INTRODUCTION TO POLLUTION CONTROL

Has a regulatory agency announced regulations in your industry or declared

your workplace unhealthy? Do your neighbors complain about odors? Do you face the

dilemma of balancing company profitability with the demand to meet environmental

requirements?

This quick guide will explain all the basics of pollution control. It will help

you understand the technologies and prepare you to make informed, knowledgeable

decisions. All defined terms can be found in the Definitions section.  Be sure to visit

the Overview of Emission Control Technologies page once you are comfortable with

the introduction found here.

The first concept to recognize is that many distinctly different industries

have similar pollution problems and solutions. Once you understand the basics, then

we can help you begin to decide which is the best for you. Always contact an Anguil

representative to discuss particular applications and solutions. For now, all that you

need to know is that hazardous air pollutants (HAPs) and Volatile Organic

Compounds (VOCs) are, in fact, harmful to you and the environment. There are

hundreds of science journals and EPA documents that can explain why toluene,

ethanol, and other organic compounds are bad for your health.

1

BLOCK DIAGRAM

Block Diagram: Intelligent pollution control system: Auto ignition cut off for

automotives by detecting Carbon Monoxide level at vehicle’s silencer with audio

visual alert

2

Power supply to all sections

Step down

T/F

Bridge Rectifier

Filter Circuit

Regulator

Music generator for symbolic representation of vehicle ignition

DC input for ignition

DC motor for symbolic representation of vehicle

ignition

Carbon

Monoxide

Sensor

Sensitivity control adjust Transistor

driver circuit

Relay driver circuit Audio

buzzer alert

Ignition control

relay

LED ignition indicator

WORKING PROCEDURE

POWER SUPPLY:

The power supply from socket is connected to the step down transformer in

order to step down the voltage from 230v to 12 or 18v and the output of step down

transformer is 12v 0r 18v ac is connected to rectifier to convert it to pulsating dc from

rectifier we will get 12v 0r 18v pulsating dc. The rectifier output is connected to

capacitive filter of 100 micro farads it will blocks DC and allows total ac

ripples/contents to ground from that we will get pure DC and is given to voltage

regulator to get constant output voltage of 5v.

PROJECT WORKING:

1. Initially the car engine is in on condition i.e., it is default driving which is indicated

by a DC motor running and a continuous on and off of an LED array.

2. The prototype makes use of alcohol sensor to detect the presence of alcohol or

carbon monoxide gas present in the car.

3. Whenever the driver or the person driving the car consumes alcohol, the sensor

senses it and gives a signal to the buzzer for indicating the presence.

4. This indication is also given to the relay which makes the engine of the car to stop.

5. When the car is stopped the LED indication also gets stopped.

6. The sensing and detection of the alcohol present in the car goes on continuously by

the indication of buzzer until and unless the alcohol present gets vanished.

7. Once the alcohol gets vanished the buzzer comes in the initial position i.e it gets

stopped.

8. By using this simple and efficient prototype for the alcohol detection a much

important and costlier life can be saved by avoiding the occurrence of accidents.

3

HARDWARE EXPLANATION

RESISTOR:

Resistors "Resist" the flow of electrical current. The higher the value of

resistance (measured in ohms) the lower the current will be. Resistance is the property

of a component which restricts the flow of electric current. Energy is used up as the

voltage across the component drives the current through it and this energy appears as

heat in the component.

4

Colour coding :

CAPACITOR:

Capacitors store electric charge. They are used with resistors

in timing circuits because it takes time for a capacitor to fill with charge. They are

used to smooth varying DC supplies by acting as a reservoir of charge. They are also

used in filter circuits because capacitors easily pass AC (changing) signals but they

block DC (constant) signals

Circuit symbol:  

5

Electrolytic capacitors are polarized and they must be connected the correct

way round, at least one of their leads will be marked + or -.

Examples:  

DIODES:

Diodes allow electricity to flow in only one direction. The arrow of the circuit

symbol shows the direction in which the current can flow. Diodes are the electrical

version of a valve and early diodes were actually called valves.

Circuit symbol:   

Diodes must be connected the correct way round, the diagram may be

labeled a or + for anode and k or - for cathode (yes, it really is k, not c, for cathode!).

The cathode is marked by a line painted on the body. Diodes are labeled with their

code in small print; you may need a magnifying glass to read this on small signal

diodes.

Example:   

   

LIGHT-EMITTING DIODE (LED):

6

The longer lead is the anode (+) and the shorter lead is the cathode (&minus). In the

schematic symbol for an LED (bottom), the anode is on the left and the cathode is on

the right. Light emitting diodes are elements for light signalization in electronics.

They are manufactured in different shapes, colors and sizes. For their low

price, low consumption and simple use, they have almost completely pushed aside

other light sources- bulbs at first place.

