?or this reason! no further discussion of

tubed cameras will be made in this report.

CC& Cameras

CC7 is an abbreviation of C!arge C)(+led De"ice. This is the name given to a

group of optical detector integrated circuits made from semiconductors (see diagram

<.8). A lens focuses light onto the surface of the CC7 image sensor. The areas of light

and dar are sensed by individual photo-diodes! which build up an electrical charge

proportional to the light. That is to say that the brighter the light on an individual

photo-diode the bigger the charge developed. These photo-diodes are arranged in a

matri& of rows and columns and are given the name picture cells or Pi,els. The

charge is removed from each pi&el by rows of CC7 cells. These CC7 rows are lie

ladders for charge! enabling step-by-step the charge on each pi&el! and conse"uently

the light level on it! to be read off by processing electronics.

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%hen the first CC7 cameras were developed! it was important that they could replace

e&isting tube cameras without having to change lens si/es. Therefore! the first CC7

cameras were created in ;,<H format. As CC7 sensor technology has improved! the

format of CC7 cameras has decreased to 8,; inch! 8,< inch! and most recently to 8,=

inch and 8,Bth inch to mae cameras smaller and cheaper. The associated lenses are

also much more compact! but not necessarily cheaper due to the much higher

accuracy re"uired to grind a smaller lens. The dimensions of the imaging devices are

shown in Chapter =.

7iagram <. 8 CC7 'maging 7evice

An amplifier is needed to boost the signal from the CC7 sensor electronics up to the

level where it can be used on a monitor. A synchronising generator is also used in the

CC7 camera to generate the signals that read the light level charge off the CC7 and

the synchronisation pulses used by the video monitor to re-create the image. The

mi&er section combines the video and synchronisation signals to produce the

composite video signal used by the monitor.

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7iagram <. ; onochrome CC7 Camera #loc 7iagram

There are many advantages of CC7 cameras that have led to their wide spread

replacement of tubed cameras. ?irst! CC7 cameras use less power and need no high

voltages lie the tube. As mentioned in the section on miniature cameras! CC7

cameras can be very much smaller than tubed cameras. The picture linearity is better

with CC7 cameras as tubed cameras used a magnetic field to scan the image sensor. 't

is e&tremely difficult to mae a magnetic field that is completely even over a given

area. This meant that the pictures from tubed cameras were sometimes distorted by

the magnetic field! bulging out at the edges (barrelling) in bulging in (pin-cushioning).

CC7 cameras do not use magnetic fields and conse"uently do not have this geometric

distortion. CC7 cameras are also a good deal more rugged than tube cameras.

Viewing the sun or another bright point could easily damage the surface of the tube

and the tubes regularly needed replacement as a routine maintenance tas. CC7

cameras do not have this problem and are not damaged by high light intensities! nor

do images become burned into the surface over long periods. This! and the ability of

CC7 cameras to survive vibration and mechanical shoc! gives very much reduced

maintenance cost for CC7 cameras.

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Colo!r CC& Cameras

Colour CC7 cameras are basically the same as monochrome cameras. 1owever! there

are additional components that have important effects on the performance of the

camera

7iagram <. < Colour CC7 Camera #loc 7iagram

9ight passes through the lens and through a colour correction filter on to the CC7.

The CC7 is sensitive to infrared light! which is present in normal daylight. This

infrared light produces false signals from the CC7 that affects the purity of the

colours reproduced by the camera. The colour correction filter removes the infrared

light before it hits the CC7 and ensures the colour purity of the camera. 1owever! it

also means that infrared illuminators cannot be used with normal colour cameras as

the colour correction filter removes all the lighting created. The actual CC7 image

sensor comprises of an array of pi&els lie a monochrome camera. 1owever! each

pi&el is subdivided in to three smaller light sensitive areas that are constructed to be

sensitive to red! green and blue light respectively. Conse"uently the pi&els are larger

in si/e than for monochrome CC7s and the number of pi&els which can be fitted on to

a colour CC7 of a given si/e is less than a monochrome CC7 of e"ual dimension.

This is why! generally! monochrome cameras still have resolution which is higher than

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colour cameras. The colour correction filter and colour sensitivity of the pi&els also

tend to mae colour cameras less sensitive to light that monochrome cameras.

Typically! colour cameras have sensitivities between 8 lu& and ;.@ lu& whereas

monochrome cameras have sensitivities between F.F8 lu& and F.8 lu&. The separate

brightness signals for red! green and blue are amplified separately and the used by

signal processing circuits to produce the luminance (I) signal (by combination as

described in chapter ;) and the chrominance (C) signal (by phase and amplitude

modulation of the =.=<=1/ colour sub-carrier as described in chapter ;). The I and

C signals are then combine with the composite sync pulses to produce a composite

colour video signal. any colour cameras also feature a separate connector where the

I and C signals are output separately for connection to Super V1S video recorders

and monitors! for improved resolution.

7iagram <. = 5sing I-C output with S-V1S recorder

Two coa&ial cables must be installed between the camera and the S-V1S video

recorder. The I-C output of the recorder must be connected to the I-C input of the

monitor. This is normally achieved using a pre-made S-V1S cable with mini-7':

connectors on each end. 1owever! the benefit of investing in this cabling plus an S-V1S recorder and high-resolution colour monitor (=FF TV9 at centre) will be

noticeably better live and playbac pictures in terms of resolution. 2esolution of

typically =FF TV9 will be possible when viewing live action pictures (compared with

about <@F TV9 using the composite video output of the camera). 2esolution of

typically =FFTV9 will be possible when viewing pictures recorded on theS-V1S

video recorder (compared with about ;=F TV9 compared with a standard V1S

recorder). The down side is the cost. An S-V1S system lie this may cost twice as

much as a standard V1S system using composite video.

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Advantages of CC& Cameras

:o geometric distortion.

:o coils! magnets! or glass tube.

:ot prone to ghosting or image burn.

ore compact and resistant to vibration.

:ot affected to electromagnetic interference.

'nitially CC7 cameras could not provide the same degree of resolution compared to

tubed cameras. The dynamic range was less and produced fewer shades of grey.

1owever! improvements in CC7 sensor design have meant that the current generation

of CC7 cameras produces e&cellent images of high resolution and accurate colour

reproduction.

&igital Signal Processing '&SP( CC& Cameras

'n conventional CC7 cameras the functions of amplification! signal processing and

mi&ing are carried out by analogue circuits! which wor on changing the voltages of

the signals by various means. Adustments to picture "uality are made by small

adustable resistors which are set up to give the best overall performance across a

range of camera operating conditions (light levels etc.) This approach is very cost

effective and gives good "uality pictures in most lighting conditions 1owever! these

adustments are! at best! a compromise and the effects of tolerances in the values of

the electronic components and changes over the lifetime of the camera can cause the

"uality of pictures obtained from the camera to vary greatly. 'n 7S$ cameras digital

circuits! as shown in figure <.@! carry out the signal processing and mi&ing.

The signals from the CC7 are connected to an analogue to digital converter (A7C).

This converts the brightness level from each point into a number. 'n this way! the

entire picture captured by the CC7 at any moment is represented by a group of

numbers. These numbers are processed at high speed by the digital signal processor!

which does mathematics on the numbers in order to produce the video signal at the

output of the camera. The digital signal processor gives the other name used for digital cameras! 7S$. The composite video signal or I-C video signal is produced by

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a digital to analogue converter (7AC) which taes the finished information from the

digital signal processor and produces the composite video described in chapter ;.

ost 7S$ cameras still produce these analogue composite video and I-C signals as

this is currently the most popular format re"uired by the other e"uipment in the video

system monitors! switchers! multiple&ers! VC2Es etc. 7S$ cameras do have the

possibility to produce the video signal in a digital form and it is liely that this will

become popular when a worldwide standard is agreed for sending video pictures

digitally in CCTV systems.

7iagram <. @ 7igital Colour CC7 Camera #loc 7iagram

A microprocessor controller sets the settings of the camera! controlled by the 7S$

circuits. This is a small computer built in to the camera! which controls the

mathematics used by the 7S$ circuits to build the video signal. The controls of the

camera are usually a series of push buttons on the camera! which are scanned by the

controller. %ith these buttons the user can select and adust the picture "uality and

performance of the camera using a series of menus overlaid on to the video picture by

the controller. bviously! the e&tra circuitry re"uired by a 7S$ camera mae them

more e&pensive than a conventional analogue camera. 1owever! there are a number of

benefits for this e&tra e&penditure in terms of features that are not available fromconventional analogue cameras. These include0

22 | P a g e



&ta#ilit' - the adustments to the camera are made by changing number values

on an on-screen menu and not by small screwdriver adustments.

Conse"uently the settings of the camera are easily repeatable and tend not to

change over time. -en( +r)gramming - provides an easy and rapid way to adust the camera

for the best picture during installation.

Digital *))m - The 7S$ circuits have a complete numerical model of each

picture and can manipulate these numbers. #y performing certain calculations!

the 7S$ circuits can selectively enlarge a section of the picture! producing a

/oomed-in image. This is a useful feature but it should be borne in mind that

the number of pi&els in the CC7 is constant and so the greater the amount of

digital /oom used! the poorer the apparent resolution of the picture will be.

-(lti.*)ne #ac$lig!t c)m+ensati)n - 5nlie analogue cameras! which

compensate for bright light behind an obect by sampling the video voltage

across the whole picture! 7S$ cameras and have a number of separate /ones

which can be positioned to cover bright light sources. Conse"uently! this

provides better overall picture "uality in these situations.

A(t)matic /(alit' ad0(stment - 7S$ cameras can hold a model of how a

good "uality video signal should appear. The 7S$ circuits can then compare

this with the picture being produced at any moment! and then actively adust

the camera to provide the optimum picture "uality. This can give very good

picture "uality over a very wide range of lighting conditions.

Rem)te set.(+ and c)ntr)l - lie any computer! the microprocessor controller

can communicate with other computers over a digital lin. Conse"uently! 7S$

cameras can be used in systems where they are set up and controlled by a

matri& switcher or a $C! even over great distances. This also simplifies camera

replacement in the field as when a camera becomes faulty the replacement

fitted can have identical settings downloaded very "uicly to give identical

performance to the original camera.

Twin Colo!r)Monochrome Cameras

Twin colour,monochrome cameras! are designed to meet a particular re"uirement in

CCTV systems. Sometimes! it is re"uired to have outdoor cameras which produce

colour images in the day but which can provide good "uality pictures in low light

23 | P a g e



levels at night! perhaps even using infrared illuminators. 'n the past! the only way to

meet this re"uirement was to use two separate cameras one monochrome! one colour

that were switched over automatically by some type of photocell or control system.

'mprovements in CC7 technology and the introduction of 7S$ cameras have led to

the availability of colour cameras which produce monochrome pictures at night and

which have good sensitivity to infrared illumination. The cameras wor as normal

colour cameras during the day. The night-time mode is controlled either by the camera

itself (by sampling the AJC voltage! see AJC below) or remotely by a control input.

'n the nighttime mode! the colour sub-carrier is switched off and the camera produces

ust the monochrome composite video signal. 7ual format cameras do have to

overcome the problem of the infrared cut filter. Colour cameras normally have an

ifrared cut filter that removes infrared light and ensures accurate colour reproduction

by the camera. 1owever! dual format cameras cannot use the colour correction filter

at night because this would filter out the light produced by infrared illuminators.

Camera manufacturers have solved this problem in two ways. ne way is to have

small motor that moves a colour correction filter in front of the CC7 in colour mode

but retracts it in monochrome mode. This has the advantage of ensuring the best

colour "uality but has the disadvantage that a comple& electro-mechanical assembly is

built in to the camera and this will lower itEs reliability compared with a camera that

has no moving parts. The other solution is to dispense with the colour correction filter

entirely. The effect of infrared light is then adusted by the digital signal processing of

the camera. This gives a camera! which is very reliable! but the colour reproduction of

the camera will always be a compromise as the amount of infra red light seen by the

camera constantly changes and the compensation in the digital signal processing is

fi&ed.

&igital Cameras

There are already several camcorders on the maret that produce a digital output

instead of an analogue video signal. These record onto a miniature 7AT (7igital

AudioTape) in digital form or download straight to codecs. The playbac can be either

via a digital to analogue converter in to a conventional monitor! or direct by 2J#

input to a computer monitor. The direct input into a computer monitor will provide a

24 | P a g e



significant improvement in resolution and colour rendering. The recording capability

for CCTV is still limited by the current problems of compression and storage capacity!

but this is advancing rapidly and soon will not be the main problem. 'magine

computer graphic type resolution and "uality in a CCTV installation! the day will

come. The maority of advances in CCTV cameras have been as a result of

developments in camera technology and miniaturisation in the vast domestic maret.

There is no reason to doubt that the digital camera technology will soon be available

to our industry! although not at the time of publication of this issue. 1owever! it

maes sense to propose some of the advantages of this technology when it becomes

readily available.

Transmission of video along telephone lines or fibre optic cable re"uires an analogue

to digital converter (A7C) to be incorporated in the transmitter and the reverse digital

to analogue converter (7AC) at the receiving end. 5sing a direct digital output from

the camera will render the A7C unnecessary! thus saving cost. %hen e"uipment is

available that can accept a digital signal then the 7AC will not be re"uired providing

further savings. 't will no longer to use coa&ial cable with all its problems of

connectors and limited range. 'nstead! simple twisted pair cables can be used with

greatly improved distances and "uality. ultiple&ers need to convert the analogue

signal to a digital signal to hold in the frame store again! this will be unnecessary.

4very time a conversion from one form of signal to another is rendered unnecessary!

there will be an improvement in resolution and picture "uality.

25 | P a g e



3. LENSES

ntrod!ction

The human eye is an incredibly adaptable device that can focus on distant obects and

immediately refocus on something close by. 't can loo into the distance or at a wide

angle nearby. 't can see in bright light or at dus! adusting automatically as it does so.

't also has a long Ddepth of fieldE therefore! scenes over a long distance can be in

focus simultaneously. 't sees colour when there is sufficient light! but switches to

monochrome vision when there is not. 't is also connected to a brain that has a faster

updating and retentive memory than any computer. Therefore! the eyes can swivel

from side to side and up and down! retaining a clear picture of what was scanned. The

brain accepts all the data and maes an immediate decision to move to a particular

image of interest! select the appropriate angle of view and refocus. The eye has

another clever tric in that it can view a scene of great contrast and adust only to the

part of it that is of interest.

#y contrast! the basic lens of a CCTV camera is an e&ceptionally crude device. 't can

only be focused on a single plane! everything before and after this plane becoming

progressively out of focus. The angle of view is fi&ed. At any time! it can only view a

specific area that must be predetermined. The iris opening is fi&ed for a particular

scene and is only responsive to global changes in light levels. 4ven an automatic iris

lens can be only be set for the overall light level! although there are compensations for

different contrasts within a scene. Another problem is that a lens may be set to see into

specific areas of interest when there is much contrast between these and the

surrounding areas. 1owever! as the sun and seasons change so do light areas become

26 | P a g e



dar and dar areas become light. The important scene can be Dwhited outE or too dar

to be of any use.

A controversial but important aspect of designing a successful CCTV system is the

correct selection of the lens. The problem is that the customer may have a totally

different perspective of what a lens can see compared to the reality. This is because

most people perceive what they want to view as they see it through their own eyes.

Topics such as identification of miscreants or number plates must be subects debated

fre"uently between installing companies and customers.

The selection of the most appropriate lens for each camera must fre"uently be a

compromise between the absolute re"uirements of the user and the practical use of thesystem. 't is ust not possible to see the whole of a large loading bay and read all the

vehicle number plates with one camera. The solution may be more cameras or

viewing ust a restricted area of particular interest. A Company putting forward the

system proposal should have no hesitation in pointing out the restrictions that may be

incurred according to the combination of lens versus the number of cameras. #etter

this than an unhappy customer who is reluctant to pay the invoice.

Although a lens is crude compared to the human eye! it incorporates a high degree of

technology and development. There can be a large variation in the "uality between

different maes and this should be considered according to the needs of a particular

installation. The lens is the first interface between the scene to be viewed and the

eventual picture on the monitor. Therefore! the "uality of the system will be very

much affected by the choice of lens. ?or general surveillance of! for instance! a small

retail shop! it is possible to use a lower "uality lens with "uite acceptable results. As

the demands of the system re"uirement increase then the use of a premium "uality

lens must be considered. The difference in cost between a poor "uality and a high

"uality lens will be a very small percentage of the total cost of a large industrial

system.

27 | P a g e



The CCTV $ens

"#pos!re Control

The e&posure in a normal photographic camera can be controlled by a combination of

shutter speed and iris opening. This is not so with a CCTV camera lens. A standard

CCTV camera produces a complete picture every 8,; of the mains fre"uency. This is

every 8,;@ second where the mains fre"uency is @F 1/ (cycles per second) and every

8,<F second where the mains fre"uency is >F 1/. Jenerally the e&posure time is fi&ed

and the only control of the amount of light passing to the imaging device is by

adusting the si/e of the iris. This is covered in more detail later in this chapter. ost

camera tubes and imaging devices have some tolerance of the amount of light passed

by the lens to create an acceptable picture. The range of tolerance is generally

inversely proportional to the sensitivity of the camera. The more sensitive cameras

re"uire greater control of the iris aperture.

Types of $enses

$ens *ormats

4arly CCTV lenses were designed for the 8H format tube camera and many of these

are still available on the maret. The lens screw thread on these cameras is called a C-

mount. This is a particular design of thread si/e and flange length originally used on

photographic cameras. 'n recent years lenses have been developed for the ;,<H! 8,;H

and now 8,<H format cameras. Conse"uently! great care must be e&ercised when

selecting a lens for a particular camera. 3ust as there are four formats of camera so

there are four formats of lenses and they are not compatible in every combination. A

lens designed for a larger format camera may be used on a smaller format but not the

reverse. 'n addition! the field of view will not be the same on different si/e cameras.

There is now a further complication in that there is a range of lenses with what is

called the CS-mount. The difference between the two types of mount is the flange

bac length! which is the distance from the bac flange of the lens to the face of the

sensor. See diagram =.8.

28 | P a g e



The screw thread and shoulder length for each type of mount is identical. This maes

it impossible to see the difference e&cept that the overall si/e of the CS-mount lens is

generally smaller. A C-mount lens may be used on a CS-mount camera with an

adapter ring but a CS-mount lens cannot be used on a C-mount camera. The main

problem is that either type of lens can be screwed onto both types of camera without

apparent damage. The result is that if the wrong type is used it will be impossible to

focus the camera. Some C-ount lenses have a proection at the bac that could

damage the sensor in a CS-ount camera.

7iagram =. 8 Types of 9ens ounts

A chart is provided at the end of this chapter showing the relationships between

different lenses and camera combinations and the associated angle of view. At the

time of going to press! most lenses with a focal length of ;@mm and above are still

designed for 8H cameras. This means that special care must be taen when using this

long focal length lens on modern cameras. ?or instance! a ;@mm 8H lens provides the

following appro&imate angles of view on the different formats. Therefore! there would

be a significant variation in the e&pected scene content if this fact were overlooed.

?2AT 8+ ;,<+ 8,;+ 8,<+

A:J94 ? V'4% ;K .@K 88=K .K

7iagram =. ; Angle of view for different formats

29 | P a g e



$ens Selection

There are two other main factors that must be considered when selecting the most

appropriate lens for a particular situation. The f)cal lengt! and the type of iris

c)ntr)l. %ithin each of these factors! there are other features that will also need to be

considered. 9enses may be obtained with all combinations of focal length and iris

control. The selection will depend on the site and system re"uirement.

*ocal $ength

The focal length of a lens determines the field of view at particular distances. This can

either be calculated from the formula given later in this chapter or found from tables

provided by most lens suppliers. ost manufacturers also provide simple to use slide

or rotary calculators that computes the lens focal length from the scene si/e and the

obect distance. The longer the focal length the narrower is the angle of view.

Although not strictly correct! lenses with a focal length longer than ;@mm are often

called /oom lenses. The focal length of the lens re"uires careful selection to ensure

that the correct area is in view and that the degree of detail is acceptable. A rule of

thumb is that to DseeE a person on a monitor they should represent at least 8FL of the

screen height. To DseeE in this conte&t means to be able to decide that it is a person.

?or purposes of being able to identify a nown person re"uires them to be at least

@FL of the screen height and preferably >FL. An unnown person should occupy at

least 8;FLof the screen height.

