formatted smoke detectors

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SMOKE DETECTION AND ALARM SYSTEMS INTRODUCTION: Fire is detected by having sensors that detect the by- products of fire, typically heat and smoke but also ultraviolet & infra-red radiation. Detection of heat has long been the only method of automatically detecting a fire. This is because it could be implemented relatively easily using mechanical detection means, and the effects of heating and heat transfer were fairly well known. However since the electronic advancements in the 1940s, smoke detection has also been available. However it was not until the last couple of decades that smoke detection has become reliable and cost effective to be used widely, yet this may not always be the most appropriate detection method. Smoke detectors are a much newer technology, having gained wide usage during the 1970's and 1980's in residential and life safety applications. As the name implies, these devices are designed to identify a fire while in its smoldering or early flame stages, replicating the human sense of smell. The most common smoke detectors are spot type units, that are placed along ceilings or high on walls in a manner 1

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Page 1: Formatted Smoke Detectors

SMOKE DETECTION AND ALARM SYSTEMS

INTRODUCTION:

Fire is detected by having sensors that detect the by-products of fire, typically heat

and smoke but also ultraviolet & infra-red radiation. Detection of heat has long been

the only method of automatically detecting a fire. This is because it could be

implemented relatively easily using mechanical detection means, and the effects of

heating and heat transfer were fairly well known. However since the electronic

advancements in the 1940s, smoke detection has also been available. However it was

not until the last couple of decades that smoke detection has become reliable and cost

effective to be used widely, yet this may not always be the most appropriate detection

method.

Smoke detectors are a much newer technology, having gained wide usage

during the 1970's and 1980's in residential and life safety applications. As the name

implies, these devices are designed to identify a fire while in its smoldering or early

flame stages, replicating the human sense of smell. The most common smoke

detectors are spot type units, that are placed along ceilings or high on walls in a

manner similar to spot thermal units. They operate on either an ionization or

photoelectric principle, with each type having advantages in different applications.

For large open spaces such as galleries and atria, a frequently used smoke detector is a

projected beam unit. This detector consists of two components, a light transmitter and

a receiver, that are mounted at some distance (up to 300 ft/100m) apart. As smoke

migrates between the two components, the transmitted light beam becomes obstructed

and the receiver is no longer able to see the full beam intensity. This is interpreted as a

smoke condition, and the alarm activation signal is transmitted to the fire alarm panel.

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Importance of smoke detectors:

Smoke detectors are one of the most important safety devices one can have

in the home. They should be installed in the hallways and in the bedrooms. Smoke

detectors provide early warning in the event of a fire, and enable emergency action in

the event of a fire. They are inexpensive, easy to install, unobtrusive, and require very

little maintenance, and no home should be without them.

Most experts agree that smoke is responsible for approximately 80 percent of the

fatalities caused by fires. This fact of life has triggered the phenomenal growth in

popularity of residential-type smoke detectors. In many communities, legislation has

been passed requiring the installation of smoke detectors in houses and apartments.

And the dramatic rise in residential smoke detector popularity is spilling over into

industry not only as life-saving devices, but also as a key part of fire protection

systems for buildings and equipment.

The National Electrical Manufacturers Association (NEMA) in its Standards

Publication SB 9 defines a smoke detector as "a device which detects visible or

invisible particles of combustion." The publication points out that the real value of

such a device lies in its ability to detect a fire even before flame and large quantities

of heat develop . All smoke detectors depend on various combinations of minute

liquid or solid particles suspended in a gaseous dispersion agent for their operation.

Particle characteristics that affect detection thresholds include diameter, shape,

internal structure, optical properties, and concentration.

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How Good Are Smoke Detectors?

The common home smoke detector cost around $10 and will detect smoke in very

small concentrations in the home. Smoke emission occurs during the early stages of a

fire, so smoke detectors in the ceilings of the home will provide plenty of early

warning in the event of fire.

The key advantage of smoke detectors is their ability to identify a fire while it

is still in its incipient. As such, they provide added opportunity for emergency

personnel to respond and control the developing fire before severe damage occurs.

They are usually the preferred detection method in life safety and high content value

applications.

Evolution of smoke from fire:

When a nice fire is going, and it has burned down to the point where a collection of

hot "glowing embers is seen." The fire is still producing a lot of heat, but it is

producing no smoke at all. If a piece of wood is tossed, or even a sheet of paper, onto

this fire, it is noticed that the new fuel produces a lot of smoke as it heats up. Then,

all of a sudden (often with a small pop), it bursts into flame and the smoke disappears.

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When a fresh piece of wood or paper is put on a hot fire, the smoke that is seen

are volatile hydrocarbons evaporating from the wood. They start vaporizing at a

temperature of about 300 degrees F (149 degrees Celsius). If the temperature gets

high enough, these compounds burst into flame. Once they start burning, there is no

smoke because the hydrocarbons are turned into carbon dioxide and water (both

invisible) when they burn.

. Coke is coal that has been heated in the absence of oxygen to drive off the

organics. The smoke that this process produces is actually very valuable .It contains

coal tar, coal gas, alcohols, formaldehyde and ammonia, among other things. And all

of these compounds can be distilled out of the smoke for use. Methanol (a form of

alcohol) referred to as "wood alcohol.” is used to be produced by distilling out of

wood.

Detector operating times - Smoke detectors

At present there are no models or calculations to predict the operation time of smoke

detectors. There are, however, a number of methods used to predict the operation of

the detector. The first method is to generate an "equivalent" thermal detector that has

an activation temperature of 10-200C above the ambient and a low RTI value. This is

then used in the thermal detector calculations as an indication of the response of the

smoke detector. This method however is only an estimation and generally considered

as a "rule of thumb" rather than an accurate measure. The other method of

determining the detector response is by using the smoke transport models.

There are two types of models available, the zone model and the field

models. The field models are considered to give a more accurate picture of what

actually happens though they aren't combined with simple detector operating time

functions and take much longer to run. Hence, generally the zone models are used

when considering detector operation. The zone model typically divides the fire

compartment into two zones, the upper layer and the lower layer. The upper layer is

the location of the smoke and gases and the detector. The zone model calculates the

volume, smoke density, temperature size and other factors for the upper layer at

discrete time intervals from the fire initiation. As the optical density of the smoke is

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calculated at various points in time the fire engineer can make an evaluation as to

when the detector will activate based on the sensitivity of the detector.

Smoke detection:

The future of performance based design lies largely with smoke detection as the

production of smoke is usually the first combustion product to be released, hence if it

can be detected then we will achieve a faster detection time and therefore longer

escape time.

The general modeling procedure was to run the zone model and work out

values for the optical smoke density at the upper layer at various points in time. When

the optical density reached the rating of the detector then one could assume that the

detector would operate. However in real life there are a number of factors why this is

an invalid scenario.

One of the main reasons is the same as for thermal detectors in that an exact

activation optical density is not know, rather a range. Smoke detectors are grouped

into 3 sensitivity groups Normal, High and Very High. Each of these groups has a

nominated sensitivity range that the detector must fall in. However the foremost

reason why a direct relation between the expected optical density of smoke produced

and the actual detector performance cannot be produced is due to the actual operation

of the detector. In general smoke detectors do not measure smoke obscuration

directly, rather some other factor related to smoke obscuration. Thus the operation of

each of the different types of smoke detectors needs to be considered to see where the

problems lie in the performance of the various types.

Different types of smoke detectors and their operation:

Not all fires are alike. Some are slow burning and smoky, some are fast burning,

producing high heat but less smoke. Each type of fire requires an appropriate

technology.