It is important to know that each diode will be immediately destroyed unless

its current is limited. This means that a conductor must be connected in parallel to a

diode. In order to correctly determine value of this conductor, it is necessary to know

diode’s voltage drop in forward direction, which depends on what material a diode is

made of and what colors it is. Values typical for the most frequently used diodes are

shown in table below: As seen, there are three main types of LEDs. Standard ones get

full brightness at current of 20mA. Low Current diodes get full brightness at ten

time’s lower current while Super Bright diodes produce more intensive light than

Standard ones.

7

Since the 8052 microcontrollers can provide only low input current and since

their pins are configured as outputs when voltage level on them is equal to 0, direct

confectioning to LEDs is carried out as it is shown on figure (Low current LED,

cathode is connected to output pin).

SWITCHES AND PUSHBUTTONS:

A push button switch is used to either close or open an electrical circuit

depending on the application. Push button switches are used in various applications

such as industrial equipment control handles, outdoor controls, mobile

communication terminals, and medical equipment, and etc. Push button switches

generally include a push button disposed within housing. The push button may be

depressed to cause movement of the push button relative to the housing for directly or

indirectly changing the state of an electrical contact to open or close the contact. Also

included in a pushbutton switch may be an actuator, driver, or plunger of some type

that is situated within a switch housing having at least two contacts in communication

with an electrical circuit within which the switch is incorporated.

Typical actuators used for contact switches include spring loaded force cap

actuators that reciprocate within a sleeve disposed within the canister. The actuator is

typically coupled to the movement of the cap assembly, such that the actuator

translates in a direction that is parallel with the cap. A push button switch for a data

input unit for a mobile communication device such as a cellular phone, a key board

for a personal computer or the like is generally constructed by mounting a cover

member directly on a circuit board. Printed circuit board (PCB) mounted pushbutton

switches are an inexpensive means of providing an operator interface on industrial

control products. In such push button switches, a substrate which includes a plurality

of movable sections is formed of a rubber elastomeric. The key top is formed on a top

8

surface thereof with a figure, a character or the like by printing, to thereby provide a

cover member. Push button switches incorporating lighted displays have been used in

a variety of applications. Such switches are typically comprised of a pushbutton, an

opaque legend plate, and a back light to illuminate the legend plate.

DESCRIPTION OF BLOCK DIAGRAM

BLOCK DIAGRAM FOR REGULATED POWER SUPPLY (RPS):

Figure: Power Supply

TRANSFORMER:

A transformer is a device that transfers electrical energy from one circuit to

another through inductively coupled conductors—the transformer's coils. A varying

current in the first or primary winding creates a varying magnetic flux in the

transformer's core, and thus a varying magnetic field through the secondary winding.

9

This varying magnetic field induces a varying electromotive force (EMF) or "voltage"

in the secondary winding. This effect is called mutual induction.

Figure: Transformer Symbol

(Or)

Transformer is a device that converts the one form energy to another form of

energy like a transducer.

Figure: Transformer

BASIC PRINCIPLE:

A transformer makes use of Faraday's law and the ferromagnetic

properties of an iron core to efficiently raise or lower AC voltages. It of course

cannot increase power so that if the voltage is raised, the current is

proportionally lowered and vice versa.

10

Figure: Basic Principle

TRANSFORMER WORKING:

A transformer consists of two coils (often called 'windings') linked by an iron

core, as shown in figure below. There is no electrical connection between the coils;

instead they are linked by a magnetic field created in the core.

Figure: Basic Transformer

Transformers are used to convert electricity from one voltage to another with

minimal loss of power. They only work with AC (alternating current) because they

require a changing magnetic field to be created in their core. Transformers can

increase voltage (step-up) as well as reduce voltage (step-down).

Alternating current flowing in the primary (input) coil creates a continually

changing magnetic field in the iron core. This field also passes through the secondary

(output) coil and the changing strength of the magnetic field induces an alternating

voltage in the secondary coil. If the secondary coil is connected to a load the induced

11

voltage will make an induced current flow. The correct term for the induced voltage is

'induced electromotive force' which is usually abbreviated to induced e.m.f.

The iron core is laminated to prevent 'eddy currents' flowing in the core. These

are currents produced by the alternating magnetic field inducing a small voltage in the

core, just like that induced in the secondary coil. Eddy currents waste power by

needlessly heating up the core but they are reduced to a negligible amount by

laminating the iron because this increases the electrical resistance of the core without

affecting its magnetic properties.

Transformers have two great advantages over other methods of changing voltage:

1. They provide total electrical isolation between the input and output, so they

can be safely used to reduce the high voltage of the mains supply.

2. Almost no power is wasted in a transformer. They have a high efficiency

(power out / power in) of 95% or more.

CLASSIFICATION OF TRANSFORMER:

Step-Down Transformer

Step-Up Transformer

Step-down transformer:

Step down transformers are designed to reduce electrical voltage. Their

primary voltage is greater than their secondary voltage. This kind of transformer

"steps down" the voltage applied to it. For instance, a step down transformer is needed

to use a 110v product in a country with a 220v supply.

Step down transformers convert electrical voltage from one level or phase

configuration usually down to a lower level. They can include features for electrical

isolation, power distribution, and control and instrumentation applications. Step down

transformers typically rely on the principle of magnetic induction between coils to

convert voltage and/or current levels.