*i#ed *ocal $ength

This type of lens is sometimes called a monofocal lens. As the name implies! it is

specified when the precise field of view is fi&ed and will not need to be varied when

using the system. The angle of view can be obtained from the supplierEs specification

or charts provided. They are generally available in focal lengths from <.mm to

@mm. 9onger focal lengths may be produced by adding a ;& adapter between the

lens and the camera. 't should be noted that this would increase the f-number by a

factor of two (reducing the amount of light reaching the camera). 'f focal lengths

longer than these are re"uired! it will be necessary to use a /oom lens and set it

accordingly.

30 | P a g e



4&cept for very wide-angle lenses! other lenses have a ring for adusting the focus. 'n

addition! cameras include a focusing adustment that moves the imaging device

mechanically relative to the lens position. This is to allow for minor variations in the

bac focal length of lenses and manufacturing tolerances in assembling the device in

the camera. Correct focusing re"uires setting of both these adustments. The

procedure is to decide the plane of the scene on which the best focus is re"uired and

then set the lens focusing ring to the mid position. Then set the camera mechanical

adustment for ma&imum clarity. ?inal fine focusing can be carried out using the lens

ring.

The mechanical focusing on cameras is often called the bac focus! originally because

a screw at the bac of the camera moved the tube on a rac mechanism. odern

cameras now have many forms of mechanical adustment. Some have screws on the

side or the top! some still at the bac. There are cameras that have a combined C,CS-

mount on the front that also has the mechanical adustment and can accept either type

of lens format. The longer the focal length of the lens the more critical is the focusing.

This is a function of depth of field described later in this chapter.

Variable *ocal $ength

This is a design of lens that has a limited range of manual focal length adustment. 't

is strictly not a /oom lens because it has "uite a short focal length. They are usually

used in internal situations where a more precise adustment of the scene in view is

re"uired which may fall between two standard lenses. They are also useful where for a

small e&tra cost one lens may be specified for all the cameras in a system. This saves

much installation time and the cost of return visits to change lenses if the views are

not "uite right. ?or companies involved in many small to medium si/ed internal

installations such as retail shops and offices this can save on stoc holding. 't maes

the standardisation of systems and costing much easier.

Man!al +oom $ens

A /oom lens is one in which the focal length can be varied manually over a range.

5sually this is by means of a nurled ring on the lens body. 't has the connotation of

D/ooming inE and therefore infers a lens with a longer than normal focal length. (Say

31 | P a g e



more than ;@mm.) The /oom ratio is stated as being for instance >08! which means

that the longest focal length is si& times that of the shortest. The usual way of

describing a /oom lens is by the format si/e! /oom ratio and the shortest and longest

focal lengths. ?or e&ample! ;,<H! >08! 8;.@mm to @mm. Again! great care must be

taen in establishing both the camera and the lens format. The lens ust described

would have those focal lengths on a ;,<H camera but an e"uivalent range of Bmm to

=Bmm on a 8,;H camera.

Motorised +oom $ens

anual /oom lenses are not widely used in CCTV systems because the angle of tilt of

the camera often needs to be changed as the lens is /oomed in and out. The mostcommon need for a /oom lens is where used with a pan tilt unit. The lens /oom ring is

driven by tiny 7C motors and operated from a remote controller.

%ith the development of ever-smaller cameras and longer focal length lenses the

method of mounting the camera,lens combination must be considered. There are

many cases where the lens is considerably larger than the camera and it may be

necessary to mount the lens rigidly with the camera supported by it. 'n other cases! it

may be necessary to provide rigid supports for both camera and the lens. Always

chec the relationship between the camera and lens si/es and weights when selecting

a housing or mounting. ost manufacturers of housings can provide lens supports as

an accessory.

*oc!ssing a +oom $ens.

The most fre"uent reason for the focus changing when /ooming is that the mechanical

focus of the camera has not been set correctly. The following is the procedure for

setting up the focus on a camera fitted with a /oom lens.

The focusing ring should be mared DnearE and DfarE. Set this to DfarE and set the /oom

ring to the widest angle of view. Aim the camera at an obect about =F metres away

and adust the camera focus for ma&imum clarity. :e&t /oom in to an obect nearby

and set the lens focus for ma&imum clarity. 't should now be possible to /oom all the

32 | P a g e



way bac without the focus changing. any motorised /oom lenses will be used in

e&ternal conditions with limited light. 'f this is the case then it is advisable to fit a

neutral density filter in front of the lens to mae the iris open fully. A neutral density

filter is one that reduces the amount of light that enters the lens! evenly over the whole

of the visible spectrum. This will create the shortest depth of field and ensure setting

up more accurately for the worst conditions. The depth of field! as e&plained later!

depends on the aperture opening.

Some controllers can override the automatic iris mechanism! usually to open it to see

into darer areas. This is often the case when a camera is looing out over open

country in bright sunlight and the lens closes because it measures the average light

levels. The scene at ground level can be very dar in these conditions! with little

detail. This is not a desirable feature to include unless absolutely necessary. This is

because the override can be forgotten with resultant poor pictures being recorded if

the system is not fully monitored. The better solution is to tilt the camera down until

there is less proportion of sy in the picture.

Motorised +oom $enses with pre,sets

There are many situations where it is re"uired to pan! tilt! and /oom to a

predetermined position within the area being covered. 't is possible to obtain

motorised lenses with potentiometers fitted to the /oom and focusing mechanisms.

These cause the lens to /oom automatically and focus to the setting by measuring the

voltage across the potentiometer and comparing it with the signals in the control

system. All other functions are as for motorised /oom lenses. $re-set controls are only possible with telemetry controlled systems. The specification of the telemetry controls

should be checed to see whether the pre-set positions are set from the central

controller or locally from the telemetry receiver.

33 | P a g e



ris Control of $ens

Man!al ris

%ith this type of lens! the iris opening is set manually by rotating a nurled ring on

the lens body. Typically! it will have a range of settings from the ma&imum to fully

closed! although the adustment will be rather coarse. This type of lens is only suitable

for indoor applications where the light levels remain fairly constant. 't can also be

used indoors with cameras having electronic shutters maing a significant cost saving.

Care must be e&ercised in using this camera,lens combination in e&ternal applications

because the camera may not have ade"uate control to cover the total light range. 'n

addition! manual iris lenses do not usually have a neutral density spot filter to cope

with e&tremely bright sunlight.

'n many indoor situations! the general level of light will vary significantly between

summer and winter due to light from windows! sylights! etc. Therefore! it is often

necessary to adust the aperture two or three times a year to maintain optimum clarity

of the picture.

A!tomatic ris

7ue to ongoing development! tubed cameras were becoming more sensitive and their

use was spreading to more outdoor applications. They were very limited in the range

of light that could be coped with. To overcome this problem manual iris lenses were

fitted with motors bolted on to the barrel to drive the iris ring. The motors were

connected by way of an amplifier to the video output of the camera. This was

monitored to adust the iris ring according to the voltage of the video signal. The

lower the voltage then the more the iris would be opened until the correct video

voltage was achieved! and the reverse when the video voltage increased. The early

amplifiers suffered from the problem of being too sensitive and responding too

"uicly to changes in the video signal. This caused DhuntingE of the iris opening

control and resulted in fluctuating contrast of the picture. To overcome this a delay

circuit was introduced in the amplifier but this sometimes caused the reverse problem

of the picture changing too slowly.

34 | P a g e



odern automatic iris lenses are now completely self-contained units produced by the

lens manufacturer and containing very sophisticated electronics and microscopic

motors. There are three main types of automatic iris lenses.

ris Amplifier

This type of lens is sometimes referred to as a servo lens. The most common type

contains an amplifier and is connected to the video signal of the camera. 't is driven

by a dc voltage also provided from the camera. 't was mentioned in Chapter <! that the

voltage of the video signal is proportional to the amount of light on the imaging

device. The video level falls in proportion to the light level. The amplifier is

continuously monitoring this voltage to maintain it at 8-volt pea to pea. As the

voltage changes so the iris amplifier opens or closes the iris to maintain a constant 8-

volt.

ost cameras that provide an automatic iris drive include a socet on the rear. There

are three connections! Mv! Fv! video. 5nfortunately! there is no current standard for

this connector but most cameras are paced with the appropriate plug. This can create

problems if one camera is substituted for another mae during maintenance or service.

't can mean that the service engineer has to change the iris plug on site! which is not

an easy ob. 'n recognition of this problem! many cameras are now being produced

with screw terminals on the rear.

-alvanometric $ens

These are also nown as a galvometric or galvano lens. This type of automatic iris

lens is driven by a reference voltage produced by an amplifier in the camera. 'n other

words! the amplifier is within the camera instead of being part of the lens. The lens

contains a driving motor to open and close the lens and a damping coil to prevent

hunting. These lenses have four connections! Mve drive! -ve drive! Mve damping! and

-ve damping. The camera specification should be checed to ensure that it contains

the circuitry for this type of lens. Jalvanometric lenses are usually less e&pensive than

35 | P a g e



lenses with a built-in amplifier. They are simpler to install but can only be used with a

limited range of cameras. Again! for this type of lens many cameras are being

produced with screw connectors instead of a socet for the lens connection.

Sensor $ens

This lens includes a light sensor similar to that in a photographic camera. This

measures the light levels and adusts the iris aperture accordingly. 't re"uires a 8;-volt

dc supply that may be obtained from any source. This type of lens is not very

common now having been introduced for use on Vidicon cameras that did not have a

video and 8; volt output. The problem was that the light sensor was pre-set and not

responsive to the video level! therefore the correct level was always maintained. The

vast maority of cameras now provide an automatic lens connection therefore there

will only be rare cases where this lens will be re"uired.

$ens Parameters

*ocal $ength

The rays from infinitely distant obects are condensed by the lens at a common point

on the optical a&is. The point where the image sensor of the camera is to be placed is

called the focal point. A lens has two focal points! the primary principal point and the

secondary principal point. The distance between the secondary principal point and the

plane of the image sensor is the focal length of the lens.

36 | P a g e



7iagram =. < ?ocal 9ength of 9enses

Angle of View of $enses

This is the angle that the two lines from the secondary principal point mae with the

edges of the image sensor. The focal length of a lens is fi&ed whatever the si/e of the

image sensor. The angle of view however varies according the si/e of the sensor.

7iagram =. = Angle of View

The angle of view is given by the following formula0

The angle of view for a given focal length lens varies according to the sensor si/e.

This is shown in diagram =.@. The corollary of this is that for a given view the

re"uired focal length varies according to the sensor si/e as shown in diagram =.>. This

37 | P a g e



illustrates that for the same field of view! the smaller the format the shorter is the

re"uired focal length.

7iagram =. @ Angles of View for 7ifferent Sensor Si/es

7iagram =. > ?ocal 9engths for 7ifferent Sensor Si/es

*ield Of View

The field of view is the ratio of the sensor si/e to the focal length and the distance to

the subect. This is shown in diagram =.. The Dwidth to heightE ratio of the sensor is

=0<. The hori/ontal and vertical angles and therefore fields of view are different and

must be considered separately.

38 | P a g e



7iagram =. ?ield f View

Sensor Sies

7iagram =.B shows the sensor si/es to be used when calculating fields of view and

angles of view.

7iagram =. B Sensor 7imensions

?or e&ample! if it were re"uired to view a subect ;.@ high at a distance of 8F

using a ;,<H camera and lens the calculation would be as below. 5sing the

relationships given in diagram =.>.

The nearest standard lens in this case would be a ;@mm and the actual height of the

subect scene would be ;.>= . The slightly shorter focal length lens provides a

slightly wider angle of view.

ost lens brochures give the hori/ontal and vertical angles of view. The relevant

views can be calculated from the formula as follows0

39 | P a g e



%here0 H is the height of the scene! d is the distance from the camera to the scene.

This would give the vertical height of the scene using the vertical angle of view.

Similarly! the hori/ontal width of the scene would be calculated from the hori/ontal

angle of view.

Relationship %etween Sensor Sie and $ens Sie

't can be very confusing to establish the actual field of view that will be obtained from

a combination of sensor si/e and lens specification. 9enses are specified as designed

for a particular sensor si/e. A lens designed for one sensor si/e may be used on a

smaller si/e but not the reverse. The reason is that the e&tremities of the scene will be

outside the area of the sensor. any people in the CCTV industry have grown up with

the ;,<H camera as the most popular and are familiar with the fields of view produced.

1owever the 8,;H and 8,<H cameras are now being e&tensively used and therefore

there are important factors that must be taen account.

7iagram =. 4ffect of Sensor Si/e on View

7iagram =. shows the effect of using one lens on two different si/es of sensor. The

result of using a larger lens format on a smaller lens format is to create the effect of a

longer focal length! which is a narrower angle of view.

40 | P a g e



7iagram =. 8F 5sing a Correctly atched Camera and 9ens ?ormat

7iagram =.8F shows the result of using a lens designed for a 8,;H format on a 8,;H

sensor. This is an important consideration when deciding the most appropriate lens for a re"uired field of view. The design si/e of the lens must be related to the si/e of the

sensor being used. To summarise then0

8. A lens designed for one format may be used on a smaller format camera but

will produce a narrower angle of view.

;. A lens designed for one format may not be used on a larger format camera.

<. Assuming a focal length has been assessed based on a particular format of

camera and lens! and it is then decided to use a smaller format camera! the

same field of view will only be obtained if a shorter focal length lens is used.

=. Always chec the angle of view for the particular lens and camera

combination it is intended to use.

@. Charts at the end of this chapter provide guidance on the selection of lenses

and the relationship between different formats of camera and lenses.

Apert!re

The si/e of the aperture is called the Df numberE of the lens! e.g. f8.=! f8.;! etc. This is

a mechanical ratio of the lens components and is specified as0

41 | P a g e



The effective diameter is related to the si/e of the front lens. :ote that this is effective

diameter and not the actual diameter. This is a measure of the amount of light that the

lens will pass to the imaging device. As stated it is a ratio and does not refer to the

"uality of the lens. The smaller the number then the larger is the aperture. The figure

given in specifications for lenses is the ma&imum aperture and this value is often

followed by the minimum aperture. ?or instance! f8.= -- f<>F! this second value being

important if the camera is very sensitive such as an intensified sensor. 'ntensified

cameras often re"uire a minimum aperture as small as f8@FF. ?rom the formula above

it may be calculated that with a 8>mm lens having the aperture set to f<>F the

effective diameter will be only F.F=mm. 4ven so! this could allow too much light to

the sensor of an intensified camera and damage the tube or flare out the picture.

1aving said that the f-number is a ratio! this does not imply that a lens with a lower

number is better than one with a higher number. There are other factors that affect the

light transmission through a lens. 1owever! when comparing the maor brands of

lenses it is sufficient to use the f-number unless the application is especially

demanding! where! for instance! image comparison or ultra fine resolution is

necessary.

The efficiency of a lens and the amount of light it can transmit depend on many

factors that lens designers must consider. 1owever! ultimately a lens must be a

commercial proposition and affordable to the CCTV installer and the customer. Two

factors that affect the cost of a lens are the si/e of the glass elements and the number

of elements. Therefore! it is less e&pensive to produce a 8>mm f8.B lens than it is to

produce a 8>mm f8.;. Conse"uently! some manufacturers produce the same focal

length lens in two variations of f-number. ?or indoor conditions with ample light! or

outdoor use in daylight only! the cheaper f 8.B lens would be satisfactory and could

represent a saving in cost. 4&ercise care in selecting the cheaper lens if the application

is outdoors with low light conditions. As can be seen from this chapter! this would

re"uire nearly three times as much light as the f8.; lens.

42 | P a g e



2 -ONITOR&

ntrod!ction

Another important and often overlooed part of a CCTV system is the monitor.

5ltimately the picture taen by the camera and the lens is displayed on the monitor.

The monitorEs performance and adustment will have an affect on the picture seen by

the system operator.

'n the same way that cameras! being analogue devices! have adustments that enable

the best picture "uality to be obtained so monitors! also being analogue devices! have

settings and adustments that enable the best picture to be displayed. 'f the controls on

the monitor are not correctly set then! similarly! the money spent on e&pensive high

performance cameras! lenses and control e"uipment will be a waste because the

picture displayed on the monitor will not do ustice to the rest of the system.

Conse"uently! it is vital to understand the principles of the normal monitor controls!

their effect on picture "uality and the correct way to set the controls properly.

onitors are available in different screen si/es. The reason for this is that the si/e of

the monitor depends on the viewing distance. 'f the incorrect si/e or position of a

monitor is used then at best the monitor will be awward and unpleasant to use at

worst the picture will be too small to differentiate detail or so large that the picture

appears grainy and low "uality.

43 | P a g e



'n this chapter the principles of operation of monochrome and colour monitors will be

e&plained in a simplified way! leading to the principles and effects of their controls.

The correct procedures used to set the controls to obtain the best picture "uality will

be described. ?inally! the principles of choosing the correct number! si/e and

positioning of monitors will be discussed so as to get the ma&imum from this

normally undervalued part of CCTV systems.

The Principles of Monochrome Monitor Operation

Apart from the use of transistors! integrated circuits and other solid state devices in

the circuits of monitors the maor part of the monitor! the television or Cathode 2ay

Tube (C2T)! has remained essentially unchanged since the first TV monitors were

developed.

As shown in 7iagram @.8 the C2T consists of a glass tube with all the air removed.

An electron gun at the bac of the C2T (a special material that when heated Gboils

offH electrons) generates a stream of electrons. These are attracted to the front screen

at very high speed by a high voltage of several thousand volts. The inside of the

screen is coated with a special phosphor that glows when struc by the electron

beam! the stronger the beam the brighter the spot generated.

Scanning coils around the nec of the tube generate a magnetic field. The magnetic

field affects the position of the striing point of the beam on the screen. #y changing

the voltage on the scanning coils the striing point of the beam can be scanned across

the screen of the C2T to create a series of lines when the beam moves bac across the

screen! during the retrace! the beam is turned off so that only the line and not the

retrace is visible. #y selecting the correct wave shape and fre"uency the same >;@

line frame and @F fields per second patterns as produced by the camera can be re-

created ?or descriptions of fields! frames and the way that the camera produces these

see ChaptersE two and three

44 | P a g e



Diagram 32 1 T!e Cat!)de Ra' T(#e

The video signal is used to control the strength of the beam. The brightness of the

beam at any point along a given line will be proportional to the level of the video

signal. This is conse"uently proportional to the light intensity at that point on the

image sensor of the camera. 'n this way the picture captured by the camera can be

recreated on the screen of the monitor and observed by the system operator.

Diagram 32 4 Basic -)n)c!r)me -)nit)r Bl)c$ Diagram

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'n a basic monitor the video signal input enters the monitor and is terminated in a

seventy-five ohm load. This matches the output impedance of the camera and the

coa&ial cable (see Chapter three). A sync separator separates the video signal and sync

pulses. The sync pulses are used to synchronise the line oscillator of the monitor to

the line oscillator of the camera being viewed. The line oscillator and field oscillator

respectively control the scanning coils that scan the electron beam into >;@ lines.

?ield sync pulses control the scanning coils to produce @F fields. The hori/ontal and

vertical hold controls adust the fre"uency of the line oscillator. Conse"uently! these

can be used to compensate for differences in the sync pulse fre"uencies coming from

the camera.

A high voltage generator is used to accelerate the electron beam. The strength of the

beam is controlled by the output of an amplifier. The input of the amplifier is the

video signal. 'n this way! the level of the video signal controls the brightness at any

point on the screen. The brightness control sets the basic level of the beam and

therefore the general brightness of the picture. The contrast control controls the

amplification or gain of the amplifier. The greater the contrast the greater is the effect

of the video signal on the brightness. At low contrast! the picture will appear grey and

uninteresting. At e&cessive contrast! the blacs and whites in the picture are very

harsh and the picture is unpleasant to view. At the correct brightness and contrast

levels! the picture will appear natural with many shades of grey. The 7C 2estoration

affects the overall voltage level of the video signal. Sometimes this is needed because

the voltage is modified as it passes through capacitors in the circuits of cameras and

control e"uipment. %ith the 7C restoration turned off there will be a grey GrasterH

when no video is input to the monitor. %ith the 7C restoration turned on the screen

will be completely blac when no video is input.

Principles of Colo!r Monitor Operation

A colour monitor wors in basically the same way as a monochrome monitor e&cept

that there are three electron guns. These three guns are for the three primary colours!

red! green! and blue. The guns are aligned to the mas on the phosphor screen. 'f a TVscreen is e&amined closely! it can be seen that it is a matri& of very fine red! green and

46 | P a g e



blue dots. This is why the resolution of colour monitors is typically lower than

monochrome monitors.