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The various types of smoke detectors are:

Photoelectric smoke detectors.

Ionization smoke detectors.

Laser technology smoke detectors.

Detectors based on air sampling technology.

Infrared beam smoke detectors.

Video smoke detectors

Photoelectric Detectors:

Photoelectric detectors are better at sensing smoky fires, such as a smoldering

fires .Occasionally, when we walk into a store and a bell will go off as we cross the

threshold. If we look, we will often notice that a photo beam detector is being used.

Near the door on one side of the store is a light (either a white light and a lens or a low-

power laser), and on the other side is a photodetector that can "see" the light.

When we cross the beam of light, we block it. The photodetector senses the lack

of light and triggers a bell. In a similar way, this same type of sensor could act as a

smoke detector. This is known Photo-optical detectors obviously use a light source to

measure smoke density but rather than measure how much the intensity of the light is

reduced due to the smoke they measure how much light is reflected by the smoke.This

is known as the light scatter principle.

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In one type of photoelectric device, smoke can block a light beam. In this case, the

reduction in light reaching a photocell sets off the alarm. In the most common type of

photoelectric unit, however, light is scattered by smoke particles onto a photocell,

initiating an alarm. In this type of detector there is a T-shaped chamber with a light-

emitting diode (LED) that shoots a beam of light across the horizontal bar of the T. A

photocell, positioned at the bottom of the vertical base of the T, generates a current

when it is exposed to light. Under smoke-free conditions, the light beam crosses the

top of the T in an uninterrupted straight line, not striking the photocell positioned at a

right angle below the beam. When smoke is present, the light is scattered by smoke

particles, and some of the light is directed down the vertical part of the T to strike the

photocell. When sufficient light hits the cell, the current triggers the alarm. The sensor

then sets off the horn in the smoke detector.

. The diagram below illustrates how the technology works. Under normal,

smoke-free conditions, the LED beam moves in a straight line, through the chamber

without striking the photo cell. When smoke enters the chamber, smoke particles

deflect some of the light rays, scattering them in all directions. Some of it reaches the

photocell. When enough light rays hit the photocell, they activate it. The activated

photocell generates a current. The current powers the alarm, and the smoke alarm has

done its job. 

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Photoelectric Smoke Alarm Technology

smoke free chamber 

light beam travels straight through 

smoke particles in chamber

deflect some light rays     

Light 

emitting 

diode 

  

activated

photocell

powers alarm

no light reaches photoelectric

cell

  deflected light rays 

  activate photocell

        

But there are two problems here: 1) It's a pretty big smoke detector, and 2) it is not

very sensitive. The main problem with this is that the detector is only generally

sensitive to particle sizes around the size of the wavelength of the light used. Thus it

would be possible for smoke, with an optical density greater than the rated activation

sensitivity, that consisted of small unreflective particles to be present and not cause

activation of the detector. Photoelectric detectors look for the presence of visible by-

products of combustion in the detection chamber. When a sufficient density of visible

combustibles fill the detection chamber, the detector sounds an alarm condition.

Ionization smoke detectors:

Ionising smoke detectors are approved by the Swedish Institute of Radiation

Protection and contain radioactive sources. The advantage of ionization detector is

that the smoke can be invisible to the human eye, while remaining very much visible

to the ionization detector.

In the conventional devices , the material is nearly destroyed before

alarm comes as they are triggered only when sufficient smoke or heat is evolved .On

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the other hand , the Ionization detectors sense these particles at the incipient stage by

monitoring the electrical change which occurs when the particles reach the charged

space in the detector.

Ionization technology is faster at reacting to fast flaming fires that give off

little smoke. . Ionization smoke detectors feature a harmless radioactive source within

a dual detection chamber. They operate by sensing for a change in the electrical

conductivity across the detection chamber. . This type of smoke detector is more

common because it is inexpensive and better at detecting the smaller amounts of

smoke produced by flaming fires.

Ionization chamber is very simple. It consists of two plates with a voltage

across them, along with a radioactive source of ionizing radiation , a small amount

(perhaps 1/5000th of a gram) of americium-241 to detect the smoke. The radioactive

element americium has a half-life of 432 years, and is a good source of alpha

particles. . Typical detector contains 0.9 microcurie of americium-241. A curie is a

unit of measure for nuclear material. The amount of radiation in a smoke detector is

extremely small. It is also predominantly alpha radiation. Alpha radiation cannot

penetrate a sheet of paper, and it is blocked by several centimeters of air. The

americium in the smoke detector could only pose a danger if you were to inhale it.

In this chamber, the americium is embedded in a gold foil matrix within an

ionization chamber. The matrix is made by rolling gold and americium oxide gets

together to form a foil approximately one micrometer thick. This thin gold-americium

foil is then sandwiched between a thicker (~0.25 millimeter) silver backing and a 2

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micron thick palladium laminate. This is thick enough to completely retain the

radioactive material, but thin enough to allow the alpha particles to pass.

Americium: The vital ingredient of household smoke detectors is a very small

quantity (<35 kBq) of americium-241 (Am-241). This element was discovered in

1945 during the Manhattan Project in USA. The first sample of americium was

produced by bombarding plutonium with neutrons in a nuclear reactor at the

University of Chicago.

Americium is a silvery metal, which tarnishes slowly in air and is soluble in

acid. Its atomic number is 95. Its most stable isotope, Am-243, has a half-life of over

7500 years, although Am-241, with a half-life of 432 years, was the first isotope to be

isolated.Americium oxide, AmO2, was first offered for sale by the US Atomic Energy

Commission in 1962 and the price of US$ 1500 per gram has remained virtually

unchanged since. One gram of americium oxide provides enough active material for

more than 5000 household smoke detectors.

Americium (in combination with beryllium) is also used as a neutron source in

non-destructive testing of machinery and equipment, and as a thickness gauge in the

glass industry. However, it’s most common application is as an ionisation source in

smoke detectors, and most of the several kilograms of americium made each year is

used in this way.

Formation of Americium

Plutonium-241, which is about 12% of the one percent content of plutonium in typical

spent fuel from a power reactor, has a half life of only 14 years, decaying to Am-241

through emission of beta particles. Am-241 has a half life of 432 years, emitting alpha

particles (see above) to become neptunium-237. The plutonium 241 is formed in any

nuclear reactor by neutron capture ultimately from uranium (actually U-238), such as

supplied on the world market for electricity generation. The detailed steps are:

U-238 + neutron => U-239,

U-239 by beta decay => Np-239,

Np-239 by beta decay =>Pu-239,

Pu-239 + neutron => Pu-240,

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Pu-240 + neutron => Pu-241.

This will decay (emitting a beta particle) both in the reactor and subsequently.

Principle of operation:

The alpha particles generated by the americium have the following property: They

ionize the oxygen and nitrogen atoms of the air in the chamber. To "ionize" means to

"knock an electron off of." When you knock an electron off of an atom, you end up

with a free electron (with a negative charge) and an atom missing one electron (with a

positive charge).. The positive atoms flow toward the negative plate, as the negative

electrons flow toward the positive plate. The movement of the electrons registers as a

small but steady flow of current. When smoke enters the ionization chamber, the

current is disrupted as the smoke particles attach to the charged ions and restore them

to a neutral electrical state. This reduces the flow of electricity between the two plates

in the ionization chamber hat these electrons and ions moving toward the plates

represent. The electronics in the smoke detector sense the small amount of electrical

current. . When the electric current drops below a certain threshold, the alarm is

triggered.