12

Step down transformers are made from two or more coils of insulated wire

wound around a core made of iron. When voltage is applied to one coil (frequently

called the primary or input) it magnetizes the iron core, which induces a voltage in the

other coil, (frequently called the secondary or output). The turn’s ratio of the two sets

of windings determines the amount of voltage transformation.

Figure: Step-Down Transformer

An example of this would be: 100 turns on the primary and 50 turns on the secondary, a ratio of 2 to 1.

Step down transformers can be considered nothing more than a voltage ratio device.

With step down transformers the voltage ratio between primary and secondary

will mirror the "turn’s ratio" (except for single phase smaller than 1kva which have

compensated secondary). A practical application of this 2 to 1 turn’s ratio would be a

480 to 240 voltage step down. Note that if the input were 440 volts then the output

would be 220 volts. The ratio between input and output voltage will stay constant.

Transformers should not be operated at voltages higher than the nameplate rating, but

may be operated at lower voltages than rated. Because of this it is possible to do some

non-standard applications using standard transformers.

Single phase step down transformers 1kva and larger may also be reverse

connected to step-down or step-up voltages. (Note: single phase step up or step down

transformers sized less than 1 KVA should not be reverse connected because the

secondary windings have additional turns to overcome a voltage drop when the load is

applied. If reverse connected, the output voltage will be less than desired.)

13

Step-Up Transformer:

A step up transformer has more turns of wire on the secondary coil, which

makes a larger induced voltage in the secondary coil. It is called a step up transformer

because the voltage output is larger than the voltage input.

Step-up transformer 110v 220v design is one whose secondary voltage is

greater than its primary voltage. This kind of transformer "steps up" the voltage

applied to it. For instance, a step up transformer is needed to use a 220v product in a

country with a 110v supply.

A step up transformer 110v, 220v converts alternating current (AC) from one

voltage to another voltage. It has no moving parts and works on a magnetic

induction principle; it can be designed to "step-up" or "step-down" voltage. So a step

up transformer increases the voltage and a step down transformer decreases the

voltage.

The primary components for voltage transformation are the step up

transformer core and coil. The insulation is placed between the turns of wire to

prevent shorting to one another or to ground. This is typically comprised of Mylar,

nomex, Kraft paper, varnish, or other materials. As a transformer has no moving parts, it

will typically have a life expectancy between 20 and 25 years.

Figure: Step-Up Transformer

APPLICATIONS:

Generally these Step-Up Transformers are used in industries applications

only.

14

TYPES OF TRANSFORMER:

Mains Transformers:

Mains transformers are the most common type.  They are designed to reduce

the AC mains supply voltage (230-240V in the UK or 115-120V in some countries)

to a safer low voltage. The standard mains supply voltages are officially 115V and

230V, but 120V and 240V are the values usually quoted and the difference is of no

significance in most cases.

Figure: Main Transformer

To allow for the two supply voltages mains transformers usually have two

separate primary coils (windings) labeled 0-120V and 0-120V. The two coils are

connected in series for 240V (figure 2a) and in parallel for 120V (figure 2b). They

must be wired the correct way round as shown in the diagrams because the coils must

be connected in the correct sense (direction):

Most mains transformers have two separate secondary coils (e.g. labeled 0-

9V, 0-9V) which may be used separately to give two independent supplies, or

15

   

connected in series to create a center-tapped coil (see below) or one coil with double

the voltage.

Some mains transformers have a centre-tap halfway through the secondary

coil and they are labeled 9-0-9V for example. They can be used to produce full-wave

rectified DC with just two diodes, unlike a standard secondary coil which requires

four diodes to produce full-wave rectified DC.

A mains transformer is specified by:

1. Its secondary (output) voltages Vs.

2. Its maximum power, Pmax, which the transformer can pass, quoted in VA (volt-

amp). This determines the maximum output (secondary) current, Imax...

Where Vs is the secondary voltage.  If there are two secondary coils the maximum

power should be halved to give the maximum for each coil.

3. Its construction - it may be PCB-mounting, chassis mounting (with solder

tag connections) or steroidal (a high quality design).

Audio Transformers:

Audio transformers are used to convert the moderate voltage, low current output of an audio amplifier to the low voltage, high current required by a loudspeaker.  This use is called 'impedance matching' because it is matching the high impedance output of the amplifier to the low impedance of the loudspeaker.

Figure: Audio transformer

Radio Transformers:

16

Radio transformers are used in tuning circuits. They are smaller than mains and audio transformers and they have adjustable ferrite cores made of iron dust. The ferrite cores can be adjusted with a non-magnetic plastic tool like a small screwdriver. The whole transformer is enclosed in an aluminum can which acts as a shield, preventing the transformer radiating too much electrical noise to other parts of the circuit.

Figure: Radio Transformer

Turns Ratio and Voltage:

The ratio of the number of turns on the primary and secondary coils

determines the ratio of the voltages...