A combination of all three dots is needed to generate white compared with a single

dot for a monochrome monitor. This means that for the same number of pi&els the

ability to resolve blac and white lines may be up to three times less on a colour

monitor. %hen the beam from the correct gun stries a spot or pi&el on the

corresponding mas then the pi&el glows red! green! or blue. As previously e&plained

in Chapter two! combinations of these three basic colours can be used to form any

colour in the spectrum. The firing of the guns in combination by the colour composite

video signal recreates the colour picture viewed by the camera.

Diagram 32 5 C)l)(r -)nit)r Bl)c$ Diagram

After sync separation the combined chrominance and luminance signals are processed

by decoder and amplifier circuits. These are divided into separate signals to control

the strength of the red! blue and green electron guns. #esides the normal brightness

and contrast controls there is also a colour control that affects the general

chrominance of the picture. %ith the control wound to minimum! the image will be

monochrome. %hen the control is turned to ma&imum the colours will be very

saturated and will normally be too unpleasant to view.

5sually a composite colour video input is provided but on some monitors a I-C or

Super V1S input will be provided. Alternatively! an input is provided where all three

47 | P a g e



colour signals are brought in separately. This is nown as an 2J# (red! green! blue)

input. The advantage of either I-C or 2J# inputs is that there is no filtering as

associated with colour composite video. The bandwidth available is higher! and

conse"uently higher resolution is available if the I-C or 2J# inputs are used. That is!

provided of course that I-C or 2J# has been used throughout the system.

/nderstanding monitor performance specifications

Resol!tion

As with cameras! the vertical resolution of a monitor is the number of blac to white

transitions or lines that can be distinguished from the top to the bottom of the picture.

'n addition! as with cameras the limiting factor is the @@ lines that mae up the

picture. The figure for resolution that is normally given in monitor data sheets is! as

for cameras! the hori/ontal resolution. That is to say! the number of blac to white

transitions or lines that can be resolved along one hori/ontal line of the picture.

The maor difference between resolution performance figures for monitors and

resolution for CC7 cameras is that the figure for monitors is given for the centre of

the picture. This is where the resolution is highest.

Diagram 32 T!e Effect Of &canning C)ils On Res)l(ti)n And 6inearit'

The reason for this is that the picture is made by >;@ hori/ontal lines produced by the

scanning coils using a magnetic field to drive the beam of electrons across the

phosphor screen. 1owever! it is very difficult to get a magnetic field to have an even

or linear effect across the entire surface of the screen. At the edges of the screen! the

48 | P a g e



magnetic field tends to be non-linear and both the hori/ontal and vertical lines seen on

the screen will appear bent. The electron beam also tends to defocus towards the

edges. This reduces the ability to distinguish fine lines at the corners and sides of the

screen and reduces resolution at these areas. ?or e&ample! a monitor with a resolution

at the centre of >FF lines might only have a resolution of =FF lines at the corners. This

is a very important point to remember in choosing a monitor and in positioning a

camera on the screen to see the most detail. The obect to be viewed must be placed in

the centre of the screen to get the sharpest picture.

The problems of non-linearity became worse with the advent of flatter and s"uarer

tubes! because the scanning beam! which is linear had to travel further to the edges of

the screen than it did to the centre. This problem was is overcome with a

compensation circuit called DSE correction. This causes the beam! now non-linear to

move slower towards the edge and faster in the centre.

onochrome monitor hori/ontal resolution is normally "uite high! between @F and

BFF lines for a nine-inch monitor. The reason is because the coating of phosphor on

the inside of the screen is continuous and the spot si/e is determined by the electron

beam focus. Conse"uently! in monochrome systems the monitor is not the limiting

factor for the resolution of the system. The resolution tends to decrease slightly as the

monitor si/e increases because it is more difficult to manufacture large TV tubes with

a fine phosphor coating.

'n colour monitors! however! because there are three spots to mae each point! red!

green and blue! the resolution is very much lower typically <<F to <@F lines. The

highest resolution that is being achieved at this time is about =@F lines. This is

assuming that the I-C input of the monitor is used. That! of course! has the proviso

that all the other parts of the system are I-C and have the same or higher resolution

figures.

#andwidth is also lined to resolution (see Chapter < and the section on camera

resolution) The greater the bandwidth the higher the possible resolution of the monitor

and the sharper the pictures will be. ?or a @F-line monitor the bandwidth might

typically be about 8F1/.

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http://www.cctv-information.co.uk/i/Cameras

http://www.cctv-information.co.uk/i/Cameras



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5. VIDEO S!ITC"IN#

ntrod!ction

There are few CCTV systems that have only a single camera apart from door entry or

vehicle rear view systems! etc. ost systems incorporate more than one camera and

therefore have the need to select the view from any camera on to a monitor. This

chapter covers the main types of video switcher and their applications.

$rinciples of Video Switching

't would be possible to switch video signals using simple toggle switches but this

would introduce several undesirable results. The switching could cause severe

interference on the screen due to the induced noise on to the signal. There would be a

lot of picture roll until the monitor became synchronised to the ne&t camera. The

picture might be unstable until the monitor is synchronised correctly.

odern video switchers incorporate electronic switches and a techni"ue nown as

Dvertical intervalE switching. %hen a new camera is selected! the electronic circuits

wait a fraction of a second until the field sync pulse of the video signal is detected and

then switch over. This allows the monitor to loc immediately on to the new line sync

pulse and the new picture is displayed without any rolling. This assumes that all the

cameras in the system are compatible and on the same phase of the supply. The

elimination of picture bounce is the main reason for specifying that all cameras are on

the same phase of the supply. There are cases where it is not possible to connect all

51 | P a g e



cameras to the same phase such as large industrial sites or systems having cameras in

several buildings. There are cameras available with Dphase adustmentE controls. This

allows the video signal to be transmitted out of phase from the local supply and in

phase with the other cameras. 'n many cases! the adustment is too coarse for accurate

alignment and the result would be a small amount of DbounceE but not a complete roll

of the picture. The measurement should be carried out at the monitor using a dual

trace oscilloscope. ne trace would show the local mains sine wave. The other would

show the camera output and its relationship to the supply.

The %asic Video Switcher

The simplest switcher is one that includes the features mentioned previously and

where the coa&ial cables are connected directly into the rear via #:C plugs. These

switchers usually have a number of buttons according to the number of cameras in the

system. They are mainly ;! =! >! and B way units. This type of switcher is usually

nown as a manual switcher where the eys directly switch the cameras.

Switchers are usually terminated with a @-ohm resistor! as is the monitor. 'n the case

of the system shown in diagram >.8 the terminations at both the switcher and the

monitor should be left at @ ohms.

ost switchers have two other controls! one to set the cameras to se"uence

automatically! the other to adust the dwell time between switching from one camera

to the ne&t. The dwell time will be the same for each camera in the system.

52 | P a g e



Diagram 721 &'stem it! &im+le -an(al &itc!er

$ooping Switchers

n occasions! it may be re"uired to loop one or more cameras to part of the system or

another switcher! for dual control. 1ere a switcher with loop through facility would be

used. This type of switcher will have two rows of #:C connectors! one above the

other. There will also be a switch adacent to each camera input! the purpose of which

is to set the @-ohm termination on or off. ne position of the switch will usually be

mared Dhigh!E the other DlowE or @ ohm. The camera inputs are normally the top row

of connectors with a corresponding loop through connector below. The camera signals

that are re"uired to carry on to another location would be taen off the output

connectors via #:C plugs. The termination switch ne&t to each looped through

camera should be set to Dhigh.E The signal should then be terminated at @ ohms at its

53 | P a g e



destination. Some switchers with looping outputs do not have a termination switch.

'nstead the resistance is set to DhighE and plugs with a built-in @-ohm resistor are

provided to fit in unused outputs.

't is not acceptable to loop through a video signal by using a #:C DteeE connector. 'f

this is the only way available then the internal @-ohm resistor inside the unit should

be snipped out! The correct termination at the end of the line should be ensured.

Diagram 724 Rear Panel )f 6))+ing &itc!er2

Switchers with Additional *eat!res

Switchers are available with two monitor outputs. :ormally one monitor can be set to

se"uence through the cameras and the other used as a selectable spot monitor.

Another feature available on many switchers is the capability to accept alarm inputs.

There is usually one alarm input to each camera input. 'f there is an input from an

alarm! the switcher will automatically switch the monitor to the associated camera. An

alarm input will override a se"uence if it is set up and hold the selected camera on the

monitor. 'n the case of a switcher with dual monitor outputs one monitor will switch

to the alarmed camera while the other continues to se"uence.

Remote Switchers

ften it may be inconvenient or difficult to route all the coa&ial cables to a destop

switcher. This is especially the case if there are eight! si&teen or more cameras in the

system. A remote switcher is one where the camera cables are connected into a panel

containing all the switching electronics. This bo& can be situated anywhere

54 | P a g e



convenient for routing the cables. The destop control unit is then connected to the

remote panel by a small two or four core cable or sometimes a single coa&ial cable.

The coa&ial cable to the monitor(s) is connected to the remote panel.

Diagram 725 &'stem it! Rem)te &itc!er2

2emote switchers can generally be more sophisticated than the destop type and can

incorporate more features. There can be up to si& or eight monitor outputs and more

versatile handling of alarm inputs. 'n addition! several eyboards may be incorporated

into one system. This allows selection of cameras from more than one control

position. The controls in this type of system are generally of the master and slave

type! which means that the controls are not totally independent. %here greater

fle&ibility is re"uired then the choice would be to use a matri& switcher as described

in the following section.

?or a system with more than four cameras! remote switchers can achieve significant

savings in installation costs.

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72 ANA6OGUE %IDEO RECORDING

The human eye is an incredibly adaptable device that can focus on distant obects and

immediately refocus on something close by. 't can loo into the distance or at a wide

angle nearby. 't can see in bright light or at dus! adusting automatically as it does so.'t also has a long *depth of field* therefore! scenes over a long distance can be in focus

simultaneously. 't sees colour when there is sufficient light! but switches to

monochrome vision when there is not. 't is also connected to a brain that has a faster

updating and retentive memory than any computer. Therefore! the eyes can swivel

from side to side and up and down! retaining a clear picture of what was scanned. The

brain accepts all the data and maes an immediate decision to move to a particular

image of interest! select the appropriate angle of view and refocus. The eye has

another clever tric in that it can view a scene of great contrast and adust only to the

part of it that is of interest.

ntrod!ction

The predominant method of recording video pictures at the time of publication of this

boo is by analogue video recording. 'n analogue recording! the voltages that mae

the composite video signal are recorded on to magnetic tape the changes in voltage

magnetise and demagnetise the tape. To play bac the recording the changes in

magnetism on the tape are converted bac in to voltages and the composite video

signal is re-created for connection to a video monitor.

A video tape recorder is a comple& integration of electronics and e&tremely high

precision mechanics. There have been several types of recording systems in recent

56 | P a g e



years! the main contenders being *#etama&* from Sony! *Video ;FFF* from $hilips and

*V1S* from atsushita. They are all based around a tape contained in a cassette with a

supply spool and a tae up spool. 1owever! there were both electronic and mechanical

differences that prevented one tape being used on another mae. The one to emerge as

the standard throughout the world is the V1S system. V1S means Video 1ome

System and was developed by the 3VC Company in 3apan.

The V0S Video Recorder

All video tape recorders follow the same principles as an audiocassette recorder. That

is! a tape containing thousands of tiny magnets! each with a north and a south pole is

passed through a varying magnetic field. The magnetic field is generated in a

revolving drum from the video signal. This reproduces the video signal onto the tape.

The tape is stored in a sealed cassette with a flap at the front protecting the tape.

%hen the tape is loaded into the recorder! a mechanism draws the cassette into and

down the machine.

The catch holding the front cover is released and the cover opened. The cassette drops

over two threading posts as shown in the first diagram. %hen one of the functions

such as play or record is operated the tape is drawn around the head drum as shown in

the second diagram.

7iagram . 8 V1S Tape Cassette.

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Principles of Video Recording

The descriptions give here are of necessity over simplified and are intended to

illustrate the basic principles of recording. As stated before! the two essential elements

of a video tape recorder are a rotating head assembly and the tape passing around a

drum and head. The head consists of a ferrite ring with its continuity broen by a

small gap. A coil is wound round the ring which! when energised! creates a magnetic

field. The magnetic field in the ring concentrates in the gap. An essential aspect of

design is that head gap is in the order of F.< microns. A micron is one-millionth of a

metre. Therefore! F.< microns is about one-hundredth the thicness of a human hair.

The video signal is fed to the magnetic coil and creates an analogue version in the

form of a magnetic field. As the tape passes the gap in the head the magnetic field

causes the *internal magnets* to align according to the signal passing through the head.

This maes a magnetic copy of the signal on the tape. The tape passes the drum at a

fi&ed speed! therefore low fre"uencies will create long *magnets* in the tape! and high

fre"uencies will create short *magnets*.

Trac1s on Tape

The tape consists of an insulated base material with a fine o&ide coating. ?or various

reasons! the head is displaced at an angle to the tape. This is nown as helical

scanning and is standard for all recorders. The magnetic information is recorded at an

angle across the tape.

7iagram . ; Tracs on Video Tape

The width of tape for standard V1S is 8;.>@mm (8,;+). The speed for standard real

time recording is ;<.< mm,sec. 4arly video recorders and some domestic V1S

58 | P a g e



recorders still available today had two coils! or heads! on each head cylinder. This

wored well while the tape was moving! producing moving pictures on playbac.

1owever! when the pause function on the recorder was activated to view a single still

picture hori/ontal noise bars would appear on the picture because the head was not

moving fast enough to capture the single picture from the tape accurately.

The solution to this problem was introduced when the first four-head video recorders

were made. These use four coils or heads! two each on opposite sides of the head

cylinder. #y using four heads instead of two twice the amount of information could be

written to or read from the tape. ?our head video recorders can replay still imageswithout any noise bars and this has led to their general use in domestic and CCTV

video recorders! replacing the older two-head design.

The heads are spaced >@ microns apart for a standard V1S time-lapse recorder and

these lay down tracs on to the tape! which are @B microns wide. 1ead cylinders of

this design are nown as type S$ heads.

82 DIGITA6 TECHNO6OG9 AND RECORDING

ntrod!ction

Recent developments have made it possible to store video images on magnetic discs,

as on a computer hard disc. This is done by converting the image to a digital form to

store it. The early problem was that to obtain reasonable resolution required storing a

massive amount of data. The result is that only a limited number of images could be

stored. A reasonable quality colour picture with a resolution of 681 !8" piels has

#$6,%%% picture elements. This would need about 1&# megabyte '(b) of disc storage.

59 | P a g e



odern digital compression technology now means that many more images can be

stored. There are now systems that can store thousands of images. 4ven this must be

considered in the light of the "uality of image and the amount that can be stored. ?or

instance! real time video is presented at the rate of ;@ frames per second! i.e. F!FFF

frames per hour. A 8FF-b hard disc would store <<F frames! which is only 8<

seconds of video at normal density. A compression of ;08 still only stores about ;>

seconds of live video. Sampling every other frame would double this again but it can

be seen that digital storage has a long way to go before replacing the video recorder.

1aving said this! technology in this field is advancing at a very fast rate and is the

obvious way forward.

7igital recorders are available but their use is a tiny fraction of that of analogue video

recorders. This is no surprise as a videotape costing a few pounds can store over

=<;!FFF high "uality colour images! using a recorder costing a few hundred pounds.

To store the same number of pictures digitally is very costly both in storage media and

hardware re"uired to write to it.

The primary successes of digital recorders have been in event recording! where fast

recording and search maes digital recorders most attractive. any digital recorders

include multiple&ers as the timebase corrector re"uired for digitising means that

comparatively little e&tra circuitry is needed to add this feature! which helps to mae

them cost effective.

This was the original introduction to digital recording in the second edition published

in ;FFF and would have been written in about 8. Technology has moved on at a

fast pace since then. 'n fact it is now at the stage where digital recording is virtually

the norm with the use of analogue VC2s declining rapidly.

Along side this massive development is the growth of '$ technology! which now has

the following complete chapter () devoted to this latest trend.

60 | P a g e



The &igital Video Recorder '&VR(

The essential elements of any digital video recorder are shown in the simplified bloc

diagram B.8. any 7V2s have more components to add additional features lie

motion detection or video transmission. The switcher selects which camera is to be

recorded at any moment and routes it to a timebase corrector. The timebase corrector

ensures that pictures can be recorded rapidly in se"uence without having to

synchronise the cameras by gen loc or other means.

The analogue to digital converter (A7C) turns the voltages representing luminance

and into an array of binary digital numbers which represent the brightness and colour

at every point on the video picture. A digital signal processor taes this huge amount

of raw data and compresses it so that an acceptable number of pictures can be stored

on the limited space available in the digital store. The store taes this information and

holds it! usually under a reference related to the time and date of recording.

Diagram :2 1 &im+lified Bl)c$ Diagram Digital %ide) Rec)rder

At any time this archived information can be retrieved and routed via a digital to

analogue converter to re-create the video signal re"uired to play bac the recording on

a conventional video monitor. Alternatively! if a $ersonal Computer is being used as a

61 | P a g e



digital recorder the playbac pictures may stay in digital form for display on the $C

monitor.

/nits of meas!re for digital storage

Storage and file si/es are measured in bytes where one byte is the basic unit of storage

that would represent a single letter or number. A byte comprises eight bits. ne bit is a

single binary number either 8 or F.

ne Nilobyte O 8!F;= bytes! (;8F ) not 8!FFF as is commonly used.

ne egabyte O 8!F;= Nilobytes O 8!F=B!@> bytes (;;F).

ne Jigabyte O 8!F;= egabytes O 8!F=B!@> Nilobytes O 8!F<!=8!B;= bytes (;<F)

n Terabyte O 8!F;= Jigabytes! (;=F bytes).

The above relationships between units are strictly correct! however it is common

practice to use a factor of 8!FFF as the ratio between units.

Principles of &igital Video Recording

'n digital recording each field is divided in to an array of individual points or pi&els.

At each one of these points! analogue to digital converters convert voltages

representing the colour and brightness at that point to a binary digital number. This

array of binary digital numbers can then be stored digitally in a file with a name cross

referenced against time and date. A single frame of monochrome video needs about

=@Fb (Nilobytes) of space for storage and single frame of colour needs about >@Fb.

This is the uncompressed si/e that would be needed for storage on hard disc or other

storage medium.

Conse"uently to store the same number of images as a video tape a total storage

capacity of about 8;8.@Jb (Jigabytes) would be needed for monochrome and

62 | P a g e



8@.@Jb for colour. This is considerably larger than hard discs and other media

generally available and would also be very e&pensive. Conse"uently some means is

re"uired of reducing the amount of space re"uired without adversely affecting picture

"uality. The techni"ue of reducing the amount of space re"uired is generally referred

to as compression.

The video frame contains a large amount of redundant information that can be

eliminated without a great loss in perceived picture "uality. Conse"uently! common

types of compression used are nown as Glossy compressionH because the redundant

information is discarded. ost compression methods are effective up to a certain

point! or GNneeH! beyond which the image "uality "uicly degrades.

To assist in reducing the amount of si/e re"uired for storage the video signal can be

represented in a form nown as I5V. The I5V format consists of the I (luminance)

and 5V (colour difference) signals (for further descriptions of luminance and video

signal components see chapter ;). The advantage of using I5V format is that fewer

bytes are needed to digitise the video. :ormally! recording all of the colour

components red! green! blue (2J# recording) would need three bytes! one byte for

each colour. #y using I5V format the luminance can be digitised as one byte and the

colour difference signal as one byte. Conse"uently only two bytes are needed rather

than three! a saving of one third of the storage space re"uired. This techni"ue can be

used together with compression to minimise the amount of space re"uired for storage.

Types of Compression

The technology for compressing video pictures originated in the storage of still

photographs on computers. The most commonly used standard! 3$4J! taes itEs name

from the 3oint $hotographic 4&pert Jroup by whom it was developed. 5sing 3$4J

compression! the nee occurs at about B08 compression. The most commonly used

standard is otion 3$4J for which the nee occurs at about 8@08 compression.

Conse"uently! -3$4J reduces a =@Fb file to only <Fb. %hile this is still too large

to fit the same number of images as a video tape on to a hard dis it is small enough to

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permit! say! ; images per second to be recorded for ;= hours on to a >Jb hard dis!

which is a si/e generally available! costing a few hundred pounds.

Another more recent compression standard was devised by the otion $icture 4&pert

Jroup specifically for the digitisation of moving images. This standard is given the

name $4J. This standard maes use of the redundancy between adacent frames.