.

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Chemical reactions in the Ionisation smoke detector:

It is more a physical reaction than a chemical reaction. the americium in the smoke

detector is high speed alpha particles (helium nuclei).the particles hit molecules in air

and knock off electron.

o2+he(+2)o2(+1)+e(-1)+he(+2).

Working:

The working of the fire alert ionization chamber detector is shown in the

fig:

FIG (1)

The detector is basically a simple series resistance , capacitance (RC)

Circuit . The charging current to charge the capacitor is supplied by the ionised

air in the sample chamber , which constitutes the resistance R. The charge carriers

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are a mixture of electrons and positive ions produced by high velocity alpha

particles.The positive ions enter the sample chamber .

The circuit works in a cycle with the voltage(E+) on the

capacitor(C) being an exponential function of time . Under normal conditions the

capacitor (C) will be allowed to build up a charge ( CE) determined by the integration

timer (T).If at the integration cycle time the capacitor C has received adequate

charge to trigger the charge detector (Q) it will set for (RC+2) seconds.

When this occurs both timers (T) and (T+2) will repeat the above cycle. If the

positive ions of the products of combustion are introduced into the sample

chamber , the resistance of the chamber is increased and the capacitance (C) does not

fully charge in the time constant established by the integration timer(T). Under this

condition the charge detector (Q) will not reset both timers .If the alarm timer (T+2)

is not reset it will complete its cycle and cause the alarm relay to “lock in” indicating

the alarm condition.

The circuit is infinitely adjustable for cycling timer by the presetter

and the sensitivity variable resistors .The maximum allowable cycle time represents

‘minimum sensitivity’and the minimum allowable cycle time represents the

maximum sensitivity .When set for maximum sensitivity, it exhibits extreme

sensitivity with the ability to detect even the electrical short circuit or overload

conditions .When set for minimum sensitivity it provides an alarm with test fires with

an established sensitivity to monitor 360 sq .m. of area .The detector is stable at any

sensitivity and is not adversely affected by air velocity ,humidity or temperature from

-10C to 65C.

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This principle of working of this detector could be better understood by the actual

relay circuitry shown in the fig (2):

In the fig , TDR1 is a time delay relay which closes a normally open contact 1

TDR1 aft r some time delay . This time delay is set such that after this time, under

normal atmospheric conditions the charge built up across the capacitor C will be

sufficient to energise the relay Q , which otherwise will not pick up before this

voltage . 1Q&2Q are the normally closed contacts of the relay Q and these contacts

open out when the relay Q is energized . TDR2 is another timer which I set at time

equal to 2seconds more than the time for which TDR1 is set and ITDR2 is its

normally open contact which initiates the alarm . Under normal atmospheric

conditions i.e when there is no fire , the charge built up across capacitor after time T

is equal to E which can energise relay Q .Also after time T i.e , for which relay

TDR1has been set the contact 1 TDR1 makes and the relay Q is thus energized. Due

to its energisation the timers TDR1&TDR2 cease to get supply and are reset .

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Incase fire is there , then the resistance (R)of the circuit is increased and the

exponential curve is modified as shown in the fig 3.

Under this condition , after time T , the contact ITDR1 makes but relay Q can’t be

energized because voltage across the capacitor is only E’’ which is less than E’ and

hence not sufficient to energise relay Q . As a result the timer TDR1 &TDR2 are not

reset and after time (T+2)seconds the contact ITDR2 makes and initiates the alarm.

Special features:

1> This device operates at 24 V DC(full wave rectified )thus giving a safe and simple

operation and consumes only 3 to 4 watts.

2> It is capable of operating in fast moving air and is impervious to moisture and

corrosion .

3> A lamp is incorporated in the unit to give visual indication when detector operates

and a separate lamp can be provided to give remote indication also.

4> No expensive equipment is required to provide stand by supply in the event of

mains failure .

5> Its operation is not effected by transients in supply or normal voltage fluctuations.

6> I t is capable of operating at sub zero temperatures and elevated temperatures with

no change in operations.

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Inside a ionisation Smoke Detector

. Here is the smoke detector:

When we take off the cover we find that a smoke detector is pretty simple. This one

consists of a printed circuit board ,an ionization chamber (the silver cylinder toward the top

right in the following picture) and an electronic horn (the brass cylinder toward the bottom

right in the following picture):

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Here is a close-up of the board:

and the underside of the board:

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Amount of radiation in Ionisation smoke detectors:

The radiation source in an ionization chamber detector is a very small disc, about 3 to

5 millimeters in diameter, weighing about 0.5 gram. It is a composite of americium-

241 in a gold matrix. The average activity in a smoke detector source is about one

microcurie, 1 millionth of a curie.

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Americium emits alpha particles and low energy gamma rays. It has a half-life

of about 432 years. The long half-life means that americium decays very slowly,

emitting very little radiation. At the end of the 10 year useful life of the smoke

detector, it retains essentially all its original activity.

How much radiation exposure will be got from a smoke detector?

As long as the radiation source stays in the detector, exposures would be negligible

(less than about 1/100 of a million per year), since alpha particles cannot travel very

far or penetrate even a single sheet of paper, and the gamma rays emitted by

americium are relatively weak.

HIGH SENSITIVITY SMOKE DETECTOR USING

LASER TECHNOLOGY

Features:

Unique smoke particle counting technology

Fast detection of incipient fire

Smoke detection capability from 0.005% to 0.4% obscuration per meter

Calibrated by using smoke-like particulate

Immune to contamination and dust levels reducing false alarms

Minimal periodic maintenance

Low susceptibility to environmental conditions

Senses smoke even in high air flow design

No filter required

No re-calibration required

Incorporates military proven state-of-the-art laser technology

Established laser design ensures long-term stability and accuracy

Long life under-run key electronic components

Can be fitted into existing fire detection and alarm system

Description:

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The HART high sensitivity smoke detector assembly consists of a metal fan box

and the HART HSSD detection sensor.

The fan box is a robust airtight enclosure which houses a high efficiency

centrifugal fan, superior to an axial fan, producing a greater static pressure necessary

to draw air into the detector.

The air passes without filtration straight through the detection chamber.

This design ensures elimination of filter maintenance (with the inherent possibility

of filtration of smoke particulate) and no flow restriction to the incoming air.

The detector's unique patented optical system focuses a 100 micron laser beam

through the detector chamber.

The detection device detects the presence of individual particles of smoke as they

traverse the laser beam in the moving air stream.

Smoke concentration is determined by counting these discrete events.

This particle count is converted to an analogue signal whose level is exactly

proportional to the smoke concentration, the output of which is available for

transmission to the control panel.

Changes in flow do not affect the measured value of smoke concentration.

The HART HSSD is essentially a particle counter set up to discriminate between

smoke and other potentially confusing particulate

It requires no filter and is immune to the normal levels of airborne dust and to

contamination of the chamber walls.

In large other very early smoke detectors, particles such as dust give "false" alarm

signals; but the HART detector incorporates an adjustable particle size discriminator

(in addition to the particle counting circuitry) which ensures that the HART HSSD

provides output only to smoke itself.

Its unrestricted airflow design ensures that the sensor truly sees the room air

environment. The laser deployed in the HART HSSD is the same type as that used in

CD players.

Refined by Japanese engineering, this type of laser provides a long-term stable

output.

Any changes in laser intensity due to temperature, component ageing or dirt build-

up are automatically compensated for electronically - in the detector itself without

reliance on control software.