...where Vp is the primary (input) voltage, Vs is the secondary (output) voltage, Np is

the number of turns on the primary coil, and Ns is the number of turns on the

secondary coil.

RECTIFIER:

The purpose of a rectifier is to convert an AC waveform into a DC waveform

(OR) Rectifier converts AC current or voltages into DC current or voltage.  There are

two different rectification circuits, known as 'half-wave' and 'full-wave' rectifiers. 

Both use components called diodes to convert AC into DC.

The Half-wave Rectifier:

The half-wave rectifier is the simplest type of rectifier since it only uses one diode, as shown in figure.

17

Figure: Half Wave Rectifier

Figure 2 shows the AC input waveform to this circuit and the resulting output. 

As you can see, when the AC input is positive, the diode is forward-biased and lets

the current through.  When the AC input is negative, the diode is reverse-biased and

the diode does not let any current through, meaning the output is 0V.  Because there is

a 0.7V voltage loss across the diode, the peak output voltage will be 0.7V less than

Vs.

Figure: Half-Wave Rectification

While the output of the half-wave rectifier is DC (it is all positive), it would

not be suitable as a power supply for a circuit.  Firstly, the output voltage continually

varies between 0V and Vs-0.7V, and secondly, for half the time there is no output at

all. 

The Full-wave Rectifier:

The circuit in figure 3 addresses the second of these problems since at no time

is the output voltage 0V.  This time four diodes are arranged so that both the positive

and negative parts of the AC waveform are converted to DC.  The resulting waveform

is shown in figure 4.

18

Figure: Full-Wave Rectifier

Figure: Full-Wave Rectification

When the AC input is positive, diodes A and B are forward-biased, while

diodes C and D are reverse-biased.  When the AC input is negative, the opposite is

true - diodes C and D are forward-biased, while diodes A and B are reverse-biased.

While the full-wave rectifier is an improvement on the half-wave rectifier, its

output still isn't suitable as a power supply for most circuits since the output voltage

still varies between 0V and Vs-1.4V.  So, if you put 12V AC in, you will 10.6V DC

out

CAPACITOR FILTER:

The capacitor-input filter, also called "Pi" filter due to its shape that looks

like the Greek letter pi, is a type of electronic filter. Filter circuits are used to remove

unwanted or undesired frequencies from a signal.

19

Figure: Capacitor Filter

A typical capacitor input filter consists of a filter capacitor C1, connected

across the rectifier output, an inductor L, in series and another filter capacitor

connected across the load.

1. The capacitor C1 offers low reactance to the AC component of the rectifier

output while it offers infinite reactance to the DC component. As a result the capacitor

shunts an appreciable amount of the AC component while the DC component

continues its journey to the inductor L

2. The inductor L offers high reactance to the AC component but it offers almost

zero reactance to the DC component. As a result the DC component flows through the

inductor while the AC component is blocked.

3. The capacitor C2 bypasses the AC component which the inductor had failed to

block. As a result only the DC component appears across the load RL.

Figure: Centered Tapped Full-Wave Rectifier with a Capacitor Filter

VOLTAGE REGULATOR:

20

A voltage regulator is an electrical regulator designed to automatically

maintain a constant voltage level. It may use an electromechanical mechanism, or

passive or active electronic components. Depending on the design, it may be used to

regulate one or more AC or DC voltages. There are two types of regulator are they.

Positive Voltage Series (78xx) and

Negative Voltage Series (79xx)

78xx:

’78’ indicate the positive series and ‘xx’ indicates the voltage rating. Suppose

7805 produces the maximum 5V.’05’indicates the regulator output is 5V.

79xx:

’78’ indicate the negative series and ‘xx’ indicates the voltage rating. Suppose

7905 produces the maximum -5V.’05’indicates the regulator output is -5V.

These regulators consists the three pins there are

Pin1: It is used for input pin.

Pin2: This is ground pin for regulator

Pin3: It is used for output pin. Through this pin we get the output.

Figure: Regulator

RELAYS:

A relay is an electrically controllable switch widely used in industrial controls,

automobiles and appliances.

The relay allows the isolation of two separate sections of a system with two

different voltage sources i.e., a small amount of voltage/current on one side can

handle a large amount of voltage/current on the other side but there is no chance that

these two voltages mix up.

Inductor

21

Fig: Circuit symbol of a relay

OPERATION:

When a current flow through the coil, a magnetic field is created around the

coil i.e., the coil is energized. This causes the armature to be attracted to the coil. The

armature’s contact acts like a switch and closes or opens the circuit. When the coil is

not energized, a spring pulls the armature to its normal state of open or closed. There

are all types of relays for all kinds of applications.

Fig: Relay Operation and use of protection diodes

Transistors and ICs must be protected from the brief high voltage 'spike'

produced when the relay coil is switched off. The above diagram shows how a signal

diode (eg 1N4148) is connected across the relay coil to provide this protection. The

diode is connected 'backwards' so that it will normally not conduct. Conduction

occurs only when the relay coil is switched off, at this moment the current tries to

flow continuously through the coil and it is safely diverted through the diode. Without

the diode no current could flow and the coil would produce a damaging high voltage

'spike' in its attempt to keep the current flowing.