-PEG.1 contains three types of encoded frames. 'ntracoded frames ('-frames)

contain all of the video information re"uired to mae a complete picture. $redicted

frames ($-frames) are generated by previous '-frames or $-frames and are used to

generate future $-frames. #i-directional $redicted frames (#-frames) are generated

using both previous and future frames. A complete se"uence of frames is made up of aseries of these different frame types with more than one '-frame for every 8F $- or #-

frames. This process is nown as inter-frame correlation and allows compression

ratios of 8FF08 to be achieved.

-PEG.4 is the format used in the latest 7igital Video7is (7V7) technology! which

can store about F minutes of V1S "uality video and audio on to only >@Fb of

storage space! such as a C7-2. 1owever there are a number of disadvantages to

$4J compression. ?irstly! in order for $4J to achieve high compression it needs

the video signal not to change abruptly from frame to frame. Since many video

recording applications re"uire multiple&ing because more than one camera must be

recorded! the rapid change from frame to frame as cameras are switched defeats the

inter-frame correlation techni"ue used in $4J. Secondly! $4J re"uires much

more electronics than 3$4J maing it more more e&pensive for security applications.

-PEG. is the latest development in the $4J series and is mainly used in videofilms. :ote! there was no $4J-<.

;OR-AT KNEE <ITH INTER.;RA-E CORRE6ATION

3$4J = - B 0 8 :ot Available

-3$4J 8F - 8@ 0 8 :ot Available

$4J 8F - 8@ 0 8 8FF 0 8

?2ACTA9 ;F - <F 0 8 P 8FF 0 8

%AV494T <F 0 8 P 8FF 0 8

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There are two other methods of compression worthy of mention.

H247 standard based video compression core technology with substantially increased

coding efficiency and enhanced robustness to networ environments in cost effective

embedded platform. This technology will support TV broadcast! digital entertainment!

internet streaming and visual communications over broadband and wireless networs.

<A%E6ET=> is als) seen as )ffering s(+eri)r de"el)+ment +)tential t) c(rrent

-PEG c)m+ressi)n> gi"ing a greater am)(nt )f c)m+ressi)n it! e/(i"alent

/(alit'2 It transf)rms t!e !)le image and n)t 0(st #l)c$s )f t!e image> s) as t!e

c)m+ressi)n rates increase> t!e image degrades gracef(ll'> rat!er t!an int) t!e

?#l)c$'@ artefacts seen it! s)me )t!er c)m+ressi)n met!)ds2 <a"elet

a++licati)ns can !a"e t!eir +referred le"el )f c)m+ressi)n selected #' t!e (ser

!ig!er )r l)er2

Thus! although %avelet is not as established as some other compression techni"ues! it

is growing in popularity.

Compression s!mmary

Compression technology is development rapidly! which maes it very dificult to

assess the true benefits of any particular method used in security applications. 4ach

manufacturer! naturally! pushes their own preference but it still leaves a ungle for the

end user to find their way through.

?ractal compression is not found very often in CCTV applications but is mentioned

here for completeness. 't is a mathematical method of encoding that re"uires a great

deal of computing power to encode the images. 't is not a DlossyE compression as in

3$4J or $4J. ne advantage is that the image can be enlarged or reduced without

the DblocyE appearance of other forms of lossy compression.

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Storage Rate

Another factor involved in digital recording is that of storage rate. %oring at the full

;@ frames per second of real time video would not only re"uire vast amounts of

storage (=.@Jb for ust one hour Q <Fb per frame) but also very fast processing and

storage media capable of digitising and storing a each frame (even at <Fb) in under

F.F= seconds =F milliseconds.

any 7V2s currently available! particularly those based on hard disc storage get

round this problem by sampling and recording frames at lower than the full ;@ frame

per second rate. This is e&pressed in a number of ways. ?or e&ample! a 7V2 may

record every 8;th frame! ; frames per second or R a second per frame. All of these

are the same value.

The combination of file si/e and storage rate will give a figure for storage capacity

per second. ?or e&ample! to store a <Fb file at <.8< frames per second re"uires <F &

<.8< O <.b per second! or F.<=Jb per hour. 1owever! this is ust for one camera

and most systems have more than one camera that must be recorded. ?or B cameras

the figure above would need to be multiplied by B which is ;.;Jb. To record these B

cameras for B hours would need B times the storage space again! ;8.>Jb. There are

currently ;<Jb hard discs that would accommodate such storage.

Conditional Refreshment

A techni"ue is now being used by which the first frame of a scene is captured and

stored at the highest possible resolution. Subse"uent frames are scanned and only

those parts of the scene that have changed are stored! These refreshed scenes are

superimposed onto the original frame and the changed parts updated. The refreshed

scenes use only a tiny amount of data storage compared to the original scene. 'n this

way! the storage capacity can be increased by one hundred or one thousand times

according to the amount of movement in the scene.

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8. IP TEC"NOLO#$

ntrod!ction

't used to be that CCTV images were always transferred over coa&ial cable! for

various reasons0 range! bandwidth! ease of installation! low attenuation! and so on.

1owever! there is a trend which is emerging to integrate CCTV images into (or over)

e&isting digital networs which are there to provide data services. The reasons for this

trend would appear! on the face of it! to be unarguable0 most organisations have large

data networs already there is often spare capacity (although the networ manager

may disagree with that statement) twisted pair cable e&tends everywhere it is simple

to install and maintain it maes ma&imum use of (or DleveragesE) an e&pensive asset.

There are downsides to the integration of data and images on a single infrastructure!

usually to do with two things0 the effect on data patterns caused by streaming video!

and the problems of reliability and resilience in a networ where 8FFL uptime is

usually an impossibility.

This chapter acts as a simple guide to networing which hopefully will cover a lot of

what you wanted to now about networing. This is not an in-depth technical guide0

there are already too many of those around. 2ather! it loos at an overview of

networing from the data perspective! and then deals with the issues of adding CCTV

to the infrastructure.

The first part loos at what a networ is and how simple networs operate. This leads

on to chec out protocols! and in particular! the S' layer model. Then TC$,'$! '$

addresses and gateways are dealt with. 9ocal Area :etwors are looed at0 how they

wor! and what to loo out for when CCTV is added. 4thernet will be described! the

worldEs most popular 9A:! and the difference between hubs and switches will be

e&amined. 9ater! the 'nternet is described0 where it came from and how it wors what

domain names are! and how a name! and its location! are looed up through a service

called the 7:S. Then routers are e&plained - how do they do their ob %hat happens

if they stop woring %hatEs a router-switch The ne&t part of the chapter loos at the

circuits used to connect e"uipment together copper! wireless and optical fibre.

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9astly! how networs are accessed is described! and security issues are dealt with

reference to Virtual $rivate :etwors and ?irewalls.

2etwor1s

ver the years! many different definitions have emerged to cover the word :etwor.

DA group of $Cs connected togetherE might be one Da fully interconnected system of

hardware with redundant circuits to provide resilienceE might be another. 'n actual

fact! a networ is something as simple as two destop computers sharing a single

printer! to something as large as the internet. %hat drives a networ is the word

DinterconnectivityE.

Diagram 21 Interc)nnecti"it'

Can one $C send data to another $C and vice versa! irrespective of how they are

actually connected together Can a computer in! say! 4ngland! download information

from another computer in China %ill the two computers be compatible Should we

need to now The answers to these "uestions are yes! yes! yes and no! in that order.

The fact that a computer made by one manufacturer can DtalE to a computer made by

a different manufacturer somewhere else in the world isnEt something ust to do with

the fact that both might use icrosoft operating systems0 thereEs a bit more to it than

that. #uried deep in the heart of the $C is a set of DprotocolsE which tae care of anyincompatibilities between different computers. 't isnEt necessary to now that theyEre

69 | P a g e



there! but it might be helpful to e&plain a little about protocols and how they wor

before continuing.

Types of comm!nications

Diagram 24 T'+es )f c)mm(nicati)ns

%henever you write a letter! you observe a protocol0 D7ear SirE ends with Dyours

faithfullyE D7ear s SmithE ends Dyours sincerelyE and so on. %e do it without

thining0 itEs what we were probably taught at school. Similarly! when we ring

someone! we have a protocol for identifying who is at the other end of the line! and

how long we spea for before finding out whether the other party has understood. %e

also now what to do if we have misheard or misunderstood what was said a sort of

error detection and correction routine using the word D$ardonE or DSorry! ' missed

that! say againE %hat do we do if we answer the phone! and find someone speaing a

language we donEt understand %e might be able to spea a few words of the foreign

language! but if we canEt! then there is no point in trying to communicate.

%hat we need in the computer field is a ind of Dlingua francaE or a common language

which is used by every computer so that any computer can communicate with any

other. That doesnEt mean that if you go to a 3apanese web site and download some

data that you will necessarily understand what it says it will still be in 3apanesecharacters! but your computer will have had no problem understanding what you

70 | P a g e



ased it to do! and no problem in understanding how to as the computer in 3apan for

the information either. This is because all computers wor to an internationally agreed

set of DprotocolsE.

#ac in the 8Fs! there was no need for protocols0 all computers were made by '#.

#y the 8BFs! many other manufacturers had entered the maret! using different

internal operating systems! and it became very clear that international

communications were here to stay. :ew email pacages became available for

e&ample utloo! utloo 4&press! 4udora 9ight! 4udora $rofessional! ail$lus!

$egasus! 9otus :otes! and others. So to enable anyone anywhere to send email to any

other computer anywhere! irrespective of whether! for e&ample! one $C used utloo

to generate an email! and another used 9otus :otes to do the same ob! some sort of

protocol was needed to carry out DconversionE wor between two dissimilar elements

of software or hardware. The 'nternational Standards rganisation ('S) got

involved! and came up with the pen Systems 'nterconnection -layer odel as the

best way of solving the problem. The code for this is embedded into the computer

operating system! and wors "uietly in the bacground.

Open systems interconnection

ne of the simplest ways of understanding the pen Systems 'nterconnection model

is to relate it to a set of envelopes several envelopes fit inside one another! until only

the largest is visible. The largest one hides all the others! and is the only one visible to

the eye. #efore we see how it wors! letEs as another "uestion. 'f you want to be

absolutely sure that any postal pacet you send to another person actually gets there!

what would you do Iou ought not to drop it into a post bo&! even though the 2oyal

ail has a good trac record of delivery0 you would send it recorded delivery or

registered post. That way you can be sure that the addressee has got it. :etwors use

the same idea0 if you want to send! say! an email to somebody! and be sure that (a) itEs

arrived! (b) itEs not been damaged in transit and (c) the whole email has been

delivered! and no part is missing! then your computer would automatically use a

system for recorded delivery this is called TC$! or Transmission Control $rotocol.Iou donEt actually see this happening0 your $C taes the appropriate action

71 | P a g e



immediately you decide to send an email. 9etEs use an e&ample. %eEll send an email

to en"uiriesQtavcom.com. This email has an attachment which consists of a %ord

document of 8FF pages of te&t. The computer we will use has 9otus :otes as its email

pacage (or DclientE! as it is usually called) and it is connected to an internal 9ocal

Area :etwor! or 9A:. %hen we clic on Dcreate mailE! and fill in the various bo&es

with subect! addressee! te&t! attachment! and so on! the S' model is already woring

away on this information. The email itself is placed inside an DenvelopeE with the type

of email pacage 9otus :otes on the front. This in turn is placed inside another

DenvelopeE with a label on the front to indicate that the contents are! in fact! electronic

mail. This label says DST$E Simple ail Transfer $rotocol. This envelope in turn

is placed inside another! which says DTC$E on the front. This is the instruction for the

recipient to acnowledge safe receipt. Since this envelope isnEt big enough to hold the

email and the 8FF pages of te&t (a TC$ envelope will only hold about <FF words! or

roughly the e"uivalent of a single A= page of te&t) the computer automatically

generates enough TC$ envelopes for the whole message! and gives each envelope a

se"uence number. So! for e&ample! the first envelope would have a se"uence number

of D8 of 8FFE! the second would be D; of 8FFE and so on. 'n this way! the recipientEs

computer nows how many envelopes it is supposed to receive! and it can therefore

as for retransmission of any missing ones. 4ach TC$ envelope is then placed inside

another envelope with the source and destination addresses on it. Since networs

donEt actually use email addresses to send information! the destination address

en"uiriesQtavcom.com - has to be changed into an address format which can be

used. This is called the 'nternet $rotocol address! or '$ address. This is automatically

done by the computer. ?inally! the '$ envelopes are put inside another set of envelopes

which are addressed to a device which will send the full message into the internet

where it will be routed to en"uiriesQtavcom.com. This device is usually called a

DgatewayE in actual fact it will physically be a router. Thin of it as your post room!

where incoming and outgoing mail is sorted for delivery.

Assuming the data successfully arrives at the Dpost roomE at Tavcom! it will be

forwarded to the $C designated to handle en"uiries. At this point! envelopes begin to

be opened. The D'$E envelope is opened to see whether it has been delivered to the

right address! and to see where it has come from. 'f that is N! then the TC$

envelopes are opened one by one to chec if they have arrived in the right se"uence

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and with their contents intact. 'f so! then the envelopes are passed to the computerEs

internal Dmail roomE where ST$ opens them and uses the information to convert

what it has received (9otus :otes) into the email pacage of the computer

at en"uiriesQtavcom.com this is icrosoft utloo. nly when all this has been

correctly done! and any missing envelopes chased up and checed! will the recipient

be advised that an email has arrived.

OS model

So letEs translate all this into the S' model. 9ayers ! > and @ are to do with the type

of email pacage (9otus) and whether it is indeed an email (ST$). 9ayer = maes

sure that TC$ is used for Drecorded deliveryE 9ayer < contains DtoE and DfromE '$

addresses! and 9ayer ; has the address of your Dpost roomE or DJatewayE. 9ayer 8

defines how! and at what speed! the data is sent from your $C to the DJatewayE over

the 9A:. To use the correct technical term! when data arrives at 9ayer <! the '$ layer!

it is loaded into an envelope which is formally nown as a D$acetE! an D'$ $acetE or

an D'$ 7atagramE.

Diagram 2 T!e la'ers )f t!e O&I

1owever! there is a problem with this analogy with respect to the transmission of

CCTV images. These must be sent and received in real time! so to acnowledge

73 | P a g e



receipt of each pacet of video information would introduce an unacceptable delay

from end to end. So there must be a way of sending information without the need for

all the checing and acnowledging which is an essential part of TC$. The answer is

to use an alternative protocol! called 57$ (5ser 7atagram $rotocol). This is

sometimes called D?ire and ?orgetE! and is the e"uivalent of the postal analogy where

letters are simply posted to their addressees without the need for acnowledgements.

any '$ cameras today have a user-selectable option for TC$ or 57$ to improve the

end-to-end delay characteristics of a networ.

9. "OUSIN#S

ntrod!ction

ost cameras are fitted with some form of protective cover for several reasons. The

common e&ception is probably in small retail establishments where the ris of damage

is slight.

nternal 0o!sings

1ousings are used internally for a variety of reasons. Sometimes it is where the need

is for the camera to be discrete. This could be in certain types of establishment where

the security of customers or members is necessary. 't may be that the impression of

intrusion of privacy needs to be subtly avoided. There are housings designed to blend

in with the decor for aesthetic purposes. These can be miniature cameras secreted in

light fittings or ventilation grills. This type of housing is often used in hotels!

museums and art galleries! shopping malls! etc.

Another range of housings is designed for covert surveillance. The intention of this

housing is that it is not a deterrent but deliberately disguised as some innocuous

common obect. They usually incorporate a miniature camera fitted with a pinhole

lens. These obects have been as diverse as $'2s! clocs! e&tractor fan controls! smoe

detectors! etc. There appears no limit to the imaginative methods of concealing

cameras.

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'ndoor cameras may sometimes have to be protected from attac and therefore fitted

in vandal proof housings. This often taes the form of a wedge shaped housing fitted

in a false ceiling with the minimum area proecting below.

The disadvantage of the wedge shaped housing is that it must be mounted facing in

the correct direction. nce fitted it is not easy to change the orientation of the camera.

This type of housing is often used when it is re"uired to view along a corridor or other

predetermined direction.

Diagram 12 1 Camera in <edge H)(sing in ;alse Ceiling

There may be situations where it is needed to have more fle&ibility in setting up the

direction the camera is viewing. This re"uirement often also needs the direction being

viewed to be discreet. The solution here is to use a type of domed housing. The dome

can be either a hemisphere or a complete sphere. The hemispherical! or half dome! can

be fitted in place of a standard ceiling tile. The camera is mounted on an adustable

platform that may be set for both angles of view and direction.

Diagram 12 4 T'+es )f Discreet Camera D)me

There are two main types of plastic used for the domes. ne is a blac acrylic

material with a less dense slot through which the camera views. The other has a

silvered coating on the inside and acts in the same as a one way mirror. %ith this type

of enclosure! there is a great deal of fle&ibility in setting the camera view. 't is alsovery easy and "uic to change the direction of view through <>FK.

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"#ternal 0o!sings

These are often called weatherproof or environmental housings. There are standards

that specify the degree of protection to be provided by enclosures. ainly these are!

#S @=F! '4C @;! 7': =F F@F. The rating of protection is defined by two digits

prefi&ed by the agreed letters '$. ('n some countries three digits are used.) The letters

stand for 'ngress $rotection! and the significance of the digits is as follows0

?irst digit0 The degree of protection that is provided with respect to persons and to

e"uipment inside the enclosure.

Second digit0 The degree of protection that is provided with respect to the harmful

ingress of water.

Third digit0 The degree of mechanical protection.

?or e&ample! a rating of '$ @= indicates class @ protection against the ingress of dust

and class = against the entry of moisture. Camera housings used in the 5N will

usually have a rating of '$ >@ or '$ >>.

:ote that these ratings only apply to normal environmental conditions. Special

protection is re"uired for areas such as refineries! mines! flour mills! etc. 'f there is

any doubt the customer will be aware of special conditions applying to particular parts

of the site. Tables 8F.8and 8F.; at the end of this chapter list all the inde& numbers.

Selection of "#ternal 0o!sings

%eatherproof housings must be about the most mundane aspect of a CCTV

installation. r so it seems! because many engineers simply consider the housing as a

protection against the elements. 1owever! there are many aspects to consider and

many suppliers of housings. 't is about the cheapest element of an e&ternal system yet

price appears to be the main factor in selecting which to use. 'mportant considerations

should be0

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4ase of access for pre-assembly in the worshop.

4ase of access during installation.

4ase of access for future service needs.

's the camera mounting plate insulated from the case

Can the mechanical focusing screw on the camera be reached Some are at the

bac! some at the side and some on top.

Can the lens be focused and the pea,average settings adusted on site

Can one man remove the cover and wor on the inside

'f there is a telemetry board fitted! can it be accessed without removing the

camera

10. EMOTE POSITIONIN# DEVICES

ntrod!ction

There are two main types of remote positioning device! those that move only in a

hori/ontal plane! and those that can move in two planes. ovement in a hori/ontal

plane is nown as panning or scanning. ovement in the vertical plane is nown as

tilting. The device that provides movement in both planes is called a pan! tilt unit or

pan! tilt drive. #oth scanners and pan! tilt units are made for indoor and outdoor use.

The construction is fundamentally the same e&cept that those units for e&ternal use are

designed for the appropriate '$ rating. (See Chapter for description of '$ ratings).

$an! tilt units are also produced for the range of ha/ardous environments mentioned inChapter 8F.

77 | P a g e



Scanners

A common type of scanner is shown in 7iagram 88.8! which may be designed for

either internal or e&ternal applications.

7iagram 88. 8 Typical Scanner 5nit

The camera may be mounted directly on the platform in usual indoor situations. The

camera mounting platform is adustable to a fi&ed position of tilt by a bolt through the

pivot. The degree of rotation is set by two movable striers that operate limit switches

at each end of the re"uired travel. These units can be set to automatically reverse

when a limit switch is operated and therefore continuously scan between the set

limits. This is called auto-pan and re"uires an additional simple board in the controlunit. The wiring is very simple and telemetry would not generally be used for

controlling this type of device. ?or e&ternal use the units are larger and made

weatherproof to the appropriate standard. They are also more powerful than indoor

models because they need to support a weatherproof housing. The camera supply and

coa&ial cables must be left with sufficient slac to eliminate strain through the

movement of the scanner. There should be enough slac cable to allow for the

ma&imum travel of the unit. Although it may be initially installed with a small degree

of scanning! re"uirements could change in the future. Typical scanning speed is >K per

second and ma&imum rotation in the order of <=@K. There is usually a minimum

rotation of @K-8FK due to the si/e of the limit stops. This type of scanner is not very

attractive in appearance especially with the slac cables going to the camera. n the

other hand it is easily seen and is often used for its deterrent value. %here aesthetics

are important or discrete mounting is needed there are other types of scanners

available. The hemispheres and domes mentioned in Chapter8F could incorporate

scanning drives.