Circuits supervise the operation of critical components in the system.

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Failure of, or an out of tolerance situation in the illuminating or receiving optics,

will result in a detector FAULT signal being transmitted to the control panel.

Air flow is monitored with a special temperature sensor, cooled by air passing

through the detection chamber.

An analogue signal proportional to flow is made available to the control panel so

that it can initiate a fault condition, should the air flow vary or drop during normal

operation.

The HART detector is available in different versions each with a sensitivity to suit

different applications and area of protected space.

HART detectors are assembled into standard packages for use in a wide range of

applications:

HART 100 - the most sensitive detector available from 0.05% to 0.2% obscuration

per meter at full scale, it can be supplied in the approved HART fan box, UniLaser

100 & 1000, LocaLaser, Smoke Seeker and EExd versions. HART 200 - has a

sensitivity of nominally 0.4% obscuration per meter and is available in the basic

HART fan box and UniLaser 200 & 2000 versions.

The HART packaged options include Display Control Card (DCC) and HART

detector in fan box (available in HART 100 and HART200 versions).

Controls packaged as a single or up to 4 zone unit mounted separate to HART

detector enclosed with integral fan in fan box.

UniLaser 100 and UniLaser 200 - single station HSSD

Controls, detector and fan in a single enclosure.

Functionally identical to the DCC and HART detector.

UniLaser 1000 and UniLaser 2000 - single station HSSD

Controls, detector, fan, and power supply with space for up to 24 hours of stand-

by in a single enclosure.

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Functionally identical to the DCC and HART detector with the added feature of

an integral power supply SMART HART HSSD in fan box

Direct communication to any analogue addressable panel fitted with suitable

software and operating on the Apollo series 90 protocol.

LocaLaser - multi-zone HSSD

Based on the UniLaser concept but with the ability to identify smoke in up to 4

separate zoned areas of sampling.

Smoke Seeker - multi-point HSSD

Specialized smoke sampling to identify the location of smoke from up to 8

separate points of sampling.

Ideal fo EExd

Fully certified HSSD unit for applications of Zone 1 areas of hazardous

protection.

Used in combination with a Display Control Card, or alternatively as a SMART

version.

Ideal for cabinet detection.

Laser Particle Counting Technology :

Laser Particle Counting technology provides the leap forward. Instead of illuminating

the whole sampling chamber, lasers afford the ability to illuminate just a discrete

volume element in the center of the sampling chamber.In this way, the detector

becomes essentially immune to any contamination of the chamber walls.

More important is the fact that HART High Sensitivity Smoke Detectors are set up as

single particle counters.

HSSD as Single Particle Counters:

As the smoke particulate passes into the sampling element, the sensor electronically

counts each particle. Particle counting HSSD devices are thus much more sensitive to

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the prevailing concentration of small particulate (the tell tale sign of early

combustion) than are conventional HSSD devices. Although larger particulate such as

dust does not significantly affect the signal recorded (number of particles) from either

a background or a prevailing smoke environment, the HART laser HSSD goes one

step further. Most particulate with a diameter less than 10 micrometers is

electronically recognized and thus not added to the smoke count register.

AIR SAMPLING SMOKE DETECTORS

Aspirating Smoke Detectors

Introduction :

Aspirating smoke detection is a system that uses an aspirating fan to draw air from the

protected area via a network of sampling pipes and sampling holes.The sampled air is

then passed through a high sensitivity precision detector that analyses the air and

generates warning signals when appropriate. This system has a number of benefits,

particularly in the areas of performance, installation cost and routine maintenance.

The two main types of system are:

Primary Sampling System:

The system is designed to work in conjunction with any air handling systems and will

not provide optimum performance when these are inoperative. The major advantage is

the detection of cool smoke from a minor problem that does not rise to the ceiling,

which would be the ‘conventional’ location.

Secondary sampling system: : The system is designed with sampling holes in the

same positions as normal point detectors to an appropriate standard.These sampling

pipes may be designed and installed to achieve one of three levels of sensitivity:

_ Normal Sensitivity: the same sensitivity as normal point detectors typically at 3% -

5% obscuration per metre.

_ Enhanced Sensitivity:responding to smoke at concentrations of between 2%

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and 0.8% obscuration per metre.

_ High Sensitivity: responding to smoke at concentrations of less than 0.8%

obscuration per metre.

It is important to note that the detector sensitivity is shared over the network of

sampling points associated with it. In other words, if a system having a detector

registering a ‘Fire’ signal when the smoke density within it reached 0.05%

obscuration per metre was connected to a pipe network with 20 sampling holes the

mean system sensitivity at each hole would be 1.0% (0.05% x 20). This sensitivity is

calculated on the basis smoke only enters one of the twenty holes. If the same density

of smoke entered two holes the mean sensitivity would double. Normally, smoke will

enter from the majority of sampling holes, in which case system sensitivity can be

very high indeed.

Types of Detectors:

There are currently three types of technology used in commercially available

aspirating smoke detectors:

Light Scatter: A stream of sampled air is continually passed through a detection

chamber in which a high-energy light source is pulsed. This light would be scattered

by any smoke particles in the sample and the quantity of scattered light is analysed by

a solid state light receiver. The quantity of scattered light is proportional to the level

of smoke pollution. Light scatter systems are sensitive to smouldering fires and

particles given off by overloaded electrical cables and are therefore particularly useful

where early warning is required. They can be vulnerable to dust however, which is

why most detectors incorporate sophisticated filters and/or electronic dust rejection.

Cloud Chamber: A stream of sampled air is continually passed through a detection

chamber that contains water vapour.Any very small particles cause the vapour to

condense around them to form larger droplets of equal size. The number of these

droplets is regularly measured optically using a pulsed LED. Because cloud chambers

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consume water they require regular maintenance. Cloud chamber detectors are

resistant to dust.

In comparative field tests, cloud chamber detectors have shown very good

response in detecting the particles released by flaming fires, but poor response in

detecting the particles common to smouldering fires and are therefore of limited use

for early warning.

Particle Counting: A stream of sampled air is continually drawn through a focused

laser beam and light scattered from each particle is measured. This provides an output

relative to the number of particles that have traversed the laser beam. Particle

counting systems are sensitive to smouldering fires and overloaded cables but need to

have their air flow vigorously regulated as their output is proportional to the flow rate.

Particle counting systems are generally resistant to dust but fibres seen ‘end on’ or

large volumes of dust have been known to cause unwanted alarms.

Signal processing:

How signals are processed is fundamental to the reliability of an aspirating detection

system.Provision should be made to accommodate changes resulting from a drift in

detector calibration, contamination of filters or changing environmental conditions

within the protected area, thus ensuring a consistent level of protection.Early

aspirating detection systems were of fixed sensitivity where the detector was

calibrated to a known value and the alarm thresholds fixed at pre-determined points

depending on the site conditions measured during commissioning. These systems

were unable to accommodate fluctuation in site conditions and this rapidly led to a

perception that high sensitivity automatically meant a high incidence of unwanted

(false) alarms. All fixed sensitivity detectors require annual recalibrating in addition

to normal maintenance test procedures.To overcome this problem, a modern

aspirating system uses Artificial Intelligence (AI) to maintain a known probability of

alarm by varying the sensitivity of the detector to match variations in site conditions.

This type of system also automatically compensates for component drift or detector

contamination, thus ensuring optimum performance is always achieved.