In choosing a relay, the following characteristics need to be considered:

1. The contacts can be normally open (NO) or normally closed (NC). In the NC type,

the contacts are closed when the coil is not energized. In the NO type, the contacts are

closed when the coil is energized.

22

2. There can be one or more contacts. i.e., different types like SPST (single pole

single throw), SPDT (single pole double throw) and DPDT (double pole double

throw) relay.

3. The voltage and current required to energize the coil. The voltage can vary from a

few volts to 50 volts, while the current can be from a few milliamps to 20milliamps.

The relay has a minimum voltage, below which the coil will not be energized. This

minimum voltage is called the “pull-in” voltage.

4. The minimum DC/AC voltage and current that can be handled by the contacts. This

is in the range of a few volts to hundreds of volts, while the current can be from a few

amps to 40A or more, depending on the relay.

A relay is used to isolate one electrical circuit from another. It allows a low

current control circuit to make or break an electrically isolated high current circuit

path. The basic relay consists of a coil and a set of contacts. The most common relay

coil is a length of magnet wire wrapped around a metal core. When voltage is applied

to the coil, current passes through the wire and creates a magnetic field. This magnetic

field pulls the contacts together and holds them there until the current flow in the coil

has stopped. The diagram below shows the parts of a simple relay.

Figure: Relay

Operation:

When a current flows through the coil, the resulting magnetic field attracts an

armature that is mechanically linked to a moving contact. The movement either makes

or breaks a connection with a fixed contact. When the current is switched off, the

armature is usually returned by a spring to its resting position shown in figure 6.6(b).

Latching relays exist that require operation of a second coil to reset the contact

position.

By analogy with the functions of the original electromagnetic device, a solid-state

relay operates a thyristor or other solid-state switching device with a transformer or

light-emitting diode to trigger it.

23

POLE AND THROW:

SPST SPST relay stands for Single Pole Single Throw relay. Current will only flow

through the contacts when the relay coil is energized.

Figure: SPST Relay

SPDT Relay

SPDT Relay stands for Single Pole Double Throw relay. Current will flow

between the movable contact and one fixed contact when the coil is De-energized and

between the movable contact and the alternate fixed contact when the relay coil is

energized. The most commonly used relay in car audio, the Bosch relay, is a SPDT

relay.

Figure: SPDT Relay

DPST Relay

DPST relay stands for Double Pole Single Throw relay. When the relay coil is

energized, two separate and electrically isolated sets of contacts are pulled down to

make contact with their stationary counterparts. There is no complete circuit path

when the relay is De-energized.

Figure: DPST Relay

DPDT Relay

DPDT relay stands for Double Pole Double Throw relay. It operates like the

SPDT relay but has twice as many contacts. There are two completely isolated sets of

contacts.

24

Figure: DPDT Relay

This is a 4 Pole Double Throw relay. It operates like the SPDT relay but it has 4 sets

of isolated contacts.

Figure: 4 Pole Double Throw relay

TYPES OF RELAY:

1. Latching Relay

2. Reed Relay

3. Mercury Wetted Relay

4. Machine Tool Relay

5. Solid State Relay (SSR)

Latching relay:

Latching relay, dust cover removed, showing pawl and ratchet mechanism.

The ratchet operates a cam, which raises and lowers the moving contact arm, seen

edge-on just below it. The moving and fixed contacts are visible at the left side of the

image.

A latching relay has two relaxed states (bi-stable). These are also called

"impulse", "keep", or "stay" relays. When the current is switched off, the relay

remains in its last state. This is achieved with a solenoid operating a ratchet and cam

mechanism, or by having two opposing coils with an over-center spring or permanent

magnet to hold the armature and contacts in position while the coil is relaxed, or with

a remnant core. In the ratchet and cam example, the first pulse to the coil turns the

relay on and the second pulse turns it off. In the two coil example, a pulse to one coil

turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay

has the advantage that it consumes power only for an instant, while it is being

25

switched, and it retains its last setting across a power outage. A remnant core latching

relay requires a current pulse of opposite polarity to make it change state.

Figure: Latching relay

Reed relay:

A reed relay has a set of contacts inside a vacuum or inert gas filled glass tube,

which protects the contacts against atmospheric corrosion. The contacts are closed by

a magnetic field generated when current passes through a coil around the glass tube.

Reed relays are capable of faster switching speeds than larger types of relays, but

have low switch current and voltage ratings.

Mercury-wetted Relay:

A mercury-wetted reed relay is a form of reed relay in which the contacts

are wetted with mercury. Such relays are used to switch low-voltage signals (one volt

or less) because of their low contact resistance, or for high-speed counting and timing

applications where the mercury eliminates contact bounce. Mercury wetted relays are

position-sensitive and must be mounted vertically to work properly. Because of the

toxicity and expense of liquid mercury, these relays are rarely specified for new

equipment. See also mercury switch.