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7iagram 88. ; 1ousings for 7iscreet Scanners

Pan3 Tilt /nits

As with scanners! pan! tilt units may be designed for either internal or e&ternal use.

There are two main types of pan! tilt unit. The first is a unit where the camera or

housing is mounted directly on a platform that forms part of the construction. There

are two types of this design where the platform is either mounted on the side of the

unit or over the top. The second type of pan! tilt unit is where the driving components

are contained within an enclosed housing.

7iagram 88. < Types of $an! Tilt 5nit

Rating of Pan3 Tilt /nits

$an! tilt units are rated by the load carrying capacity of the platform. 'n addition! over

the top units are rated by the centre of gravity of the load being within a certain

distance above the top of the platform. See comments later for load rating of over the

top units.

11. CONTOL S$STEMS AND CA%LIN#

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ntrod!ction

Telemetry is the automatic measurement and transmission of data from a distant

source to a receiving station. 'n the previous chapter! the various ways in which

cameras may be moved so that a different field of view may be obtained were

discussed. Some means of controlling these positioning devices must be used where

movable cameras are present in a system. These control systems are generally referred

to as telemetry systems. This name comes from the Jree word meter! to measure!

and therefore to control! and tele meaning at a distance! in the same way that

television means viewing an obect at a distance.

There are many types of control systems available on the maret and! as always! each

method of controlling a movable camera has its benefits and drawbacs. The purpose

of this chapter is to e&plain the principles of the various types of control systems

available and to discuss their advantages and disadvantages.

There are two main ways of configuring the cabling from a controller to remote

locations. ne is nown as daisy chain in which the cable is looped from one unit

onto the ne&t and so on. The other is a star configuration in which a separate cable is

run from the controller to each location. These types of connection only apply to the

control cable. The video cable must always be run from each camera location bac to

the main control. 'n other words! the video cable is always in a star configuration.

7iagram 8;. 8 2emote Control %iring Systems

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The daisy chain configuration does not need the last unit to be looped bac to the

controller. The control system being considered should be checed to ascertain which

method of cabling is re"uired. 'n a large industrial CCTV system! the layout of the

site will dictate which type of cabling will be the most economical.

0ard 4ired Control Systems

1ard-wired control systems are the simplest way of controlling movable cameras. As

the name would suggest the connection between the control panel and the

scanner,pan-tilt and motorised lens is direct connection by a length of multicore cable.

The cost benefits of such an approach are that no form of telemetry receiver is

re"uired at the camera location! neither is a local power supply point necessary at the

camera site as all the power for the camera! lens and pan-tilt may be sent over the

same cable. The lens functions re"uire a > or 8; volt 7C supply! which will be

provided by the controller. The pan! tilt functions may be 8; volt 7C or ;= volt AC.

A typical hard-wired camera installation might be as shown in 7iagram 8;.;.

7iagram 8;. ; Typical 1ard %ired Camera 'nstallation

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The video switching in a system lie this would be done with a simple video switcher

on to one or two monitors. As there is only one movable camera in the system! it is a

simple matter to select the picture from the movable camera on to one of the monitors!

and then to control the position and lens of that camera with the hard-wired control

panel. Typically! the cable re"uired for connection from the control panel to the

movable camera must consist of 8; individual wires! or cores! covered by an overall

sheath. This number of cores is needed! as all the functions of the movable camera

must be individually sent along the cable. A typical schedule for such a cable might

well be as follows0

CORE ;UNCTION

8 $an 9eft

; $an 2ight

< Tilt 5p

= Tilt 7own

@ $an,Tilt Common

> Uoom in

Uoom out

B ?ocus near

?ocus far

8F 1ousing washer

88 1ousing wiper

8; Common

Table 8;.8 Typical telemetry connections

There are two important factors to be considered in respect of hardwired systems.

These are the safety and cost of installing this multicore cable! the ma&imum distance

at which hardwired pan-tilts may be sited from the controller. 't is obvious to see that

the cost per metre of a 8; cored cable will be higher than the single or double pair

cable re"uired by other forms of telemetry system. This though is offset by the saving

in supplying telemetry receivers and transmitters. 'n a site where there are several

hardwired movable cameras at some distance apart! the cost of the cable may be

noticeable in the total price of the system. The second part of this concern is that there

are two main types of pan-tilt unit available! ;=-volt AC types and ;=F volt AC types.

The '44 wiring regulations state that ;=F-volt cables must be run in protective

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conduit or truning! for safety reasons. These regulations further state that low voltage

cables! such as those conductors used for lens control must not be run in the same

conduit. 'f ;=F-volt AC pan-tilts are used then all the e&pense of providing this

protection must be considered. The other limitation of hard-wired controllers is

imposed by the voltage drop caused by the resistance of the cable. The current drawn

by the pan-tilt unit causes the cable to heat and resist that current. The symptom of

this resistance is a drop in the voltage available at the pan tilt. The greater the current

drawn by the pan-tilt the greater the voltage drop! therefore the smaller the distance

that the pan,tilt can be from the controller before the remaining voltage to the pan,tilt

is too small for the pan-tilt motors to wor6 The limiting voltage drop is about 8FL of

the total! '.e. ;.= volts for a ;=-volt pan-tilt and ;= volts for a ;=F-Volt pan-tilt. hms

law enables the effect of the resistance of the cable to be calculated. This is given by

the following simple formula 0

Voltage drop O Current & 2esistance ('2 drop)

?rom cable datasheets! the amount of resistance per metre can be obtained. nce that

has been found then the resistance of the cable can be calculated. The overallresistance will be for twice the length of the run. This is because there is the resistance

of the core feeding the motor and the resistance of the return core to be considered.

The current drawn by the pan-tilt can be found in the datasheet of the pan-tilt. The

current and resistance obtained can then be put into the formula above to find the

voltage drop. 'f the voltage drop is greater than 8FL of the total then there will be

problems and a larger core of cable will have to be used. This will have a conse"uent

effect on the cost of the installation. As an e&ample! a ;F-A%J cable might have a

resistance of F.F@< hms per metre. A pan-tilt with a current consumption of F.

Amps is planned for siting ;@ metres from the controller. The total length of the

conductor will be twice ;@ metres! because of the effect of the supply and return

cores. The total resistance would be @F times F.F@< hms O ;.>> hms. The voltage

drop will therefore be F. & ;.>> O ;.= volts. This is the ma&imum that may be

tolerated. Therefore! the ma&imum cable run for hardwired control is "uite small for

;=-volt AC pan-tilts. ne option is! of course! to use ;=F-volt AC pan-tilts. The

benefits of such a choice are two fold. ?irst! the ;=F-volt pan tilt uses much less

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current that a ;=-volt pan tilt and so the voltage drop will be smaller. ?urthermore! the

8FL ma&imum voltage drop is ;= volts rather than ;.= volts and so the effect of any

voltage drop is less. 1owever! due to the wiring regulations mentioned earlier! the

additional cost of installing conduit or truning for the ;=F-volt cables must be

incurred. Some e"uipment manufacturers have approached this problem by

developing relay bo&es that are installed at the pan-tilt location. A relay bo& consists

of several low voltage relays! one for each function. The low voltage is provided from

the controller that operates a relay that switches the mains voltage to the appropriate

function. Such a system would be as shown in 7iagram 8;.<. The relay bo&es give

several advantages0

8. The relays use much less current than pan-tilts and so the voltage drop is much

less. The payoff is in operating range! up to =FFF metres6 Alternatively a

much smaller gauge! and conse"uently cheaper! cable may be used.

;. 4ither type of pan-tilt! whether ;= volt or ;=F volt! may be used at any one

camera location.

1owever! there are also two disadvantages0

8. ;=F-volt mains supply points are needed at each movable camera location to

power the relay bo&es. 't is important to remember! though! that these supply

points would also be needed with any other form of telemetry.

;. There is a cost involved in buying the relay bo&es! but these are noticeably

less e&pensive than a telemetry receiver of any other type of system.

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7iagram 8;. < 1ard %ired Control System with 2elay #o&es

The limiting factor for hard wire systems is the number of movable cameras. 't can be

confusing for the person using the system if there are! say! more than three oystics

for camera control. There are controllers available where several movable cameras!

typically si&! can be controlled from a single controller. 'n such a controller! the

operator pushes a button to select which camera is to be controlled and the control

voltages are switched to the corresponding multicore cable. The operation of such

systems is slightly awward! as the operator must remember to select the same camera

on the video switcher as has been selected on the hard wire controller. The effective

limit! then! for hard-wired systems is really one or two movable cameras.

12. MULTIPLE SCEEN DISPLA$S

ntrod!ction

Any system that combines more than one video signal is technically a multiple&er.

These days it is customary to refer to multiple&ers as e"uipment that can

simultaneously combine eight or more signals! otherwise they are nown as screen

splitters or "uad splitters.

There will be many occasions when it will be advantageous to display more than one

camera on the monitor at once. ne e&ample is if an incident occurs but it is not

certain ust where it originated. %ith a simple switching device! it would be a tedious business to review all the cameras recorded in se"uence. 'n addition! as stated

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previously! essential information may be lost. 1owever! if all the cameras were

recorded simultaneously and could be displayed simultaneously then reviewing and

finding the se"uence of events would be very much easier. 'n addition! virtually no

information would be lost and the relevant scenes can then be analysed with full

screen pictures. The essential benefit therefore of recording in the various multiple

screen formats is that no information is lost due to dwells in switching.

Analog!e and &igital &isplays

The picture received directly from a camera and displayed on a monitor is an

analogue representation of the scene. The picture information has been converted

directly to a video signal and reconverted to the same scene on the monitor. The

clarity of the picture is dependent on the "uality of the camera! the lens! the

transmission system and the monitor.

To display or record more than one picture at a time it is necessary on most systems to

convert the analogue signal to a digital form. This is nown as analogue to digital

conversion. After processing! the signal then has to be converted bac to analogue

form to be displayed on a monitor. This process introduces the possibility of

degradation to the original picture. 7efinition can be lost through the complicated

conversion processes and noise can be added to the signal. Also! the final "uality is

dependent on the resolution in terms of the number of pi&els comprising the digital

information.

Pict!re in Pict!re

This is a simple system by which one scene can be inserted in another. The camera

outputs are connected to a controller that allows one camera to be designated as the

main picture. The other camera is designated as the inserted picture. The inserted

picture may be positioned and si/ed anywhere on the screen as shown in 7iagram

8<.8. 5sually either camera may be displayed as a full screen picture.

The normal controls for the inserted picture are0 1ori/ontal si/e! vertical si/e!

hori/ontal position and vertical position. :ote that only the inserted picture may be

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altered! the bacground camera is always shown full screen. :ote that! where the

inserted picture is analogue the cameras need to be synchronised. This can be from an

e&ternal sync generator or one camera can be synchronised from the other.

7iagram 8<. 8 4&ample of $icture in $icture

Screen Splitters

This is similar to a picture in picture inserter e&cept that both camera scenes can be

adusted to compose the most useful combination. A screen splitter refers to a

combination of two cameras. The split can be arranged either hori/ontally or

vertically. The degree of overlap of either camera can also be adusted. Screen

splitters also re"uire the cameras to be synchronised.

5!ad Screen Splitters

As the name implies! this system allows the presentation of four cameras on the one

screen. The maority of "uad splitters now incorporate digital image processing. This

means that it is not necessary to synchronise the cameras and the picture is digitally

compressed to a "uarter of its si/e. The four images are then displayed on a single

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screen. :ote that each picture will only be ;@L of the screen resolution. There are

many features that may be available with "uad screen splitters and it is essential to

chec with manufacturersE literature for particular models. As always! the more

features it provides the more e&pensive a unit is liely to be. 't is possible to

7iagram 8<. ; 'llustration of uad Screen 7isplay

spend more than necessary if poor selection of a piece of e"uipment includes more

features than are re"uired. Another factor to chec out is the resolution of the

displayed pictures. Some features that may or may not be included are as follows.

Camera np!ts

#y definition! "uad splitters will have four inputs but there are units available that can

have eight inputs. These usually display blocs of four cameras in se"uence.

"lectronic +oom

%hen a camera is shown in full screen this is a method of electronically enlarging a

"uarter of the screen to a full screen view. The area in view may be DpannedE around

any part of the original picture. :ote though that this will produce a very grainy

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looing picture. This is because each pi&el in the enlarged view will be four times as

large as in the full screen scene.

?or instance! if the full screen picture is made up of @8; & @8; pi&els then a "uarter

screen will contain ;@> & ;@> pi&els. %hen D/oomedE the new full screen picture will

be made up of the ;@> & ;@> pi&els.

Se6!ential Switching

This is the capability to provide either a "uad display or se"uencing through each full

screen picture.

&!al O!tp!t

The capability of providing dual monitor outputs! one with a "uad display! the other a

se"uence display.

Alarm np!ts

Some "uad splitters offer the capability to accept alarm inputs. The treatment on

receipt of an alarm can vary. ?or instance! it can hold the associated camera on full

screen until deactivated or it could override a se"uence and switch to "uad display.

Alarm O!tp!ts

Alarm outputs are sometimes provided. These can be used to switch a video recorder

to real time or operate any other ancillary e"uipment.

Camera Titling

Another option sometimes available is the facility to insert camera numbers and titles

on the screen. These can usually be moved around the screen to prevent obscuring an

important part of the scene. :ot all systems allow the positioning of individual camera

titles. Some only provide a fi&ed position for all cameras. The number of characters

available for titles varies between models.

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$oop Thro!gh

As with switchers! some models provide loop through facilities with switchable

termination. The same comments apply to ensure correct termination when looping

through video signals.

On Screen Men!

Some of the systems with more facilities provide the capability of setting up the

various functions from on screen prompts.

Video $oss Alarm

This feature can provide a warning! both visible and audible! if there is a loss of video

signal from any of the cameras

13. LI#"T AND ILLUMINATION

ntrod!ction

The subect of the science of illumination is comple& and is not appropriate to this boo. This section is intended to provide general guidance to those aspects that affect

the performance of CCTV systems. An understanding of the principles of light is

important to the design of CCTV systems because without ade"uate light there can be

no pictures. %hat is Dade"uate lightE is dependent on many factors! some of which

have already been mentioned in the specification of cameras and lens. The most

important aspects of light affecting the design of CCTV systems are0 9ight level in

lu&0 2eflectance0 The wavelength of the light source. The light level and reflectanceare interrelated and decide the camera sensitivity. The wavelength must be related to

the spectral response of the camera.

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Principles of $ight

"lectromagnetic Radiation

9ight is energy in the form of electromagnetic radiation. The different forms of

electromagnetic radiation all share the same properties of transmission although they

behave "uite differently when they interact with matter.

7iagram 8=. 8 4lectromagnetic Spectrum

9ight is that part of the electromagnetic spectrum that can be detected by the humaneye. This is a very narrow band within the total spectrum as shown in 7iagram 8=.8.

The wavelengths used for CCTV lighting are shown and are discussed later in this

chapter. ne metre is 8!FFF!FFF!FFF nanometres (nm).

"lectromagnetic 4aves

The Transmission of light energy can be conveniently described as a wave motion and

having the following properties0

4lectromagnetic waves re"uire no medium and therefore can travel in a

vacuum.

't has been shown that different types of electromagnetic radiation have

different wavelengths or fre"uencies.

All electromagnetic waves travel at the same velocity! which is appro&imately

<FF!FFF!FFF metres per second in a vacuum.

The waves travel in a straight line but can be affected by0

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Reflectance. %hich is the reversal of direction that occurs at the

surface of an obect.

Refracti)n. A change of the angle that occurs at the boundaries of

different surfaces. 7ifferent wavelengths have different angles of refraction.

Diffracti)n. %hich is a deflection that occurs at apertures or edges of

obects.

Visible Radiation

These are the wavelengths of light that are visible to the human eye and are from

appro&imately <BF nm to >F nm. %hen all these wavelengths are seen

simultaneously the eye cannot distinguish the individual wavelengths and the result is

seen as white light. Therefore! white light is not one wavelength but a combination of

them all. This effect can be demonstrated in reverse by passing white light through a

prism. As stated previously! different wavelengths have different angles of refraction!

therefore when the light is passed through a prism it is dispersed into its constituent

spectra because each wavelength is refracted differently. The result is that if a white

screen is placed to show the light passing out of the other side of the prism it will

show all the individual colours. This effect is shown in 7iagram 8=.;. The result is to

show the spectrum of light and the seven significant colours of the rainbow. 'n reality!

there is a continuous range of hues but the eye sees mainly the main colours. A real

rainbow is created in the same way by the light being reflected and refracted by

droplets of moisture in the atmosphere.

7iagram 8=. ; 2efraction of %hite 9ight

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Spectral Sensitivity

The spectral sensitivity of cameras is described in Chapter = and this section brings

this together with considerations of the light and the nature of the light. 't should be

emphasised that the charts plot relative sensitivity. The vertical scale represents the

percentage of the rated sensitivity at different wavelengths. 't is not a measure of the

camera sensitivity in lu&. There are many installations that have been disappointing in

performance. This is due to a lac of understanding of the relationship between the

light source and the specification of the camera. ost manufacturers will provide a

spectral sensitivity diagram for their products on re"uest. 1owever! they are not all to

the same scale on each a&is and so can be confusing to mae a realistic comparison of

performance. 't is a good idea to reproduce different diagrams to one common scale

that gives a much better impression of relative sensitivity. An e&ample is shown in

7iagram 8=.< of two different sensitivity diagrams. The one on the right could easily

give the impression that it covers a wide range of wavelengths! whereas the one on the

left could convey the idea of very high sensitivity. They are in fact for identical

specifications.

7iagram 8=. < Sensitivity 7iagrams

14. TANSMISSION OF VIDEO SI#NALS %$ CA%LE

ntrod!ction

This is not meant to be a te&tboo on transmission but is intended to remove some of

the mystery associated with various methods of transmission. any appro&imations

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and simplifications have been used in writing this guide. This is to mae the subect

more understandable to those people not familiar with the theories. ?or general

application in the design of CCTV systems it should be more than ade"uate and at

least point the way to the main "uestions that must be addressed. The manufacturers

of transmission e"uipment will usually be only too een to help in final design.

This first part deals with the transmission of video signals by cables. $art ; deals with

the transmission of video signals by other methods such as microwave! telephone

systems! etc. See chapter for transmission over networs in more detail.

7iagram [email protected] ethods of Transmitting a Video Signal

7iagram [email protected] illustrates the many methods of getting a picture from a camera to a

monitor. The choice will often be dictated by circumstances on the location of

cameras and controls. ften there will be more than one option for types of

transmission. 'n these cases there will possibly be trade offs between "uality and

security of signal against cost. This diagram could now include transmission by '$

metwors.

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-eneral Principles

Video Signal

The essential components of the video signal are covered in Chapters two and three.

Certain aspects that are related to the effective transmission of those signals are

repeated in this chapter where it is necessary to save continuous cross-reference.

Synchronising

The video signal from a TV camera has to provide a variety of information at the

monitor for a correct TV picture to be displayed. This information can be divided into0

Synchronising pulses that tell the monitor when to start a line and a field video

information that tells the monitor how bright a particular point in the picture should

be chrominance that tells the monitor what colours a particular part of the picture

should be (colour cameras only).

%andwidth

The composite video output from the average CCTV camera covers a bandwidth

ranging from ;@1/ to @1/. The upper fre"uency is primarily determined by theresolution of the camera and whether it is monochrome or colour. ?or every 8FF lines

of resolution! a bandwidth of 81/ appro&imately is re"uired. Therefore! a camera

with >FF lines resolution gives out a video signal with a bandwidth of appro&imately

>1/. This principle applies to both colour and monochrome cameras. 1owever!

colour cameras also have to produce a colour signal (chrominance)! as well as a

monochrome output (luminance). The chrominance signal is modulated on a

=.=<1/ carrier wave in the $A9 system therefore a colour signal! regardless of

definition! has a bandwidth of at least @1/.

Re6!irements to Prod!ce A -ood 5!ality Pict!re

?rom the above it will be obvious that to produce a good "uality picture on a monitor!

the video signal must be applied to the monitor with little or no distortion of any of its

elements! i.e. the time relationship of the various signals and amplitude of these

signals. 1owever in CCTV systems! the camera has to be connected to a monitor by acable or another means! such as ?ibre ptic or microwave lin. This interconnection

95 | P a g e



re"uires special e"uipment to interface the video signal to the transmission medium.