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General Design Aspirating smoke detectors are often used where early

warning is required and higher than normal sensitivity is needed. They are also

suitable for many other applications where there are problems using conventional

forms of detection. This could be because:

_ there is an access or maintenance problem

_ the protected area is too high and/or may suffer from smoke stratification problems

_ an invisible installation is required

_ the environmental conditions are extreme (hot, cold, dirty, etc)

When specifying or designing an aspirating smoke detection system it is essential to

define the performance required from the system.

System sensitivity:

System sensitivity should be appropriate and realistic.High sensitivity and rapid

response can be achieved from a single detector in a small computer room. Normal

sensitivity and response would be more appropriate when protecting 2000m2 of

warehouse space where height and volume dissipate and dilute the smoke sample.

The total allowable number of sampling points varies for each manufacturer and the

sensitivity at each hole is a function of 'detector' sensitivity and the number of

sampling holes. The more sensitive the detector, the more sampling holes can be

drilled in the pipe network. These systems are based on the assumption that 'any

smoke in the protected area will end up going through the air handling system'.

Sampling points are therefore arranged across the inlet grilles to the air handling units.

As high sensitivity is often required in a high airflow and therefore high

dilution area, a reasonable guideline is to allow for one detector per 1500m3.It is good

practice to use a separate sampling pipe for each air handling unit to balance out as

many pressure variations as possible.If it is necessary to mount the aspirating smoke

detector outside of the protected area the detector exhaust should always be piped

back to the protected area. This will prevent the sampled air, and perhaps smoke,

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contaminating other areas and balance any pressure variations between the protected

area and the detector location

Because many air handling units add a percentage of fresh air, a Reference

Detector should be considered to prevent false alarms caused by external pollution

entering with the ‘fresh’ air. The Reference Detector monitors the incoming fresh air

and ‘offsets’ the alarm thresholds of other Detectors if polluted air is detected.

This will help prevent false alarms occurring from this source.

Secondary sampling systems generally have sampling points positioned in

the same locations and using the same design criteria as normal detectors . Where

enhanced or high sensitivity systems are required the normal area coverage per

detector (sampling point) should be reduced .Because more heat is required to lift

smoke to great heights the amount of smoke that can reach high level areas can be

minimal if the fire is small .Where protection is provided to high level racking it may

be necessary to install multiple levels of sampling points to achieve best performance

as smouldering fires produce a relatively small amount of heat.

Where the aspirating detection system is the sole form of protection in any

given area, it is inappropriate to use a sequential sampling system (as adjacent areas

would lose their protection while the system sequences through its cycle). Modern

intelligent aspirating detection systems are often used in adverse environments where

site conditions cause unusual effects. Many diverse areas can be protected as hot air

can be cooled down, cold air warmed up, dusty air filtered, dirty air recognised as part

of normal operating conditions and contaminated air returned back to where it was

sampled from. In such applications it is important to site the detector in a more

environmentally friendly area and ensure that the sampling pipe network is

constructed from a suitable material.

Aspirating smoke detection is a very effective method of smoke detection. It

may be useful to note the following points when protecting unusual areas:

_ Atria / High Areas:

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Atria have stratification layers that vary with seasonal temperatures, making it

difficult to predict the optimum level(s) for best detection.

This type of area often benefits from a 3D approach with vertical sampling in

addition to the normal area coverage. This vertical sampling should be at 3m or 2°C

intervals. At each vertical sampling position an attempt should also be made to

maintain coverage in the horizontal plane.

_ Restricted Access / Containment Areas:

Some areas may be difficult to gain normal access to, either because of high security

or because the protected area is a health hazard. Such areas can often be protected

with aspirating systems where the detector is sited outside the problem area. This

minimises any required maintenance access into the protected area. It is important to

pipe the detector exhaust back to the protected area to prevent contamination

_ Dusty Areas:

These areas can be protected by detectors that contain dust recognition systems and/or

filter out dust particles. Contaminated filters reduce the performance of the system

and provision should be made to ensure a consistent level of protection

_ Hot Areas:

Most aspirating smoke detectors are designed to operate below 60°C.If the air sample

is above this temperature, the detector may be sited remotely and the air sample

cooled by either extending the pipe length or running it through a heat exchanger

(water jacket).

Size of the sampling holes:

The size of sampling holes will vary for each system and can be optimised using the

manufacturers computer software modelling packages. The sensitivity of each

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sampling point is proportional to the amount of air-flow through it and there are two

approaches to take with regard to sampling point hole sizing:

_ Identical sampling hole sizes –

This makes it easy for site engineers as all holes are the same, but means that each

sampling point will have a different sensitivity.This is because the air-flow through

each sampling hole will be affected by the pressure gradient down the main pipe

run(s). The holes closest to the detector will draw most air and therefore be more

sensitive.

_ Varying sampling hole sizes –

This requires additional care from site engineers, but also means that each sampling

point will draw similar quantities of air and therefore have a similar sensitivity.

Most aspirating smoke detectors have multiple alarm levels and consideration

should be given to best utilizing them.

VESDA Air Sampling System:

The VESDA system uses a Xenon tube as the light source to bounce light, off fire

byproducts in the detection chamber.

The VESDA air sampling fire detection system detects the invisible byproducts

of materials as they degrade during the pre-combustion stages of an incipient fire.

And, by actively and continuously sampling air, the system operates independently of

air movements.

Operation:

Air samples are continuously drawn from the monitored environment, typically

through a sampling pipe network with the aid of a high efficiency aspirator. On the

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way to the fire detector the air samples pass through a filter assembly to screen out

large airborne dust particles. Once inside the air sampling detector the samples are

exposed to a high-intensity and broad-spectrum light source. The incident light

scattered from smoke particles in the air sample passes through a series of optical

components to a solid state light receiver. The light is converted to an electronic

signal and passed to the control system.

At the control module the signal is processed and presented on an analog bar

graph to visually indicate the level of smoke present in the monitored area. Depending

upon smoke levels and the preprogrammed alarm levels, the appropriate output

signals are generated.

The first of the three staged alarm levels (ALERT) may simply indicate that the

system has detected something out of the ordinary that should be investigated. The

second level (ACTION) indicates that a potential fire exists and that emergency

procedures should begin. The third level (FIRE) signifies an actual fire condition.

AIR SAMPLING SYSTEMS USING LASER TECHNOLOGY:

1. Analaser air sampling system.

2.Stratos-Micra

AnaLASER Air Sampling System

Early detection means catching a fire in its incipient stages. That's enough time to

Analyze the situation

Alert personnel

Shut down equipment

Remove the source of the fire

Control the activation of the fire

suppression system

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ANALASER is used where Early Warning is Critical to Protect High-value Assets

such as:

Telecommunications

Computer Rooms .

Today's sophisticated telecommunications, computer, and business

systems are so vital that even a minor interruption in their operation, or loss of data,

could create serious or even crippling financial losses or life safety dangers. The

electronic hardware found in such installations is highly vulnerable to fire and can be

seriously affected by increases in temperature or contamination from smoke or

corrosive gases. in these and other areas such as museums, electronic manufacturing

facilities, or anechoic chambers where high-value property is present, AnaLASER

Advanced Technology Smoke Detection provides the early warning signs that can

spell the difference between a minor inconvenience and a major catastrophe.

When Conventional Detectors Won't Work Properly in

Clean Rooms

Atriums

High-Bay Warehouses

Nuclear Facilities

In order for a smoke detector to work properly, smoke in a concentration

sufficient to trigger an alarm must get to the detector. In many cases, this may take so

long and involve a fire of such magnitude that conventional detectors are virtually

useless. High-bay warehouses, where detectors are physically far removed from

sources of combustion, clean room with laminar airflow and rapid air changes that

dilute smoke, atriums, and other areas where conventional detectors may be rendered

inoperable by damage or vandalism, require the high-sensitivity and active air

sampling of AnaLASER Advanced Technology Smoke Detection.