Machine tool relay:

A machine tool relay is a type standardized for industrial control of machine

tools, transfer machines, and other sequential control. They are characterized by a

large number of contacts (sometimes extendable in the field) which are easily

converted from normally-open to normally-closed status, easily replaceable coils, and

a form factor that allows compactly installing many relays in a control panel.

26

Although such relays once were the backbone of automation in such industries as

automobile assembly, the programmable logic controller (PLC) mostly displaced the

machine tool relay from sequential control applications.

Solid-state relay:

A solid state relay (SSR) is a solid state electronic component that provides a

similar function to an electromechanical relay but does not have any moving

components, increasing long-term reliability. With early SSR's, the tradeoff came

from the fact that every transistor has a small voltage drop across it. This voltage drop

limited the amount of current a given SSR could handle. As transistors improved,

higher current SSR's, able to handle 100 to 1,200 Amperes, have become

commercially available. Compared to electromagnetic relays, they may be falsely

triggered by transients.

Figure: Solid relay, which has no moving parts

SPECIFICATION:

Number and type of contacts – normally open, normally closed, (double-

throw)

Contact sequence – "Make before Break" or "Break before Make". For

example, the old style telephone exchanges required Make-before-break so

that the connection didn't get dropped while dialing the number.

Rating of contacts – small relays switch a few amperes, large contactors are

rated for up to 3000 amperes, alternating or direct current

Voltage rating of contacts – typical control relays rated 300 VAC or 600 VAC,

automotive types to 50 VDC, special high-voltage relays to about 15 000 V

Coil voltage – machine-tool relays usually 24 VAC, 120 or 250 VAC, relays

for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate

27

on a few milli-amperes

APPLICATIONS:

Relays are used:

To control a high-voltage circuit with a low-voltage signal, as in some types of

modems,

To control a high-current circuit with a low-current signal, as in the starter

solenoid of an automobile,

To detect and isolate faults on transmission and distribution lines by opening

and closing circuit breakers (protection relays),

To isolate the controlling circuit from the controlled circuit when the two are

at different potentials, for example when controlling a mains-powered device

from a low-voltage switch. The latter is often applied to control office lighting

as the low voltage wires are easily installed in partitions, which may be often

moved as needs change. They may also be controlled by room occupancy

detectors in an effort to conserve energy,

To perform logic functions. For example, the Boolean AND function is

realized by connecting relay contacts in series, the OR function by connecting

contacts in parallel. Due to the failure modes of a relay compared with a

semiconductor, they are widely used in safety critical logic, such as the control

panels of radioactive waste handling machinery.

As oscillators, also called vibrators. The coil is wired in series with the

normally closed contacts. When a current is passed through the relay coil, the

relay operates and opens the contacts that carry the supply current. This stops

the current and causes the contacts to close again. The cycle repeats

continuously, causing the relay to open and close rapidly. Vibrators are used to

generate pulsed current.

To generate sound. A vibrator, described above, creates a buzzing sound

because of the rapid oscillation of the armature. This is the basis of the electric

bell, which consists of a vibrator with a hammer attached to the armature so it

can repeatedly strike a bell.

28

To perform time delay functions. Relays can be used to act as an mechanical

time delay device by controlling the release time by using the effect of

residual magnetism by means of a inserting copper disk between the armature

and moving blade assembly.

BUZZER:

An electric coil is wound on a plastic bobbin, the latter having a central sleeve

within which a magnetic core is slide ably positioned. One end of the sleeve is closed

and projects beyond the coil. An inverted

cup-shaped housing surrounds the

coil and bobbin and has a central opening

through which the closed end of the sleeve

projects. The core projects into the closed

end of the sleeve beyond the margin of the opening in the housing to augment the

magnetic coupling between the housing and the core. The open end of the housing is

attached to a support bracket of magnetic material, there being a spring between the

bracket and bobbin normally urging the core toward the closed end of the sleeve.

For a self- drive buzzer (DC/ circuit- built), either pizeo or magnetic just apply

the rated current and voltage. For the external-drive buzzer, it depends on

1. We should give magnetic buzzer 1/2 square wave, and provide it at least 3 times the

amount of the rated consumptive current.

2. Otherwise, we give square wave to the peizo buzzer instead of 1/2 square wave,

because the half wave might cause the buzzer does not work.

Therefore, voltage control is an important factor for a peizo buzzer which is driven by

the voltage.

DC GEARED MOTOR

DC MOTOR

A DC motor is an electric motor that runs on direct current (DC) electricity.

29

DC MOTOR CONNECTIONS:

Figure shows schematically the different methods of connecting the field and

armature circuits in a DC Motor. The circular symbol represents the armature circuit,

and the squares at the side of the circle represent the brush commutator system. The

direction of the arrows indicates the direction of the magnetic fields.