'n cable transmission! special amplifiers may be re"uired to compensate for the cable

losses that are fre"uency dependent.

Cable Transmission

All cables! no matter what their length or "uality! cause attenuation when used for the

transmission of video signals! the main problem being related to the wide bandwidth

re"uirements of a video signal. All cables produce a loss of signal that is dependent

primarily on the fre"uency! the higher the fre"uency! the higher the loss. This means

that as a video signal travels along a cable it loses its high fre"uency components

faster than its low fre"uency components. The result of this is a loss of the fine detail

(definition) in the picture.

The human eye is very tolerant of errors of this type a significant loss of detail is not

usually obectionable unless the loss is very large. This is fortunate! as the losses of

the high fre"uency components are very high on the types of cables usually used in

CCTV systems. ?or instance! using the common coa&ial cables 52F or 2J@!

@FL of the signal at @1/ is lost in ;FF metres of cable. To compensate for these

losses! special amplifiers may be used. These provide the ability to amplify selectively

the high fre"uency components of the video signal to overcome the cable losses.

Cable Types

There are two main types of cable used for transmitting video signals! which are0

5nbalanced (coa&ial) and balanced (twisted pair). The construction of each is shown

in diagrams 8@.; and 8@.<. An unbalanced signal is one in which the signal level is a

voltage referenced to ground. ?or instance! a video signal from the camera is between

F.< and 8.F volts above /ero (ground level). The shield is the ground level.

A balanced signal is a video signal that has been converted for transmission along a

medium other than coa&ial cable. 1ere the signal voltage is the difference between the

voltage in each conductor.

4&ternal interference is piced up by all types of cable. 2eection of this interferenceis effected in different ways. Coa&ial cable relies on the centre conductor being well

96 | P a g e



screened by the outer copper braid. There are many types of coa&ial cable and care

should be taen to select one with a @L braid. 'n the case of a twisted pair cable!

interference is piced up by both conductors in the same direction e"ually. The video

signal is travelling in opposite directions in the two conductors. The interference can

then be balanced out by using the correct type of amplifier. This only responds to the

signal difference in the two conductors and is nown as a differential amplifier.

/nbalanced 'Coa#ial( Cables

This type of cable is made in many different impedances. 'n this case impedance is

measured between the inner conductor and the outer sheath. @-hm impedance cable

is the standard used in CCTV systems. ost video e"uipment is designed to operateat this impedance. Coa&ial cables with an impedance of @ hms are available in

many different mechanical formats! including single wire armoured and irradiated

$VC sheathed cable for direct burial. The cables available range in performance from

relatively poor to e&cellent. $erformance is normally measured in high fre"uency loss

per 8FF metres. The lower this loss figure! the less the distortion to the video signal.

Therefore! higher "uality cables should be used when transmitting the signal over

long distances. Another factor that should be considered carefully when selecting

coa&ial cables is the "uality of the cable screen. This! as its name suggests! provides

protection from interference for the centre core! as once interference enters the cable it

is almost impossible to remove.

7iagram 8@.; 5nbalanced Cable

%alanced 'Twisted Pair( Cables

'n a twisted pair each pair of cables is twisted with a slow twist of about one to two

twists per metre. These cables are made in many different impedances! 8FF to 8@F

hms being the most common. #alanced cables have been used for many years in the

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largest cable networs in the world. %here the circumstances demand! these have

advantages over coa&ial cables of similar si/e. Twisted pair cables are fre"uently used

where there would be an unacceptable loss due to a long run of coa&ial cable.

7iagram 8@.< #alanced Cable

The main advantages are0

8. The ability to reect unwanted interference.

;. 9ower losses at high fre"uencies per unit length.

<. Smaller si/e.

=. Availability of multipair cables.

@. 9ower cost.

The advantages must be considered in relation to the cost of the e"uipment re"uired

for this type of transmission. A launch amplifier to convert the video signal is needed

at the camera end and an e"ualising amplifier to reconstruct the signal at the control

end.

mpedance

't is e&tremely important that the impedances of the signal source! cable! and load are

all e"ual. Any mismatch in these will produce unpleasant and unacceptable effects in

the displayed picture. These effects can include the production of ghost images and

ringing on sharp edges! also the loss or increase in a discrete section of the fre"uency

band within the video signal.

The impedance of a cable is primarily determined by its physical construction! the

thicness of the conductors and the spacing between them being the most important

factors. The materials used as insulators within the cable also affect this characteristic.Although the signal currents are very low! the si/es of the conductors within the cable

98 | P a g e



are very important. The higher fre"uency components of the video signal travel only

in the surface layer of the conductors.

7iagram 8@.= Transmission 'mpedance.

?or ma&imum power transfer! the load! cable and source impedance must be e"ual. 'f

there is any mismatch! some of the signal will not be absorbed by the load. 'nstead! it

will be reflected bac along the cable to produce what is commonly nown as a ghost

image.

15. TANSMISSION OF VIDEO SI#NALS %$ EMOTE

MET"ODS

ntrod!ction

The previous chapter dealt with the transmission of video signals by various types of

cable. There are many instances where it is not possible or desirable to use cable and

other methods need to be employed. These can be0

'nfrared beams.

icrowave.

$ublic telephone networs.

1igh Speed 7ata 9ins

9ocal Area :etwors (9A:)

%ide Area :etwors (%A:)

ptical fibre cables.

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The choice will depend on the final system re"uirements. This may fre"uently be

coupled with the different cost of several options. 'n addition! the level of security and

continuity of use will have a bearing on the final selection.

%ith all these systems! it is imperative to study the supplierEs information e&tremely

carefully. ?or instance! there was a slow scan system that described the picture update

time as ;F seconds full picture! @ seconds "uad display. %hat this really meant was

that in "uad display one picture was updated every @ seconds. 't still too ;F seconds

until the first picture was refreshed6 %herever possible see a demonstration of a

system on a customerEs premises. 9oo carefully at the resolution versus the refresh

time.

*ree space transmission

There are fre"uent situations where there is no possibility of maing a direct cable

connection between the camera(s) and the control position. This particularly applies

when real time continuous monitoring is re"uired. A situation needing this approach

would be where! for instance! there is a main road between the cameras and the

control.

Another situation would be when the two ends of the system are separated by a wide

river such as in 9ondon. 't could be a large industrial site where the cost of cabling

would be prohibitive.

?ree space transmission consists of a transmitter at the camera end and a receiver at

the control end. All free space transmission systems re"uire that there be a direct line

of sight between the transmitter and the receiver. :ormally there are one transmitter

and one receiver for each camera. A typical application is shown in 7iagram 8>.8.

All types of free space transmission e"uipment must be very rigidly mounted. This is

especially important if the transmitters or receivers are to be mounted on masts or

poles.

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The distance between the two locations is critical to the choice of e"uipment. The

manufacturerEs specification must always be respected. $erformance can deteriorate

e&ponentially if their recommendations are e&ceeded. A 8FL increase in distance

could result in a <FL fall off in performance.

7iagram 8>. 8 Application ?or ?ree Space 9in

There will be situations where there are several units re"uiring surveillance all

controlled from a central source. Jreat care should be e&ercised in positioning

receivers so that there is suitable separation between the beams from transmitters.

7iagram 8>. ; 5nsuitable 9ocation of 2eceivers

'f the e&ample site in 7iagram 8>.8 re"uired a second camera to be incorporated! this

would need another transmitter and receiver. 'f they were simply added as shown in

7iagram 8>.; there is a strong probability that the beams would overlap at the

receivers. This would cause problems with the reception of the separate video signals.

There are ways in which different systems can overcome this. 1owever! a little

thought can prevent the need for special considerations. An alternative method of

siting the receivers is shown in 7iagram 8>.<.

'f the receivers are located as shown there will be no chance of cross interference

between the two signals.

101 | P a g e



7iagram 8>. < $referred ethod of 9ocating 2eceivers

There is one very important point to consider when setting up any type of free space

transmission system. The manufacturers recommended test e"uipment must be used

to align the pairs of units. 'f the width of the beam is only 8 degree! this is a width of

over 8 metres at a distance of one ilometre. any installers have mistaenly

thought that since the receiver is within this band then the reception will be

satisfactory.

ost systems will be aligned on a clear day when it is not raining and during daylight.

Therefore! the reception will seem fine. A slight deterioration in the weather could

reduce the performance considerably after the engineers have left site. 'rrespective of

the beam width! it should be emphasised that the main signal strength is in the centre

part. nly the correct test e"uipment will ensure that the system will be set up to its

optimum for all conditions.

nfrared %eams

%ith this type of system! the video is superimposed onto an infrared beam by a

transmitter. The beam is aligned to strie a receiver where the signal is transmitted as

a conventional composite video signal. The infrared beam is at a wavelength of B>F

nanometres which! from Chapter 8=! can be seen to be beyond the visible part of the

spectrum. The system may be configured as a full duple& set up. Then it is possible to

transmit telemetry control signals in the reverse direction to control pan! tilt units. The

system can also carry speech in both directions. The actual configuration must be

specified at the time of obtaining "uotations or ordering.

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The performance of infrared beams can be affected by weather and environmental

conditions. 't is important to chec the capability of the lin with the manufacturer if

an absolute guarantee of reception in all conditions is essential.

The infrared beam is completely harmless and re"uires no licence or operating

restrictions. Selecting the correct beam power for a given range re"uires some

consideration. There is always a trade off between range and "uality. ne

manufacturer! for e&ample! gives the following guidelines. (Table 8>.8)

5nder each model the range is given in metres for each re"uirement.

Re/(irement -)del A -)del B -)del C -)del D -)del E

(8) 4conomy "uality 8F 8F 8;;F ;<@F <8FF

(;) ?ull "uality 8;F <;F >;F 8;FF ;8FF

(<) 1igh penetration <F 8>F <FF @F 8;FF

(=) 1igh resolution BF ;@F <F @F 8B;F

(<) W (=) together - 8;F ;@F >FF FF

Table 8>. 8 2ange f 'nfrared 9ins

This table illustrates the problem of selecting the most appropriate model for a

particular application. ?or instance! the model specified as having a range of <!8FF

metres only provides Deconomy "ualityE at this range. 'f high resolution and high

penetration are re"uired then the range drops dramatically to only FF metres.

%ithout this information! it is very difficult for a customer to compare competing

"uotations all specifying Dinfrared linsE. There is a significant price ump from one

model to the ne&t.

't can also be seen from the table that infrared lins are susceptible to poor weather

conditions. 't is important therefore that both the installer and the customer are aware

of the limitations of this type of lin. ne argument is that if the cameras are installed

outdoors then by the time the lin has failed due to bad weather the camera picture

has also failed. This is a doubtful basis on which to specify a system. There are two

factors that have caused problems in the past with this type of lin. #oth were

intermittent and difficult to figure out the cause of lost pictures in apparently good

weather conditions. ne was a steam vent outlet that caused the steam to carry

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through the beam in certain wind conditions. The other was smoe from a

chimneystac that obscured the beams also only in certain wind conditions. :either of

these effects was in the sight of the cameras.

Another important point is that the beam width of infra-red lins is very small! in

order to ensure that enough of the infrared beam falls on receiver to give a good signal

to noise ratio. Typically! at a distance of 8@FFm the spot of infrared light shone on to

the receiver may only be a couple of metres in diameter. Conse"uently! over longer

distances above @FFm! minute changes in the position of the transmitter may cause the

beam to be thrown completely off the receiver and transmission will be lost. This is

particularly important if the transmitter is mounted on a steel fabricated building such

as a warehouse or hanger. Steel buildings will e&pand and contract with temperature

change and these tiny changes may be enough to adversely affect the position of a

transmitter mounted on a steel building.

'nfrared lins! however! do offer a cost-effective solution to free space transmission.

The full nowledge of their possible limitations should be considered. There is no

re"uirement for any form of licence for an infrared lin.

Microwave Transmission

icrowave lins carry the video and telemetry along a lin from a transmitter to a

receiver. They are capable of much farther transmission distances from 8 ilometre to

BF ilometres. The fre"uencies that can be used in the 5N are allocated by The

2adiocommunications Agency! they also determine the ma&imum power that may be

transmitted! which limits the operational distance. They are largely unaffected by

weather conditions. n the other hand! they are more e&pensive than infrared lins.

Similar comments apply that mountings must be rigid and the correct test e"uipment

must be used for installation. #eam width is wider than infrared systems and so

building movement is not normally a problem.

7uple& systems can be provided where it is re"uired to operate telemetry controls in

the reverse direction. This must be specified at the time of "uotation or order.

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The re"uirement for licences should be checed with the manufacturer to find the

total cost of a system and any recurring costs. 'nvestigation will need to be carried out

if microwave lins are to be used close to other microwave e"uipment such as radar at

airports as it will be vital that no interference affects the performance of either system.

16. TANSMISSION OF VIDEO SI#NALS %$ FI%E OPTICS

Principles of *ibre Optic Transmission

ost people are familiar with the everyday use of light! X-rays! radio waves!

microwaves! and 2adar. All of these are actually e&amples of electromagnetic

radiation! which is characterised by a radiation wavelength or oscillation fre"uency.

7iagram 8.8 shows the electromagnetic spectrum with application areas identified.

The =FF - @F nm region of the spectrum is the region of visible light this region is

e&panded in the lower part. The area of interest for fibre optic transmission e&tends

from the red region of the spectrum out into the wavelengths much longer than those

visible to the human eye! the infrared. Specific wavelengths used have been driven by

the re"uirements of the fibre technology and by source and detector technologies.

$articular wavelengths used are nominally BFnm! B@Fnm! 8<8Fnm! and 8@@Fnm.

7iagram 8. 8 The electromagnetic spectrum

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The different parts of the spectrum have previously been described in terms of the

wavelength. An alternative measurement is the fre"uency of the part being

considered. ?re"uency is the number of crests of a wave that move past a given point

in a given unit of time. The most common unit of fre"uency is the hert/ (1/)!

corresponding to one cycle per second. The fre"uency of a wave can be calculated by

dividing the speed of the wave by the wavelength. Thus! in the electromagnetic

spectrum! the wavelengths decrease as the fre"uencies increase! and vice versa.

?or e&ample! the wavelength of infrared light is B@F nm the e"uivalent fre"uency is

<.@ & 8F8= 1/.

7iagram 8. ; #andwidth at 7ifferent ?re"uencies

7ifferent fre"uencies have different bandwidths and the higher the fre"uency the

wider is the bandwidth. The wider the bandwidth then the more information can be

carried. ?re"uencies above the visible part of the spectrum offer a wider bandwidth!therefore they provide more space for the multiplicity of TV signals and reams of data

that need to be transmitted.

Transmission by $ight

'n fibre optics! messages whether data or video are first converted from electrical

impulses into pulses of light. This function is performed by a minute device that

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incorporates a laser chip or an 947 (light emitting diode). The infrared light is

switched on and off at incredibly high speeds! thereby creating the stream of light

pulses. These are then focussed onto the end of the optical fibre. The lightwaves travel

along the fibre to the receiving end. 1ere the light pulses are converted bac into

electrical pulses by a photodiode or avalanche photodiode.

7iagram 8. < #asics of ?ibre ptic Transmission

Optical *ibre Str!ct!re and 7$ight -!iding8

An optical fibre is a comple& strand of silica glass. A cross section of a typical fibre is

shown in diagram 8>.=.

Very small units of length are measured in DmicronsE. ne micron is one millionth of a

metre! therefore! 8 micron is F.FF8 mm and 8;@ microns is F.8;@ mm.

7iagram 8. = Construction of single optical fibre

The optical fibre is made from a rod of highly purified silica called a Gpre-formH. The

pre-form is heated and drawn out into a thin fibre using highly specialised and

accurate e"uipment. As the fibre is drawn! it is coated with a protective polymer layer

nown as the primary coating. At this stage the coated fibre is appro&imately F.;@ mm

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diameter and is fle&ible enough to be coiled on drums with a bend radius of not less

than @ cm. 'n most fibres in use today the diameter of the glass fibre itself is 8;@

microns, F.8;@ mm. This primary coated fibre is then used as the building bloc for

assembly into optical fibre cable that provides the ruggedisation needed for everyday

use.

The optical fibre itself has internal structure with the refractive inde& of the fibre

varying across its diameter with all fibres having a lower refractive inde& on the

surface than at the centre of the fibre. This variation in refractive inde& across the

fibre diameter is the ey to the transmission of light by the fibre. 2emembering school

physics e&periments! when light passes from a high to low refractive inde& media e.g.

glass to air! some of the light ray is reflected and some is refracted out of the high

refractive inde& media. As the angle of the light ray to the surface gets shallower!

there comes a point where all of the light is reflected and no light is refracted out of

the media. This angle (to the normal) is called the Critical Angle above which all light

is reflected optical fibre transmission uses this effect to transmit light along the fibre.

'n diagram 8.@! the optical fibre structure is assumed to consist of a high refractive

inde& glass core surrounded by a low refractive inde& glass cladding. 9ight rays are

incident on the fibre end from a light source entering the fibre core over a range of

incident angles. nce in the fibre these rays can be considered to be travelling in

straight lines until they meet a refractive inde& discontinuity. At this point! some of

the ray is reflected bac into the fibre core and the rest is refracted out of the core into

the cladding glass. The reflected light ray then transits the fibre core until another

reflection occurs and the refracted ray hits the cladding glass,protective polymer

cladding interface and is absorbed or dispersed. As this is concerned with light

propagation down the fibre length it is clear that the reflected ray is the one that we

re"uire for signal transmission! with the refracted ray simply reducing the transmitted

light signal intensity.

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7iagram 8. @ Step inde& multi-mode fibre

Consider a continuum of light rays in the fibre core covering all possible angles of

incidence to the core,cladding discontinuity! then it can be seen that all light rays with

an angle of incidence above the critical angle will be reflected bac into the fibre core.

This is nown as Gtotal internal reflectionH. Those rays with an angle of incidence

below the critical angle will be partly reflected and partly refracted in the manner

e&plained above. The light rays transit along the fibre by being reflected at each

refractive inde& change that they encounter in effect the rays bounce off of the sidesof the fibre core.

After multiple reflections the rays with angles of incidence below the critical angle

will have been reduced in intensity by refraction losses and do not contribute to the

light! and hence signal! transmission process. 'n contrast! the rays with angles of

incidence above the critical angle will not be reduced in intensity by refraction and it

is these rays that enable fibre optic transmission to wor. As the angle of incidence is

measured with respect to the normal to the relevant surface it can be seen that the

fibre could be bent and twisted and still allow light to be transmitted along its length.

This ability of optical fibre to guide light along a non-linear path! ust lie and

electrical conductor! is essential for its use in real world applications.

This range of rays may be traced bac to their original coupling to the fibre core and

we find that the transmitted rays are contained in a cone of angles as shown in

diagram 8.@. 'n defining optical fibre parameters this acceptance cone is

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characterised by the cone half angle and the Sine of this half angle is nown as the

fibre :umerical Aperture :.A.

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17. VIDEO MOTION DETECTION

ntrod!ction

There are many methods of detecting intruders into premises. These include suchsystems as0

'ntruder alarms.

?ence mounted detectors.

#uried vibration or electric field devices.

Active infrared devices.

$assive infrared devices.

icrowave devices.

Video motion detection devices.

This chapter is concerned with Video otion 7etection devices. (V7). These may

be within or outside the premises and! besides detecting intruders! can be used as part

of a building management system. V7 may often be used either as a stand-alone

system or integrated with other detection systems. 'n an ideal world! detection devices

would give no false alarms and 8FFL of genuine alarms. 5nfortunately! this is not an

ideal world! and a certain amount of compromise is necessary. This compromise must

be reduced to the most effective and acceptable level to achieve the system obectives.

There are really only two types of alarm! genuine alarms and false alarms. Sometimes

mention is made of Dspurious alarmsE! une&plained alarms and system failures. These

must only be considered as false alarms because the system has alarmed for no

apparent reason. A genuine alarm is one created by deliberate nefarious human action!e.g. by movement of a person or vehicle into the detection field or disturbance of the

111 | P a g e



alarm system. A false alarm is one that has no deliberate human input! such as those

caused by animals! birds or any malfunction of e"uipment. ne measure of the

efficiency of a system is the D?alse Alarm 2ateE (?A2). This is the ratio of false alarms

to a time scale! i.e. five per day. The ?A2 level will depend on many local site

considerations. The obective is to reduce this to the minimum without missing any

real alarms. Another measure is the Dprobability of detectionE ($7) rate! which is the

ratio of detections to the number of attempts in controlled tests. The ideal for $7 is

8FFL.