Features of Analaser:

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Active System:- Continually Draws Air

Unlike conventional smoke detectors that passively wait for smoke to reach

them, the AnaLASER System continuously draws air from the protected area through

a piping network to the detection chamber. The pipe diameter and hole size in the

piping are optimized using the proprietary Factory Mutual-approved "SNIFF"

computer program to achieve equal sensitivity at all sampling points and minimum air

transport time.

Designed to Eliminate False Alarms:

With conventional, flashing Xenon tube, high-sensitivity devices, large

particles such as dust give "false" alarm signals if a filter is not used. The AnaLASER

Detector incorporates a particle size discriminator which eliminates such false

indications and allows the device to react only to those particles which fall into the

predetermined size ranges of smoke. In addition to this ability to discriminate between

particle sizes, the AnaLASER built-in data logger gathers information on minimum

and maximum ambient particle concentrations for accurate setting of the system's

three independently programmable alarm levels.

Up to 1000X More Sensitive Than Conventional Smoke Detectors:

AnaLASER Advanced Technology Smoke Detection will detect highly

diluted smoke and other overheat by-products at concentrations as low as 0.003%

obscuration per foot (0.01% obscuration per meter) compared to 3.0% obscuration per

foot for conventional smoke detectors. The combination of the ability to detect the

smallest smoke particles and the active airflow sampling network provides the earliest

possible recognition of an incipient fire.

Earliest Detection of Overheat Conditions:

Studies have shown that as electrical or electronic wire begins to overheat, it

releases specific materials as the temperature increases. AnaLASER has been proven

to detect the "plasticizers “ commonly released from PVC wire in the very early

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phases of heat buildup even before hydrogen Chloride (HCl) or pyrolysed

byproducts. It is precisely this ability to detect plasticizers that gives AnaLASER the

capability to provide earliest possible detection of an overheat situation.

Avoid Unnecessary Release of Suppression Agent

The ability to set three independently programmable alarm levels ,

ALARM,ALERT,FIRE allows time for preventative actions . The level three alarm

would indicate an actual fire may exist and initiate any number of actions from

notification of authorities to release of suppression agents. It is this series of alarm

levels that allows preventative action and avoid unnecessary release of agents.

Laser Detection

Laser Particle Counter

No Filter

No Expensive Refurbishing

Discriminates

No Degradation

The Analaser uses a laser beam and a particle discriminator to detect fire and reject

false alarms.

Operation:

The AnaLASER Detector consists of three main components; an air plenum chamber

with a centrifugal fan, a detection chamber with a focused 100 micron diameter laser

beam, and a single photon avalanche diode (SPAD) sensor. A powerful high-

efficiency centrifugal fan draws air continuously from the protected area into the

piping network and through the detection chamber without filtration or flow

restriction.A laser beam bounces light off small particles released by the combusting

materials in the protected area As a result, filter maintenance and loss of sensitivity

due to filter plugging are eliminated.

The SPAD photon sensor detects individual particles of smoke as they pass

through the laser beam. Smoke concentration is determined by counting the number

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of discrete particles detected, in a given time period. The system converts this digital

particle count to an analog signal directly proportional to the smoke concentration and

transmits this signal to the Display Control Panel.

The detector incorporates a particle size discriminator that provides outputs

only from particles in the size range of smoke while virtually eliminating outputs

from dust or other airborne contaminants. The laser used in the AnaLASER System is

designed to provide a minimum 10-year life and produce a long-term, stable output.

Changes in laser intensity resulting from temperature fluctuations, component aging,

or contaminant buildup are compensated for electronically. Supervisory circuits

monitor the operation of all critical components. The system also monitors airflow. in

the event of a component malfunction or variation in airflow, a FAULT signal is

automatically transmitted to the Display Control Panel.

This technology creates a high sensitivity smoke detection system up to 1000

times more sensitive than conventional ionization or photoelectric type smoke

detectors.

STRATOS –MICRA 25 AND 100

Stratos-Micras are air sampling smoke detectors.

Stratos-Micra uses the detector chamber from the Stratos-HSSD 2 to provide

the same sensitivity levels. Stratos-Micra 25 is the smallest high sensitivity aspirating

smoke detector available.

Stratos-Micra embodies innovative features which depart from accepted

techniques for detectors which operate at very high sensitivity. Perhaps the most

important feature of the system is the adoption of a patented Perceptive 'Artificial

Intelligence' known as ClassiFire-3D. This controls all aspects of the system

operation. ClassiFire-3D ensures that Stratos-Micra operates at maximum SAFE

sensitivity to give warning of problems earlier than previously considered possible.

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The picture below shows a Stratos-HSSD 2 with a Stratos-Micra 25 and a Stratos-

Micra 100 for size comparison

ClassiFire-3D is the most comprehensive intelligence found in a smoke

detection system to date. Not only does it determine the maximum reliable sensitivity

for the environment, but it also controls the dust separator monitoring for maximum

efficiency.

The detection principle used in Stratos-Micra is known as ' forward light

scattering' where the laser beam is diffracted by a small angle by smoke particles.

This principle not only offers high sensitivity, but sensitivity to a wide range of

Particle sizes.

A patented feature of the system is that compensation is made for any contamination

in electronic circuitry or hardware, ensuring a long and trouble free life.

The Stratos range of detectors are the only high sensitivity systems which are

routinely applied to the protection of very dirty and dusty environments. This is

achieved by using Laser Dust Discrimination (LDD) with a patented dust

management and separator system. These features have greatly extended separator life

service intervals. At the other extreme, Stratos-Micra 25 is capable of providing the

very highest levels of sensitivity in environments such as computer and clean rooms.

In these applications it is able to sense the very smallest amounts of smoke.

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Use of the latest semiconductor laser, electronic components and

manufacturing techniques enable the Stratos-Micra 25 system to be supplied and

installed with a significantly lower whole-life cost then alternative high sensitivity

systems.

Design Limitations:

Stratos-Micra 25 is intended to provide LOCALISED incipient fire detection only.

This means that it is suitable for the substantial range of applications typified by;

small non-compartmentalised rooms, warehouse racking, or pieces of electronic or

electromechanical equipment where it is desirable to achieve individual incipient fire

reporting. In compartmentalised rooms, each compartment would normally use

individual Stratos-Micra 25 detectors.

This product employs a very low-power aspirator and the aspirating capability

of the Stratos-Micra 25 detector is limited accordingly. Stratos-Micra 25 is NOT

intended to protect large areas, or to sample from areas where there may be any

difference in airflow rates or pressure differentials. Application of Stratos-Micra 25 in

these circumstances is not recommended. If detection in environments conforming to

these descriptions is required, alternative versions of Stratos products should be used.

It is recommended that a maximum sampling pipe length of 25 metres to be

used on the Stratos-Micra 25. Maximum single length of sampling pipe to be used on

the Stratos-Micra 100 detector is 100 metres in STILL AIR with 10 sampling holes

(or Capillary Remote Sampling Points). This will provide a transport time from the

end of the sampling pipe within 120 seconds. If the protected area has airflow present

the maximum permitted sampling pipe length will be reduced. In areas or applications

where the airflow rate exceeds 1 metre per second, maximum sampling pipe length is

reduced to 10 metres.