BRUSHED:

The brushed DC motor generates torque directly from DC power supplied to

the motor by using internal commutation, stationary permanent magnets, and rotating

electrical magnets. It works on the principle of Lorentz force , which states that any

current carrying conductor placed within an external magnetic field experiences a

torque or force known as Lorentz force. Advantages of a brushed DC motor include

low initial cost, high reliability, and simple control of motor speed. Disadvantages are

high maintenance and low life-span for high intensity uses. Maintenance involves

regularly replacing the brushes and springs which carry the electric current, as well as

cleaning or replacing the commutator. These components are necessary for

30

transferring electrical power from outside the motor to the spinning wire windings of

the rotor inside the motor Brushed DC motor

BRUSHLESS:

Brushless DC motors use a rotating permanent magnet in the rotor, and

stationary electrical magnets on the motor housing. A motor controller converts DC to

AC. This design is simpler than that of brushed motors because it eliminates the

complication of transferring power from outside the motor to the spinning rotor.

Advantages of brushless motors include long life span, little or no maintenance, and

high efficiency. Disadvantages include high initial cost, and more complicated motor

speed controllers.

TORQUE AND SPEED OF A DC MOTOR:

The torque of an electric motor is independent of speed. It is rather a function

of flux and armature current.

CHARACTERISTICS OF DC MOTORS:

DC motors respond to load changes in different ways, depending on the

arrangement of the windings.

SHUNT WOUND MOTOR:

A shunt wound motor has a high-resistance field winding connected in parallel

with the armature. It responds to increased load by trying to maintain its speed and

this leads to an increase in armature current. This makes it unsuitable for widely-

varying loads, which may lead to overheating.31

SERIES WOUND MOTOR:

A series wound motor has a low-resistance field winding connected in series

with the armature. It responds to increased load by slowing down and this reduces the

armature current and minimizes the risk of overheating. Series wound motors were

widely used as traction motors in rail transport of every kind, but are being phased out

in favor of AC induction motors supplied through solid state inverters. The counter-

emf aids the armature resistance to limit the current through the armature. When

power is first applied to a motor, the armature does not rotate. At that instant the

counter-emf is zero and the only factor limiting the armature current is the armature

resistance. Usually the armature resistance of a motor is less than 1 Ω; therefore the

current through the armature would be very large when the power is applied.

Therefore the need arises for an additional resistance in series with the armature to

limit the current until the motor rotation can build up the counter-emf. As the motor

rotation builds up, the resistance is gradually cut out.

PERMANENT MAGNET MOTOR:

A permanent magnet DC motor is characterized by its locked rotor (stall)

torque and its no-load angular velocity (speed).

Principles of operation:

In any electric motor, operation is based on simple electromagnetism. A

current-carrying conductor generates a magnetic field; when this is then placed in an

external magnetic field, it will experience a force proportional to the current in the

conductor, and to the strength of the external magnetic field. As you are well aware of

from playing with magnets as a kid, opposite (North and South) polarities attract,

while like polarities (North and North, South and South) repel. The internal

configuration of a DC motor is designed to harness the magnetic interaction between

a current-carrying conductor and an external magnetic field to generate rotational

motion.

Let's start by looking at a simple 2-pole DC electric motor (here red represents

a magnet or winding with a "North" polarization, while green represents a magnet or

winding with a "South" polarization).

32

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator,

commutator, field magnet(s), and brushes. In most common DC motors (and all that

Beamers will see), the external magnetic field is produced by high-strength permanent

magnets. The stator is the stationary part of the motor -- this includes the motor

casing, as well as two or more permanent magnet pole pieces. The rotor (together with

the axle and attached commutator) rotates with respect to the stator. The rotor consists

of windings (generally on a core), the windings being electrically connected to the

commutator. The above diagram shows a common motor layout -- with the rotor

inside the stator (field) magnets.

The geometry of the brushes, commutator contacts, and rotor windings are

such that when power is applied, the polarities of the energized winding and the stator

magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the

stator's field magnets. As the rotor reaches alignment, the brushes move to the next

commutator contacts, and energize the next winding. Given our example two-pole

motor, the rotation reverses the direction of current through the rotor winding, leading

to a "flip" of the rotor's magnetic field, driving it to continue rotating.

In real life, though, DC motors will always have more than two poles (three is

a very common number). In particular, this avoids "dead spots" in the commutator.

You can imagine how with our example two-pole motor, if the rotor is exactly at the

middle of its rotation (perfectly aligned with the field magnets), it will get "stuck"

there. Meanwhile, with a two-pole motor, there is a moment where the commutator

shorts out the power supply (i.e., both brushes touch both commutator contacts

simultaneously). This would be bad for the power supply, waste energy, and damage

motor components as well. Yet another disadvantage of such a simple motor is that it

would exhibit a high amount of torque "ripple" (the amount of torque it could produce

is cyclic with the position of the rotor).

33

So since most small DC motors are of a three-pole design, let's tinker with the

workings of one via an interactive animation.