/ses of VM&

The primary function of a V7 system is to relieve CCTV operators from the stress

of monitoring one or many screens of information that may not change for long

periods. The V7 system will be monitoring all the cameras in its system! and only

reacting when there is suspicious activity in one of the scenes. 7uring the long

periods of inactivity the operator can continue with other tass! secure in the

nowledge that when something occurs the system will immediately respond. 4ven a

moderate si/ed system! with eight cameras! would prove impossible for an operator to

monitor. 4ight monitors could not be viewed with any degree of concentration for more than about twenty minutes. 'f the monitors were set to se"uence! then activity on

seven cameras is lost for most of the time and would be totally ineffective to detect

intruders. %ith more cameras in a system! the tas of detecting intruders becomes

impossible and technology must tae over the strain.

The idea of V7 systems is that the processor is continuously monitoring all the

cameras in the system. 7uring this time! the! operator may select or se"uence cameras

using the conventional switching system. The system may include an additional

monitor connected to the V7 system that will normally show a blan screen. %hen

activity in any camera occurs that the V7 system interprets as an intruder! the

alarmed camera is immediately switched to the blan monitor and a warning sounded

to alert the operator. The operatorEs attention! is therefore! immediately focused on the

camera covering the alarm. The detection of an intruder can also set off further events!

such as setting a video recorder to real time recording! setting a matri& switching

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system to se"uence through a specific series of cameras! etc. The operator can analyse

the scene and tae the appropriate course of action.

An intruder could generate an alarm and be out of view of the camera before it is

displayed. The operator would therefore see ust a blan screen and be unsure about

what to do ne&t. To overcome this! at the time of detection! many V7 systems will

capture an alarm image se"uence containing one or more free/e frames. This may be

displayed as the first view on the previously blan screen. The operator may then

e&amine the scene at the instant of alarm in more detail.

Principle of operation

'n the descriptions that follow reference is made to a DframeE of video. Some systems

use frames and some use fields! some systems can select between the two. This also

applies to storage devices. ?or ease of description! the term frame is used for

consistency but the actual method used should be checed for the system being

considered.

Video otion 7etection is an electronic method of detecting a change in the field of

view of a camera. 'n its simplest form! this is achieved by storing one frame of the

video information and then comparing the ne&t frame with this to decide whether

there has been a change. The change detected would be a difference in the video

voltage! indicating a change of brightness within the scene. This would be initially

ignored as an alarm until a further frame confirmed the change! or not. 'f confirmed as

a change of brightness in the scene! then an alarm would be generated. This could

cause a contact to close and activate some warning device such as a bu//er! or cause

the switcher to select the camera that detected the motion. The sampling process may

tae somewhere between one fiftieth of a second and one second to detect a change!

depending on the method of sampling. This simple detector could be used in an

environment where all conditions were absolutely stable and the only possible change

in brightness would be due to an intruder. 1owever! the intruder could be a mouse or

a person. The system couldnEt differentiate between the two. 'n addition! by the time

the alarm is displayed on a monitor! the cause of it could be out of view. 'f the scene

were being continuously recorded! the event could be reviewed but this may be toolate to tae effective action.

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7iagram 8B.8 $rinciples of video motion detection

&etection Cells

?or the purposes of this chapter the following definitions are used although there are

no standard terms used at present. A CE66 is a single detection bloc that is analysed

electronically for brightness changes. A cell may be a single pi&el! a bloc of pi&els!

or the whole screen. A ONE is a group of cells that have been defined as an active

area. The e&act meaning of D/oneE must be checed with a manufacturerEs

specification before assuming what area is covered and to what degree of definition.

This method of comparing complete frames therefore has severe drawbacs. The ne&t

development was to divide the picture into a number of separate areas or cells. This

was refined by being able to switch cells on or off to define the area of the scene that

is of interest. 7iagram 8B.= illustrates a V7 system that divides the picture into

cells! and how only a selected part of the scene can be set for motion detection. The

shaded areas are inactive and the clear parts are the active cells. 'n this case! only

activity in the area of the car will create an alarm. The cells are only displayed as such

during setting up the system. nce the set-up mode is e&ited! the complete picture is

displayed as normal and it is not possible to see any of the cells.

The sensitivity of the cells can be adusted to tae into account local conditions. This

control though is applied across all cells to the same e&tent. Some systems can be pre-

set to different sensitivity levels! for instance! to mae allowance for day or night

operation when the lighting levels may be different.

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7iagram 8B. ; ?rame 7ivided 'nto Cells

This type of system would not be suitable in the scene shown out of doors. This is

because e&ternal light conditions are changing fre"uently. Clouds moving across the

sy would cause changes in brightness and create alarms. This type is used in simple

indoor situations! where the lighting conditions are constant and anything breaing the

cells could be considered an alarm. The set-up can be refined to reduce unwanted

activations. ?or instance! there may be two doors in the scene! only one of which

needs to be monitored. 'n this case! the part of the scene of interest could be adusted

accordingly. :ote that with this type of system any change in any one or all the cells

will create an alarm.

ntelligent Cells

The ne&t move towards reducing false alarms is to build in the computing power to

process each cell individually and create algorithms that will intelligently analyse

certain situations. 'n this way! decisions can be made according to the direction of

movement. ?or instance! one cell may be declared as a pre-alarm cell and another as a

detection cell. $re-alarm cells do not create alarms. 'nstead! they instruct the system to

associate detection in this area with detection in another. Activation of detection cells

alone will not create an alarm. A combination of successive detection in adacent cells

will trigger a logical action dependant on the program. ?or e&ample! if a detection cell

is activated after a pre-alarm cell an alarm will be created. 1owever! movement in the

reverse direction! detection before pre-alarm! will not create an alarm. 'n this way! all

persons leaving a building will not create an alarm but persons approaching it will doso. Also! persons moving down the right of the perimeter will not create an alarm.

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Cell Co!nt

Another factor that could be calculated in the processor is the number of cells caused

to change simultaneously. This would then be used as a further part of the e"uation! so

that an alarm would only be created if more than D&E cells change contrast

simultaneously. This brings in attendant problems in some situations. Three dogs in

the scene could activate the same number of cells as one person. A maor problem

with cell count is that of the different number of cells a certain si/e of obect occupies

in relation to the position of the camera.

7iagram 8B. < 'ntelligent cells

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7iagram 8B. = $roblems of $erspective

7iagram 8B.= shows that a person in the foreground occupies eight cells while one in

the bacground is less than half a cell. Similarly! a cat close to the camera would

activate far more cells than a person in the bacground. Simple cell count systems

may offer some improvement in false alarms but do not offer accurate si/e

discrimination.

Contrast $evels

't was stated that the detection of movement was obtained by measuring the changes

in video level (brightness) between successive frames. This is fine if a person in a

dar suit passes through a very bright scene. The change in brightness will be

dramatic and immediately evident to the processor. 1owever! a person in a grey suit

in a grey scene! with little contrast! will cause only a small change in the brightness

levels. 'f the sensitivity of the system were set to detect the latter event! it would be

over responsive to insignificant changes in a bright scene. This is less important for

indoor systems! but a significant factor in e&ternal systems where the light changes

fre"uently and greatly. 'n addition! where the obect is smaller than the cell! the

brightness change will be a function of both the si/e of the obect and the contrast

between the obect and the bacground. This becomes especially critical when

detecting a person in the bacground when they may be only 8FL of the screen

height. This can be only F.;@L of the screen area. 'f the person is substantially

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smaller than the cell! the sensitivity would have to be very high to detect this change!

but would cause many false alarms for larger subects providing greater contrast!

although much smaller than a person.

Another problem with measuring brightness using large cells is that a small dar

obect such as a cat could cause the same brightness change as a large low contrast

obect such as a person.

Camera Sha1e

'n e&ternal systems! cameras are mounted on bracets or towers. 't is often

impractical to ensure that they are absolutely rigid with no movement. The camera

would only have to move a small amount! such as can happen in the wind! to cause a

global change and register an alarm.

Changes n $ight $evels

#y processing separate cells and having the power to define better algorithms! other

problems can be overcome. ?or instance! light changes may be ignored if all cells are

affected to the same e&tent. Another method to allow for global light changes is to

mae one reference cell in which movement is unliely. The other cells are then

referenced to this to compensate for light levels. This latter method can impose

limitations on the system set-up and is now infre"uently used.

Cell Sensitivity

All the systems described so far have only been able to set the overall sensitivity of all

cells. This renders them "uite unsuitable for outdoor use. The ne&t need therefore is to be able to adust the sensitivity of each cell individually. This obviously re"uires

much more computing power but is an absolute prere"uisite for any V7 to be used

e&ternally.

Processing Speed

ost simple V7 systems have one processor irrespective of the number of cameras.

'f it re"uires three frames to analyse a scene then the processing time for one camera

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will be about F.8; seconds. This must be multiplied by the number of cameras in the

system. Therefore! with eight cameras the processing speed for each will be about one

second. ?or e&ample! a 8,;H camera with a ;@mm lens has a width of view of about

@m at ;Fm from the camera. A person could run across this field of view in less than

the processing time and not be detected.

$imitations of Simple VM& Systems

The previous e&amples have served to show the principles of simple video motion

detectors. Variations of these types are still available but their use is limited! and they

should be used with great caution in anything but the most basic applications.

1owever! they do have uses and can provide a very cost-effective method of motiondetection when the situation is appropriate.

The limitations of the types described for demanding e&ternal situations are as

follows.

%ill not cope with moderate changes in light levels.

Sporadic generation of alarms in high contrast scenes.

%ill not cope with changing weather conditions.

9ac of si/e discrimination means compromise in setting up.

:on-uniform sensitivity with range.

%ill not cope with si/e variation due to perspective.

Slow processing speed can miss moving action.

'nability to discriminate between small high contrast dar and large low

contrast obects.

$rone to false alarm due to camera shae.

Cell measurements prevent accurate area discrimination.

2estricted to small areas of view.

5nliely to detect a person at 8FL of screen height.

nly simple algorithms can be computed.

Cannot distinguish between a person moving in a line and a waving obect.

Single processor increases time between frame comparisons.

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18. INTEFACIN# !IT" OT"E S$STEMS

ntrod!ction

CCTV Systems are rarely used as the single means of security at any site. This is a

wise approach! as CCTV cannot on its own provide total security for any location.

There is very little point in having a system that enables intruders to be observed or

miscreants identified if this does not actually prevent loss or damage to the property

of the owner of the site. At the very minimum there must be good mechanical security

with good "uality doors! locs! fences and other barriers to physically prevent

undesirables from gaining access to secure areas.

?or insurance purposes! there must nearly always be some form of intruder detection

and alarm system. %ith the growth and reduction in relative cost of telephone lines

these intruder alarms are normally connected to some ind of central monitoring

facility! called a central station! where responses to alarms are co-ordinated and from

where the $olice or other security agencies are summoned. 'ntruder alarm systems

form the bacbone of electronic security! from the smallest retail site to the largest

industrial! commercial or governmental establishments.

A second mandatory electronic system present on sites is the fire alarm system. ?ire

alarm systems are installed for both insurance and building regulations purposes.

'ncreasing use of electronics in the controls of these systems has meant that they have

become more sophisticated and more reliable while at the same time offering many

more features.

1aving a site that is safe and secure outside business hours is vital. 1owever! it is of

little benefit during woring hours! when access control to a building or site may be

rela&ed to enable the employerEs staff to come and go. Thieves or vandals can also

come and go at will. 't is for this reason that access control systems have started to

become increasingly common. The simplest form of access control is a security guard

checing the identification passes of those who are entering and leaving the site. 'n

the highest security sites! this method is still used! due to the efficacy of human beings

in recognising people and determining whether they should be allowed entry.

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1owever! due to the cost of manned guarding and the dramatic reduction in the real

cost of microprocessor based electronic systems over the last few years electronic

access control systems are becoming more common. 'n these systems! the individuals

who are permitted to enter various areas of a site carry some ind of toen that is

presented to an electronic reader. The control electronics then identifies this toen and

loos into electronic memory devices. 'f the individualEs toen is valid for that entry

point then an electric loc will be released for a short time to allow entry. therwise!

access will be denied and an alarm message may be displayed on the system control

terminal. The technologies available for the toens are myriad from simple magnetic

stripe cards similar to banersE cards through to specialised high security cards!

special eys! eypads! and even palm print readers.

n large sites there may be a very long length of fencing which can be a problem to

protect at all times! within the limits that are available with manned guarding. 't is!

however! important to protect this perimeter in commercial and industrial sites to

prevent theft and vandalism! and in governmental sites to meet these as well as

terrorist and other threats. As with access control the best form of perimeter protection

is manned guard posts. This is! however! very e&pensive and conse"uently this

techni"ue tends to be reserved for the highest security sites.

7ue to this fact! various electronic devices have been developed to detect intruders

crossing the perimeter. ne group is seismic wires installed in the fence material!

which detect cutting and climbing of the fence structure. Another group of seismic

detectors are buried directly in the ground and detect the footsteps of intruders

crossing the perimeter! the alarms being signalled by cable or radio lin. 9ong range

passive infrared detectors are also used. These sense the body heat of intruders

crossing the perimeter. ?inally! video motion detection as described in the previous

chapter is used to sense intruders. 'n high security sites! these devices are often used

in combination to minimise false alarms while ma&imising detection. n such sites!

regular perimeter patrols give the highest level of security available.

ore recently! the control of environmental and other systems around a site has been

centralised into systems using personal computers. These #uilding anagement

Systems (#S) control heating! lighting and air conditioning systems while also

providing alarms on the failure of heating boilers! e&cessive sump water levels! etc.

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The display of all these individual systems in front of an operator can be very

confusing! re"uiring a high level of training for the staff to operate the systems

individually. The level of wor for the system operator when there are multiple alarms

can also be e&cessive! as several different monitors and control panels must be used. A

better solution is to integrate these different systems in to a central display station!

such as a siteplan graphics system described in Chapter 8;. This central point then

gives the operator a single screen on which to observe and acnowledge any event in

the system using a computer mouse or touch screen the CCTV may be controlled at

the same screen.

The purpose of this chapter is to describe the ways in which these other systems may

be interfaced with the CCTV system to assemble an integrated security management

system.

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19. SUVE$IN# FO CCTV

ntrod!ction

This and the ne&t two chapters can be interpreted from two points of view. ?irst! the

installing company when designing a system. Second! with regard to the potential

customer what to e&pect from a well-presented proposal.

So far this boo has defined all the elements of a CCTV system and provided

guidelines on their operation and limitations. So now comes the time to visit a site and

design a system. This chapter cannot give detailed instruction on how to do this! ust

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as a boo on mechanical engineering cannot show a person how to design a bridge.

1owever! it does illustrate a structured approach to producing a system design that

will ensure a satisfied customer. This chapter is intended for those situations where a

company is invited to mae a system proposal from scratch. The writing of

specifications is covered in Chapter ;8.

Obtaining the %rief

The initial meeting with the prospective customer is the most important lin in the

chain to providing a final acceptable solution. 't is essential at this stage to find out

e&actly what the user is e&pecting to achieve. 't is also useful at this preliminary

meeting to e&plain the relationship between general surveillance and identification!

which is that clear identification is a trade off against the width of the area in the

scene. To start! try to obtain a definition of the fundamental obective of the system.

This could be along the lines of the following e&amples.

8. To obtain clear identification of every person passing down the corridor to the

wages office.

;. To view the general car paring areas and alert security guards if there are

persons acting suspiciously.

<. To identify the numberplate of every vehicle passing the inward barrier.

=. To cover the entire perimeter of the site and be alerted automatically in the

event of an intruder.

@. To act as confirmation of an alarm created by an intruder detection system.

>. To provide general views of the site and identification of all persons at front

and rear entrances.

1aving established the prime need of the system! use something lie the following

checlist to establish the basic re"uirements and environment. The checlists given in

this chapter are intended as a guide only. 4ach company should create their own

according to the general nature of its business.

Re/(irement N)tes

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nly a simple deterrent.

A general view of what is happening in specific areas.

A detailed view of what is happening in specific areas.

7aytime only use.

:ighttime only use.

7ay and night use.

The system is for use indoors only.

The system is for outdoor use only.

The system is for both indoor and outdoor use.

's the system to be colour! monochrome! or a mi&ture

To be integrated with other systems%ill full control of the system be on the site

's remote monitoring re"uired! i.e. central station

's continuous recording of all areas necessary

Automatic activation of aspects of the system is re"uired in the event

of an alarm.

(VC2 switched to real time! a camera sent to pre-set positions! etc.)

Ade"uate lighting is available.

Supplementary lighting is to be provided.

ounting locations are available for all cameras.

ounting locations are not available for all cameras.

%ill the system be monitored continuously

Table ;F.8 Checlist for System #rief

The list can be e&tended considerably but the intention is to obtain a general

impression of the brief. 't is not needed to answer specific "uestions at this stage.

Site 4al1abo!t

The ne&t phase is to have an informal wal around the site with the customer to

become familiarised with the topography. This also enables the names of locations

and areas to be learned. The site in this meaning could be a whole estate! a warehouse

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or a retail store! etc. This initial wal around the site will be invaluable in leading up

to the more detailed survey to be carried out.

S!rveying the Site

ost customers will provide a drawing of the site. 'f not! then a second walabout

will be necessary to mae a drawing with ey dimensions on it. The main areas of

interest will now be nown! therefore the amount of detail drawn can reflect this.

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20. SPECIF$IN# CCTV S$STEMS

ntrod!ction

There are three main types of specification for CCTV systems.

8. The proposal presented to a potential customer based on a companyEs

interpretation of preliminary visits and discussions.

;. A specification prepared by a customer in which the operating principles and

re"uirements of a system are outlined and the final design left to the

installation Company.

<. A specification prepared by a customer in which the position and performance

of every component in a system are clearly defined and specified technically.

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There is actually a fourth type of specification. This is where the customer produces a

combination of ; and < but with only a laymanEs nowledge of CCTV. This is Da little

nowledge is dangerousE type of specification.

The first part of this chapter is intended to provide guidance for the first two types of

proposal. This is followed by guidance for end users

The si/e and thicness of a proposal and specification are not necessarily proportional

to its usefulness. 'n addition! the structure of the proposal should be carefully thought

out to inform the recipient. The intention should be to provide a reasoned and

progressive argument for the system being proposed. any customers will only have

a passing nowledge of CCTV. Therefore! avoid the use of trade argon in anythingother than technical specifications where it is necessary.

ost companies will have their own preferred layout for proposals. The following

notes show a structured approach that can be adusted to fit in with any corporate

presentation.

Contract!al Considerations

The proposal will form the basis of a binding contract between the installing company

and the purchaser. 't can be the companyEs defence or downfall if there is a dispute.

%ith the best will in the world disputes will happen. 'n the case of CCTV it is

invariably the "uality of picture or scenes in view that cause the greatest problems. 't

is e"ually important to describe the drawbacs as well as the advantages of the

system. This may come across as negative thining to the salesperson but it can be

turned into a positive advantage. Statements of fact can increase the credibility of a

company and impress the customer with their ethics. This is especially the case when

the competitors have failed to point out the drawbacs.

A common comment from disappointed customers is that! G' employed your Company

as an e&pert! too your advice and now the system does not do what ' e&pected.H This

is often followed by refusal to pay the invoice. There have been many cases where

this is a smoe screen because they now donEt have the money or are simply being

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fraudulent. ?re"uently the complaint is aggravated because it is a very subective

udgement. Such comments as D' canEt read the number plates and see the whole

width of the >F-metre entrance.E D' canEt see people directly below the camera.E The

chapter on lenses made the point that many customers e&pect to see through a camera

lens what they see with their own eyes. Therefore! it is important to have laid out

e&actly what the system will and will not do. The following headings illustrate a

structured layout for a proposal.

Contents of Proposal

The proposal is the main selling document that will be presented to the customer. 't is

an opportunity to present the company as competent and professional. #esides

providing legal protection! it can persuade the customer to accept the proposed system

as the best suited to their needs. This is the document that remains after the

salesperson has left and is maybe forgotten. Another thought is that many other people

will read the document than those that met the salesperson. Therefore! it should be

easy to read and set out logically.

any companies now use word processors with a series of standard paragraphs to

construct a presentation. This obviously saves much time and can improve the

appearance of a document. 1owever! it can also give the appearance of being

produced by a machine and not a person. 't is possible to devise a word-processed

document that is personalised to each customer and his or her particular needs. ?or

instance! many companies have a standard paragraph describing a pan! tilt! /oom

camera mounted on a wall bracet with a 8F08 /oom lens! etc. This can often be about

seven or more lines of description within which may be the location and field of view.