Stratos-Micra 100 has two pipe inlets and supports a maximum of 100 metres of

sampling pipe. Stratos-Micra is available with an optional ‘Piped Exhaust’ type

Docking Station. This is primarily intended to allow the Stratos-Micra detector to

sample from areas which may be at different air pressure to the detector location..

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Stratos-Micra provides four alarm level outputs and a fault output to the

fire alarm panel. Relays for Fire 1 and Fault are fitted as standard. When an

addressable panel is used the Addressable Protocol Interface Card (APIC) is used to

communicate using the addressable protocol. Using the APIC means that the alarm

and fault relays can be used for other purposes.

Specifications of Stratos-Micra 25:

Supply voltage: 21.6 - 26.4 Volts DC.

Current consumption: 250mA at 24 Volts DC.

Size: 135W x 175H x 80D.

Weight: 1.01 kg.

Operating temperature

range:  

-10 to +60 deg.

Centigrade.

Operating humidity

range:

0-90% R.H. non

condensing.

Sensitivity

range(Obsc/m):

Min = 25% Max =

0.03%.

Particle sensitivity

range:0.003 to 10 microns.

Sampling pipe length:50 metres max. 25 metres

recommended

Cabinet rating: IP50.

“ PINNACLE ”

THE ULTRA HIGH SENSITIVE LASER SMOKE DETECTOR

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Pinnacle, from System Sensor is an intelligent, addressable spot type smoke detector,

which is a laser-based and microprocessor controlled detector, achieving the highest

sensitivity and stability possible .

Laser Systems employing Pinnacle can be extremely flexible and cost

effective. Only critical areas that actually require ultra high sensitivity smoke

detection will use Pinnacle. Non-critical areas can simply use standard photoelectric

or ionization smoke detectors. But, regardless of type, all of the detectors install in the

same mounting bases. No special equipment is needed in order to install Pinnacle.

Pinnacle supercedes the performance of aspirated smoke detection systems:

In many ways, Pinnacle supercedes the performance of aspirated smoke detection

systems, traditionally the only way to achieve high sensitivity smoke detection.

Aspirated systems operate by drawing air and smoke through a network of pipe or

tubing that is routed throughout the protected space. Because of the nature of

detecting smoke in this way, aspirated systems are subject to the effects of dilution.

During an actual fire, smoke is drawn into the pipe through one of its sampling

ports. Unfortunately, the other sampling ports continue to draw clean air into the pipe

from areas that the smoke has not reached. This means that the smoke sensor in an

aspirated system must be set more sensitive to offset the effects of dilution.

Because Pinnacle is a spot-type smoke detector, it is not susceptible to

dilution. It is able to provide the exact location of the fire by identifying the address of

the detector sensing the smoke. This can greatly reduce response time in a real fire

situation since smoke at such low levels is not visible to the human eye. In addition,

each detector in a Pinnacle smoke detection system is fully supervised.

The main parts in a Pinnacle are:

Laser Diode

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Optical Amplifier

Photo Receiver

Laser Beam

The working of Pinnacle:

The principles of laser detection are similar to those of photoelectric technology. In a

photoelectric smoke detector, a Light Emitting Diode (LED) emits light into a sensing

chamber that is designed to completely restrict ambient light while allowing smoke to

enter. Any particles of smoke entering the chamber will scatter the light and trigger

the photodiode sensor.

Pinnacle works on the same light-scattering principle, but with 100 times

greater sensitivity. This ultra-sensitivity is due to the laser itself, which is literally

amplified light (the word “laser” is an acronym for Light Amplification by Stimulated

Emission of Radiation).

Using an extremely bright, controlled laser diode, the laser beam is

transmitted through the chamber to a light trap that eliminates any reflection.If a

particle of smoke (or dust) enters the chamber, light from the laser is scattered and the

detector, using patented algorithms, verifies the nature of the scattered light to

determine whether the source is dust or smoke. If a determination of smoke is made,

the alarm is signaled.

Smoke particles, especially those by-products of an early fire, are

extremely small, hence the need for the high sensitivity of the laser.

Pinnacle Specifications

Voltage Range : 15 – 32 volts DC peak

Standby Current (max. avg.) : 230 µA @ 24 VDC (without communication)

330 µA @ 24 VDC (one communication every 5 sec)

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LED Current (max.) : 6.5 mA @ 24 VDC (on)

Operating Temperature Range : 32° to 100°F (0° to 38°C)

Velocity Range : 0 – 4000 fpm (0 to 20.3 m/s)

Relative Humidity : 10% – 93% noncondensing

Smoke Sensitivity (9 levels) :0.02, 0.03, 0.05, 0.10, 0.20, 0.50, 1.00, 1.50,

2.00%/ feet obscuration.

(0.06, 0.10, 0.16, 0.33, 0.66, 1.65, 3.24, 4.85,

6.41 %/m obscuration.

MULTICRITERIA SMOKE DETECTOR ESM12251TEM

ESM1225TEM is a true multicriteria detector with microprocessor at its heart .

There is a combination of optical smoke sensing chamber and thermal sensing

element in the detector . Detector issues an addressable fire alarm , prewarning , fault

warning and maintainence warning.

Special algorithms ‘Drift compensation ‘ and smoothing element nuisance

alarms provide a consistent progressive alarm sensitivity threshold .The first feature

compensates automatically for the build up of contaminants in the sensing chamber

keeping the sensitivity constant up to a defined maximum level. Smoothing takes into

account short term environmental noise effects. When detector needs cleaning , it will

give an addressable service alarm.

Two LEDs provide information of alarms and are visible to all

directions.Detector has 2 rotary switches for addressing of the detector.Detector is

easy to install, it is placed into its base and turned into position.

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Technical specifications:

Dimensions 102x43mm

Operating temperature -30C-+60C

Humidity 10-93+/-2%

Operating voltage 15-32V DC

Standby current 250-300microAmp

Infra-Red BeamMaster-H Smoke Detector

The Chubb BeamMaster-H Smoke Beam Detector consists of a wall mounted emitter

and receiver pair incorporating a near infra-red beam to detect smoke using the light

obscuration method.

The Chubb BeamMaster-H Smoke Detector is designed for detection of

smoke in large spaces such as halls, warehouses, museums, theatres etc., where point

detection is impractical or more costly. The unit detects smoke linearly over the

protected range enabling early detection before the fire spreads.

Operation :

The emitter projects a near Infra-red beam which is detected by the receiver . The

beam is pulsed to reduce the overall current consumption and improve the noise

rejection characteristics. Powered directly from the Zonemaster conventional zone

without the need for an external supply , when the zone is reset , the detector is

automatically reset.

The emitter and receiver are synchronised via a direct 2 wire link which

also supplies power to the emitter. All other field wiring is connected to the interface

on the receiver. If smoke obscures the beam the receiver detects this and indicates a

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fire. Any gradual reduction in received light through environmental contamination is

automatically compensated for within the detector.

In normal operation two status LEDs indicate a fire or fault condition, these are

viewed through a unique lens that allows good visibility from any viewing angle

particularly from beneath the unit. An output is also provided from the receiver for a

remote fire indication.

The unit indicates a fault on the zone under the following conditions:

Compensation limit exceeded

Total Obscuration of Beam (Under this condition a fire signal will also be

generated following a pre-defined time delay.)