You'll notice a few things from this -- namely, one pole is fully energized at a

time (but two others are "partially" energized). As each brush transitions from one

commutator contact to the next, one coil's field will rapidly collapse, as the next coil's

field will rapidly charge up (this occurs within a few microsecond). We'll see more

about the effects of this later, but in the meantime you can see that this is a direct

result of the coil windings' series wiring:

The use of an iron core armature (as in the Mabuchi, above) is quite common,

and has a number of advantages. First off, the iron core provides a strong, rigid

support for the windings -- a particularly important consideration for high-torque

motors. The core also conducts heat away from the rotor windings, allowing the

motor to be driven harder than might otherwise be the case. Iron core construction is

also relatively inexpensive compared with other construction types.

But iron core construction also has several disadvantages. The iron armature

has a relatively high inertia which limits motor acceleration. This construction also

results in high winding inductances which limit brush and commutator life.

34

In small motors, an alternative design is often used which features a 'coreless'

armature winding. This design depends upon the coil wire itself for structural

integrity. As a result, the armature is hollow, and the permanent magnet can be

mounted inside the rotor coil. Coreless DC motors have much lower armature

inductance than iron-core motors of comparable size, extending brush and

commutator life.

DC motor behavior:

It gives High-speed output.This is the simplest trait to understand and treat --

most DC motors run at very high output speeds (generally thousands or tens of

thousands of RPM). While this is fine for some BEAM bots (say, photo poppers or

solar rollers), many BEAM bots (walkers, heads) require lower speeds -- you must put

gears on your DC motor's output for these applications.

Back EMF:

Just as putting voltage across a wire in a magnetic field can generate

motion, moving a wire through a magnetic field can generate voltage. This means that

as a DC motor's rotor spins, it generates voltage -- the output voltage is known as

back EMF. Because of back EMF, a spark is created at the commutator as a motor's

brushes switch from contact to contact. Meanwhile, back EMF can damage sensitive

circuits when a motor is stopped suddenly.

Noise (ripple) on power lines:

A number of things will cause a DC motor to put noise on its power lines:

commutation noise (a function of brush / commutator design & construction),

roughness in bearings (via back EMF), and gearing roughness (via back EMF, if the

motor is part of a gearmotor) are three big contributors.

Even without these avoidable factors, any electric motor will put noise on

its power lines by virtue of the fact that its current draw is not constant throughout its

motion. Going back to our example two-pole motor, its current draw will be a

function of the angle between its rotor coil and field magnets:

35

Since most small DC motors have 3 coils, the coils' current curves will overlay each

other:

Added together, this ideal motor's current will then look something like this:

Reality is a bit more complex than this, as even a high-quality motor will

display a current transient at each commutation transition. Since each coil has

inductance (by definition) and some capacitance, there will be a surge of current as

the commutator's brushes first touch a coil's contact, and another as the brushes leave

the contact (here, there's a slight spark as the coil's magnetic field collapses).

As a good example, consider an oscilloscope trace of the current through a

Mabuchi FF-030PN motor supplied with 2 V (1ms per horizontal division, 0.05mA

per vertical division):

In this case, the peak-to-peak current ripple is approximately 0.29mA, while

the average motor current is just under 31mA. So under these conditions, the motor

puts about less than 1% of current ripple onto its power lines (and as you can see from

the "clean" traces, it outputs essentially no high-frequency current noise). Note that

since this is a 3-pole motor, and each coil is energized in both directions over the

course of a rotor rotation, one revolution of the rotor will correspond to six of the

above curves (here, 6 x 2.4 ms = 0.0144 sec, corresponding to a motor rotation rate of

just fewer than 4200 RPM).

Motor power ripple can wreak havoc in Nv nets by destabilizing them

inadvertently. Fortunately, this can be mitigated by putting a small capacitor across

the motor's power lines (you'll only be able to filter out "spiky" transients this way,

though -- you'll always see curves like the ones above being imposed on your power).

On the flip side of this coin, motor power ripple can be put to good use -- as was

36

shown above, ripple frequency can be used to measure motor speed, and its

destabilizing tendencies can be used to reverse a motor without the need for discrete

"back-up" sensors

APPLICATIONS

Automobiles.

Industrial and mining applications.

Carbon monoxide monitoring and leakage detection.

37

ADVANTAGES

Content of Pollution in environment can be reduced.

Due to the implementation of this project we can maintain the co level in

atmosphere which can reduce adverse effects on environment and on human

life.

Vehicle can work smoothly and no need to pay challans to pollution control

board

Check and repair exhaust system leaks.

Long life and low cost

Ease of operation

Highly sensitive

Fit and Forget system 38

Low cost

Simple and Reliable circuits

CONCLUSION

The project “INTELLIGENT POLLUTION CONTROL SYSTEM “is

implemented successfully for automotives and industrial application for reducing and

maintaining CO level which is harmful for ecosystem and which is affordable from

small to large scale industries for maintaining pollution norms. The project is

implemented through a DC motor for symbolic representation of vehicle and user get

alert through a beep sound and if the content of co is more automatically vehicle gets

stopped with flash lights.

39

REFERENCE

1. Wikipedia

2. Embedded systems by Rajkamal

3. Magazines

4. Electronics for you

5. Electrikindia

6. www.Electronic projects.com

40