'n a system with si&teen cameras! this paragraph may be repeated si&teen times with

ust minor changes for each location. This could tae up about five or si& pages of

repetitive information and be very difficult to comprehend. 't may loo impressive in

volume but not in communication. 'n these and similar cases the camera locations and

fields of view could be listed as one part of the proposal! followed by a separate

detailed description of the e"uipment proposed. This would be much easier to readand comprehend.

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There should be three main components in a proposal.

8. The written proposal and specification.

;. A site drawing showing camera locations and fields of view! the latter being

described in more detail within the specification.

<. A schematic diagram of the system.

Terms of Reference

This will contain a summary of the invitation to tender and any documentation and

drawings provided by the customer.

Site Visits

7etails of any site visits made and the degree of information available. Also! state

whether further visits will be necessary to finalise site details in the event of a contract

being placed. A "ualification is especially important here if a tender document

includes drawings and a description but site visits are not permitted.

S!mmary of %rief

This introductory section should describe the brief agreed between the installing

company and the customer. This will restate the overall obective for the system and

any "ualifications to it. The statements could be taen from the checlist suggested in

Chapter ;F. The purpose of this section is to ensure that both parties understand the

reasons for the specification that follows.

There will be instances where the brief has been provided by the customer without

prior discussion. 't is still important to restate it! as the basis for further comments that

will be made in the proposal.

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nterpretation of %rief

There will be occasions when further considerations will have become nown during

design of the system. These could be limitations to desired fields of view or an e&tra

camera needed! etc. These should be noted as an e&tension or restriction of the

original brief. 'f comments are omitted then the customer can assume that the

proposal meets the brief in full. A maor trap for the unwary is a document that

contains a re"uirement that the system will provide video recordings suitable for

evidential use. 'n these cases! it should be perfectly acceptable to include a

"ualification along the following lines.

/se of Video Recordings for "vidential P!rposes

't is not possible to state conclusively that all video recordings will be suitable for

evidential purposes. 't depends upon many factors! mainly the distance the suspect is

from the camera and the focal length of the lens. 9ighting! "uality of the camera!

"uality of video tape and several other factors all contribute to whether a recording is

suitable for evidence. There is also a difference between using a recording for

identification and for evidence. The rules of thumb for using video recordings are as

follows. (a) To see that it is a DpersonE rather than an animal or other obect re"uires

that the subect should be at least 8FL of the height of the screen view. This only

infers that it is a person but with no chance of identification. (b) There is a possibility

of a subect being identified if they fill @FL of the screen and are familiar to the

viewer. (c) To achieve positive identification of an unnown person they need to have

their head and shoulders fill the screen.

%ith the lenses fitted to the proposed system! the person will need to be within thirty

to fifty metres to see that it is a person depending on the lens fitted. They will need to

be within about ten to twenty metres to stand a chance of identification. Therefore the

cameras are generally positioned so that a person is moving towards them and at some

point should be of sufficient si/e on the screen to be of value.

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&escription of System

This should contain a summary of the complete system in plain 4nglish. There is no

need at this stage for any technical specification. 't should be as brief as possible!

simply an outline of the main features. An e&ample could be as follows. The system

will consist of eight e&ternal monochrome cameras. ?ive will be fully functional pan!

tilt! /oom. The others will be static units showing a fi&ed field of view. The cameras

will be connected bac to a central control unit in the gatehouse. The main control

will be a multiple&ing unit that also contains the control of the pan! tilt! and /oom

functions. The multiple&er provides the facility to almost simultaneously record all

the cameras in the system. There will be two monochrome monitors! one 8H and one

8;H.

This type of description is all that is necessary at this stage. 't simply introduces the

rest of the more detailed specifications. 'n the case of a larger! more comple& system!

it may be necessary to provide sub headings to mae a more logical description such

as.

&escription of System

- Site system.

- ain controls at site 8.

- Slave controls at site ;.

- icrowave lins.

&esign Considerations

There can be several different approaches to the final design of a system! with

different companies putting forward their own ideas. 't is fre"uently useful to provide

an e&planation outlining the reasoning behind the solution proposed. This section will

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put the proposed solution into perspective with other possible competing systems. 't

also helps to ustify the proposal compared to other systems that may be a lot less

e&pensive but do not meet the critical obectives. ne e&ample would be where the

proposed system includes cable e"ualising amplifiers because there are large

variations in cable runs. :ot all companies would consider this factor to be important!

and conse"uently submit a lower price. 4&plaining the reasons for such features can

increase confidence in the proposal and cast doubt on competing submissions.

't is also an opportunity to sell the advantages of certain maes of e"uipment where

these are important to the final performance. ?or instance! certain maes of camera or

video motion detector may include features that are not in other maes.

Sched!le of Cameras

The essential information in this section is the location and field of view for each

camera. 't may also include details of lighting conditions if e&isting lighting is to be

used. As noted previously it is preferred not to clutter this information with technical

detail or argon. 't is still part of describing the system to the customer in terms that

everybody will understand. The information would be taen from the schedule of

camera locations prepared during the site survey or produced by the customer. A

typical specification may be as follows.

CA42A :. 8 Type A

9ocation0 Corner bracet ;.@ m high on corner of building <.

Scene to view0 ; metres either side of entrance DAE.

Cable distance to control0 @m

7istance to view0 <Fm

%idth to view0 8@m

9ens focal length0 8;.@mm

9ight levels! below camera .< lu&

+ mid distance 8 lu&

+ furthest distance @. lu&

1ousing0 %eatherproof with heater Type of camera0 ?i&ed

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Any other relevant information should be listed to ensure that there is no room for

doubt as to e&actly what is being supplied. The details of light levels would be

appropriate if e&isting lighting were to be used in which case the proposal may

specify that the customer provides light to a certain average level. 'f infrared lighting

were to be used then this information would not be re"uired.

'f the system includes several types of camera! it is better to simply state the type with

a separate list of specifications for each type.

"6!ipment Specifications

The degree of specification will vary between proposals according to the type of

customer. The descriptions of e"uipment should be specific and informative. Avoid

phrases such as Dhigh performance! low light camera.E 't is argon and meaningless in

defining a camera. %hether to state the mae of each item is a matter of individual

preference. There are advantages where the manufacturer is a household name and

inspires confidence. n the other hand! with the rapid development in technology it

may be considered better to state the specification and select the most appropriate and

competitive mae when the order is placed. Some e&amples of typical specifications

follow.

21. TESTIN# AND COMMISSIONIN# S$STEMS

ntrod!ction

't is assumed that an installation has been completed according to the specification

and the relevant regulations. 't is also assumed that pre-assembly of all the systemEs

components will have been carried out according to the relevant manufacturersE

instructions. The time has arrived to test! commission! and hand over the system to the

customer. There are four main aspects to this final phase.

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Testing individual components to ensure that they operate to the design

specifications.

Commissioning all the components to function as an integrated system.

7emonstrating the system and its operation to the customer.

Training operators in the use of the system.

Testing Components

Although most components should have been checed and! if necessary! pre-

assembled before dispatch to site! the final setting up can only be carried out during

installation. Although the degree of setting up will vary according to the si/e and

comple&ity of the system! there will be certain procedures that will be common to

most systems. The following is a very brief checlist of some ey aspects that need

attention.

Cameras and $enses

Chec that the correct lens is fitted in line with the specification. Set up the lens focus

and bac focus of the camera. 'f automatic iris lenses are fitted! adust the

pea,average and level potentiometers. Chec that the field of view is as re"uired.

This will usually be adusted using a hand held test monitor. There is also available a

hand held focus aduster. 'f the camera has to cope with a wide range of light

conditions! fit a neutral density filter to set the focus at the ma&imum lens aperture.

'f a /oom lens is fitted! chec that the scene remains in focus throughout the /oom

range. 'f the focus changes! it may be necessary to rechec the camera bac focus.

Transmission

Chec every video cable for continuity and shorts to earth. A common problem is

DwhisersE of the braiding on a coa&ial cable touching the core conductor. 'f twisted

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pair transmission or video line correctors are fitted then the only correct way to set up

the system is using a pulse bar generator.

Chec through every video line to ensure that all terminations are set correctly.

&itc!ers

Chec the dwell time and se"uencing of standard video switchers. 'n the case of

matri& switchers set up the dwell times and se"uences for each monitor. 'f there is a

master,slave situation! ensure that the units are correctly located with the master

control at the main control location. Again! chec for correct terminations.

Telemetry

Chec that all functions are operating correctly and that end stops are set as re"uired.

ae sure that the pan right and tilt down controls correspond to the right direction of

movement. 'f pre-set positions are incorporated! set them up according to the

manufacturersE instructions and to the specified fields of view.

M!ltiple#ers

Set the time! date and camera titles. There will almost certainly be options to set up

the various multiscreen displays. 't is always necessary to program the multiple&er

according to the video recorder in use. ost multiple&ers now have an on screen list

of current VC2s available! in which case selection is straightforward. 'f the VC2

installed is not on this list then it will be necessary to chec with the multiple&er

manufacturer to establish the correct settings.

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Video Recorders

Some systems are supplied with separate tapes for each day of the wee or month.

4nsure that all the tapes and bo&es are mared accordingly.

All time lapse video recorders can display the time and date on the screen. 'f the

recorder is the only system component that provides this information then set it to

display. 'f there is a multiple&er or switcher that generates the information then set the

recorder not to display and use the other component for this function.

Video Motion &etection

All video motion detection systems re"uire a great deal of time and care in setting up

if they are to function efficiently and not generate false alarms. 'n the case of e&ternal

systems! it will be essential to carry out the main programming at night under the

worst lighting conditions. 'f the system is installed in the summer then it will always

be advisable to return in the winter to finalise the settings.

*ree Space Transmission

All types of free space transmission systems need rigid mountings with correct

bracets to allow alignment. Always use the manufacturersE alignment test

instruments to obtain the optimum signal strength. 't is never possible to assess the

signal simply by observation of the picture.

nterfacing with Other Systems

'f the CCTV system is being connected to another system it is advisable to have a

representative of the company which installed that other system visit the site and

approve the connections.

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Commissioning the System

nce all the components in an installation have been checed and set up it is then

necessary to commission the system to function as set out in the specification

documents. This really means operating the system from the controls and ensuring

that every function and view is as originally designed. There will usually need to be

some fine adustments made to cameras! lenses! and angles of view! etc. At this stage!

a record should be made of every camera and the scene in view. 't is also advisable to

comment on the detail that can be seen at various distances from the camera.

Commissioning will often necessitate operating the system through the night if

appropriate. $articular note should be made of the views and focus of cameras using

infrared illumination. There may be areas of flare or dar pocets that must be

considered. 't is not always easy to predict at the design stage what the effect of

infrared illumination will be. Therefore! during the commissioning stage

consideration should be given to reducing or increasing the power of some of the

lamps if they are not producing the e&pected results.

Operation and Maintenance Man!al

%hen the system is complete! an operating and maintenance manual must be handed

over to the customer. This should contain a copy of the agreed specification and

e"uipment schedule! and will form the basis of the commissioning procedures and

tests to be carried out. The manual should contain a copy of all manufacturersE data

and installation specifications. The aim should be to provide the customer with

sufficient information to be able to have the system maintained by any competent

company in the future. The need to produce this manual should be considered in the

price "uoted for the system in the first place. $roduced effectively! the manual will

represent a significant cost that should not be ignored.

An important aspect of commissioning the system will be to record all programmingand e"uipment set up procedures that have been carried out. These will need to be

138 | P a g e



included in the final operation and maintenance manual that will be handed over on

completion. There may be such items as the programming of multiple&ers! the

programming of alarm handling! se"uences set up on matri& switching systems! etc.

These should be fully documented in the system manual.

APPENDI& 1 ' #LOSSA$ OF CCTV TEMS

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This glossary is intended to provide a "uic reference to many terms used in closed

circuit television. ost of them are e&plained in much greater detail in the appropriate

sections.

4F1 INTER6ACE0 The precise combination of two fields of <8; 8,; lines to create a

single frame of >;@ lines. (CC'2)

AGC0 Automatic gain control- electronic circuitry to increase the video signal in low

light conditions. This usually introduces *noise* in the picture giving a grainy

appearance. Camera specifications should always be considered with AJC. off.

A6AR- ACTI%ATED %CR 0 ?rom selecting *record*! a normal V.C.2. would tae

from 8@ to ;8 seconds before it actually starts recording usable pictures. %ith this

type of recorder it can be set so that the tape is spooled up and ready to commence

recording in about one second. The signal to go into recording can be from an alarm

or any other input.

A6GORITH-0 athematics! a rule or procedure for solving a problem

ANA6OGUE &IGNA60 'n video! the representation of a camera scene by varying

voltages in the video signal! the voltage being directly proportional to the light level.

APERTURE0 The light gathering area of a lens. The iris controls the si/e of the

aperture.

AR-OUR 0 4&tra protection for a cable that improves resistance to cutting and

crushing. The most common material used is steel.

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A&PECT RATIO0 The ratio of the vertical to the hori/ontal image si/e. This is <0=.

ATTENUATION0 A term that refers to signal loss in a transmission system or light

loss through a lens system.

AUTO-ATIC IRI&0 A lens that automatically adusts to allow the correct amount of

light to fall on the imaging device. There are a tiny motor and amplifier built in which

generally receives a control signal from the camera to maintain a constant one volt

pea to pea (pp) video level. There are two manual controls on the lens to allowcompensation for varying conditions of *pea* and *average* light.

BACK ;OCU&0 A mechanical adustment in a camera that moves the imaging device

relative to the lens to compensate for different bac focal lengths of lenses. An

important adustment when a /oom lens is fitted.

BA6ANCED &IGNA60 A video signal converted to a balanced signal! usually to

enable it to be transmitted along a *twisted pair* cable. 5sed in situations where the

cabling distance is too great and which would produce unacceptable losses in a

coa&ial cable.

BAND<IDTH0 The amount of space in a given part of the spectrum needed to carry

communication signals.

BU;;ER 0 The material surrounding the fibre to protect it from physical damage

B6ANKING PERIOD0 The period of the composite video at blac level and below

when the retrace occurs! maing it invisible on the screen.

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B6ACK 6E%E60 The dar parts of a video signal corresponding to appro&imately

F.< volts.

BI;URCATOR 0 An adapter with which a loose tube containing two optical fibres

can be split into two single fibre cables. (See loose tube)

C.-OUNT0 The standard screw mounting for ;,<+ and 8+ camera lenses. The

distance from the flange surface to the focal point is 8.@;> mm. A C-mount lens can

be used on a camera with a CS- mount by adding an adapter ring to reduce this

distance to 8;.@ mm. (See CS-mount )

CAB6E EUA6I&ER 0 An amplifier to increase a video signal to the optimum value.

This is usually to compensate for cable losses.

CCD0 Charge coupled device! a flat thin wafer that is light sensitive and forms the

imaging device of most modern cameras. Si/e is measured diagonally and can be

8,<+!8,;+ or ;,<+. There are two types! frame transfer and interline transfer.

CCIR 0 The 4uropean >;@ line standard for the video signal.

CHRO-A BUR&T0 The reference signal included in the video signal after the

hori/ontal sync pulse. This enables a colour monitor to loc on to a colour composite

video signal

CHRO-INANCE0 The part of a colour video signal that carries the colour

information.

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C6ADDING0 The outermost region of an optical cable! less dense than the central

core. Acts as an optical barrier to prevent transmitted light leaing away from the

core.

CO-PO&ITE %IDEO0 The complete video signal comprising the sync and video

information. The sync pulse should be .< volts and the video signal should be . volts.

CORE0 The central region of an optical fibre through which signal carrying infrared

is transmitted. anufactured from high density silica glass.

C&.-OUNT0 A new generation of lenses designed for! 8,;+! 8,<+ ! 8,=+ and 8,B+

cameras incorporating CS-mounts. The distance from the flange surface to the focal

point is 8;.@ mm. CS-mount lenses cannot be used on cameras with C-mount

configuration. These lenses are more compact and cheaper than the C-mount

e"uivalents.

dB0 7ecibel! a logarithmic ratio between two signals.

DEPTH O; ;IE6D0 The proportion of the field of view that is in correct focus. The

depth of field in focus 74C24AS4S when0 the focal length is longer! the f number is

smaller! or the obect distance is shorter.

DE&KTOP &<ITCHER 0 A device for switching the video signal from several

cameras to one or more monitors. The cables from the cameras are connected to the

bac of the unit.

DIGITA6 &IGNA60 An analogue signal that has been converted to a digital form so

that it can be processed by a micro processor.

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EIA0 The American @;@ line standard for the video signal.

f &TOP0 This is the ratio of the focal length to the effective diameter of the lens.

(f,A). 't is not a measure of the efficiency or the transmission value of the lens. The

smaller the f number the more light is passed.

fc0 ?oot candles used in some 5SA specifications to define sensitivity. 8F fc is appro&.

8 lu&.

;IBRE OPTIC0 A very efficient method of transmitting video and telemetry signals

over very long distances using fibre optic cable. Signals can be multiple&ed and sent

along a single fibre.

;IE6D O; %IE<0 The relationship between the angle of view and the distance of

the obect from the lens.

;IE6D0 ne half of a frame consisting of <8; 8,; lines! @F fields are created every

second.

;6ANGE BACK 6ENGTH0 The distance from the bac flange of a lens to the

sensor face. This is 8.@;>mm for C mount and 8;.@mm for CS-mount lenses.

;OCA6 6ENGTH0 The distance between the secondary principal point in the lens

and the plane of the imaging device. The longer the focal length! the narrower is the

angle of view.

;RA-E &TORE0 An electronic method of capturing and storing a single frame of

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video. All slow scan transmitters include a frame store that holds the picture at the

moment of alarm! while the control is being dialled up. %hen the lin is confirmed!

the picture is transmitted.

;RA-E TRAN&;ER 0 A type of CC7 imaging device in which the entire matri& of

pi&els is read into storage before being processed by the electronics of the camera.

;RA-E0 The combination of two interlaced fields! ;@ frames are created every

second.

GA--A CORRECTION0 An electronic correction carried out in the camera

circuitry to balance the brightness seen by the camera to that of the monitor.

GEN 6OCK 0 Also called e&ternal sync. A separate coa&ial cable is run to each

camera and carries sync pulse information to ensure that all cameras are producing

fields at e&actly the same time. This eliminates picture bounce during switching and

can improve "uality and update time in multiple&ers.

GRADED INDE0 (Jraded inde& profile). A measurement shown in the form of a

diagram which illustrates how the "uality of glass used in this type of optical fibre

alters gradually. ?rom the densest at the core to the optically less dense cladding.

GROUND 6OOP TRAN&;OR-ER 0 An isolation transformer so that there is no

direct connection between input and output.

GROUND 6OOP0 An AC current that can be produced in a cable. This is usually

caused by parts of the system being fed from different electrical sources resulting in

different earth potentials at each end. The result is interference on the signal.

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HARD<IRED0 Controlling remote e"uipment by direct voltage transmitted along a

multicore cable from the main controller. This is very labour intensive to install and is

only used in simple systems with short cable runs.

HERT H*0 The number of variations or cycles per second.

I66U-INANCE0 The measurement of light in lumens per s"uare metre! the unit of

which is the lu&.

I-PEDANCE0 A measure of the total opposition to current flow in an alternating

current circuit! measured in hms.

IN;RA RED 6IGHT0 The wavelength of light produced above the visible part of the

spectrum.

IN;RA RED TRAN&-I&&ION0 A method of transmitting video and telemetry

signals across free space along an infra red beam. This opens possibilities for using

C.C.T.V. where it had been previously impossible to run cables. 7istance can be

limited and the signal can be degraded in adverse weather conditions.

INTER6INE TRAN&;ER 0 Another type of CC7 imaging device in which the rows

of charge are stepped down one at a time and processed straight away.

INTERNA6 &9NC0 The internal generation of sync pulses in a camera without

reference to e&ternal sources. This uses a crystal controlled oscillator and is needed on

non mains powered cameras.

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IP RATING0 'nde& of protection! a number combination that defines the protection

afforded from outside influences by an enclosure.

IR2 &HI;T0 The difference in the field of view in focus between daylight and infra

red light.

RE;ERENCE

!tt+F2cct".inf)rmati)n2c)2($

!tt+F2cct".inf)rmati)n2c)2($iT!eLPrinci+lesLM47LPracticeL)fLCCT%

http://www.cctv-information.co.uk/

http://www.cctv-information.co.uk/i/The_Principles_%26_Practice_of_CCTV

http://www.cctv-information.co.uk/

http://www.cctv-information.co.uk/i/The_Principles_%26_Practice_of_CCTV

closed circuit television camera installation and networking

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