Receiver cover left open

Receiver unit removed from zone

Line smoke detector Fireray 1401 based on infrared beam:

Line smoke detectors are used mainly in premises with high ceilings such

as shopping centres, atriums in hotels, churches, hangars, etc., and in rooms in which

detectors cannot or may not be mounted on the ceiling , for example in historical

buildings and museums.

The line smoke detector consists of a transmitter that transmits a modulated infra-red

light beam to a receiver , along with a control unit for power supply and signal

conversion. The received light beam is analysed , and if smoke is present for more

than five seconds, the fire alarm is activated.

Transmitter and receiver should be positioned so that the beam of light runs parallel

with the ceiling at a distance of 0.3 to 0.6 metres. The maximum range is 100m and

coverage is 7m on either side of the beam.

.

Fireay 1401 consists of one transmitter and one receiver in aluminium enclosures of

the dimensions, 128x90x85mm and a 250x200x148mm control unit.

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Video Smoke Detection:

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Due to the size and environmental conditions in some locations , detecting

small amounts of smoke using standard methods of detection may prove

inadequate.A video based fire and smoke detection system will detect fire in the

very early stages in such environments thereby providing the ideal detection

solution.

Features And Benefits:

Upto 8 cameras per system and it can utilise existing CCTV surveillance

cameras. 10 independent alarm zones per camera .

Automatic checking for video signal loss,obscuration, low level light and low

contrast level 5000 event log .

Relays for interfacing with other equipment.

Flexible configuration between camera zones and alarm outputs.

In cavernous environments such as a turbine hall or exhibition halls , detecting

smoke quickly using standard methods of detection can be inadequate.‘Point’ type

or beam’ type detectors may prove to be too slow. Similarly in such environments a

fire may be well under way before being detected by a heat detector. In such

conditions video based smoke detection offers an ideal detection solution.

The Chubb video smoke detection system consists of a standard closed

circuit television (CCTV) cameras linked to a self contained processing system

which is capable of recognizing small amounts of smoke , within the video

image. The system uses highly complex algorithms to process video information

for up to eight cameras simultaneously. Following detection the system operator is

alerted both at the processor and by a variety of remote outputs.

The system can be divided into ten independent alarm zones per camera, giving

80 detection zones per system. The system also has sixteen opto - isolated

alarm outputs that may be individually assigned to any combination of zones and

sectors. These system outputs can be easily interfaced on to our

Controlmaster range of analogue addressable control panels.

Video smoke detection can be installed in a variety of applications, such

electrical power generating stations , toxic waste plants , cement works , paper

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mills , aircraft hangers , road and rail tunnels and historic buildings.

Alarm output devices:

Upon receiving an alarm notification, the fire alarm control panel must now tell

someone that an emergency is underway. This is the primary function of the alarm

output aspect of a system. Occupant signaling components include various audible

and visual alerting components, and are the primary alarm output devices. Bells are

the most common and familiar alarm sounding device, and are appropriate for most

building applications. Horns are another option, and are especially well suited to areas

where a loud signal is needed such as library stacks, and architecturally sensitive

buildings where devices need partial concealment. Chimes may be used where a soft

alarm tone is preferred, such as health care facilities and theaters. Speakers are the

fourth alarm sounding option, which sound a reproducible signal such as a recorded

voice message. They are often ideally suited for large, multistory or other similar

buildings where phased evacuation is preferred. Speakers also offer the added

flexibility of emergency public address announcements. With respect to visual alert,

there are a number of strobe and flashing light devices. Visual alerting is required in

spaces where ambient noise levels are high enough to preclude hearing sounding

equipment, and where hearing impaired occupants may be found..

Another key function of the output function is emergency response notification. The

most common arrangement is an automatic telephone or radio signal that is

communicated to a constantly staffed monitoring center. Upon receiving the alert, the

center will then contact the appropriate fire department, providing information about

the location of alarm. In some instances, the monitoring station may be the police or

fire departments, or a 911 center. In other instances it will be a private monitoring

company that is under contract to the organization. In many cultural properties, the

building's in-house security service may serve as the monitoring center.

Other output functions include shutting down electrical equipment such as computers,

shutting off air handling fans to prevent smoke migration, and shutting down

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operations such as chemical movement through piping in the alarmed area. They may

also activate fans to extract smoke, which is a common function in large atria spaces.

These systems can also activate discharge of gaseous fire or preaction sprinkler

systems.

Smoke Alarm Response:

Smoke alarm response was

measured by direct recording of the

voltage signal from both ionization and

photoelectric smoke alarms arranged for

analog output, instead of the more common

alarm threshold. By recording analog

output, the performance of smoke alarms at

any desired threshold setting as well as the

potential use of algorithms that reduce

nuisance alarms can be evaluated. The

analog signal was calibrated against

unmodified alarms purchased in local, retail

outlets, in the laboratory to verify that the

modifications did not affect the alarm performance. Alarms were located in typical,

code-required locations, as well as in the room of origin, in order to determine the

effectiveness of alternative siting rules. In the room of fire origin, three unmodified

alarms were used to avoid destruction of the limited supply of analog-modified alarms

Interconnecting Smoke Detectors:

Battery-powered smoke detectors are stand-alone units.

Home smoke detectors should be interconnected. This means that an alarm in one

smoke detector will cause all others in the home to go into alarm. Typically the

detectors are connected by a pair of wires to transfer an alarm signal from one

detector to all the others in the chain

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This sort of wiring guarantees that if one alarm in the house goes off, they all

go off. Even if the fire starts and is detected in the basement, people asleep upstairs

will hear the alarm because of this safety feature -- every alarm in the house goes

off.

If we buy an AC-powered smoke detector today, it will have three wires --

black, white and red. Black accepts 120 volts AC, white is neutral, and red is the

intercommunication wire. All of the alarms operate off the same circuit from the fuse

box and are normally connected using normal wire for three-way switches this wiring

contains black, white and red wires in a Romex casing.The red wire is run from alarm

to alarm to interconnect them.

When any alarm detects a fire, it sends a 9-volt signal on the red wire. Any

alarm that detects a 9-volt signal on the red wire will begin sounding its alarm

immediately. Most alarms can handle about a dozen units intercommunicating on the

same red wire. It's a very simple and a very effective system.

Working of three way switches:

This is explained by looking at how a normal light is wired for residential wiring of a

light switch. The figure below shows the simplest possible configuration

In this diagram, the black wire is "hot." That is, it carries the 120-volt AC current. The

white wire is neutral. In the figure the current runs through the switch. The switch

simply opens (off) or closes (on) the connection between the two terminals on the

switch. When the switch is on, current flows along the black wire through the switch

to the light, and then returns to ground through the white wire to complete the circuit.

To run power from the fuse box to the switches and outlets in the house ,a romex wire

is normally used. A piece of Romex is shown here:

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Romex consists of an outer plastic sheath (white in this picture) with

three wires inside. The black and white wires are insulated, while a bare, third wire

acts as the grounding wire for the circuit. Most normal household applications use 12-

or 14-gauge Romex.

Installation of smoke detectors:

Any smoke detector that should be installed should have a test button. When the

button is depressed, the audible alarm sounds the warning signal. If there is a hearing

impaired person in the house, consider the installation of a hearing impaired smoke

detector. These are special units that feature a powerful strobe light to alert the

hearing impaired in the event of a fire.

Smoke detectors should be wired directly to the 120VAC electrical circuits.

Units that depend on batteries as their sole source of power should be avoided.

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References:

1. Mechanical and Industrial Measurements By R.K.Jain.

2. www.msnsearch.com\ smoke detection systems.

3. www.google.com\ laser beam smoke detectors

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