01 Electrical and Electronics Componets

8/11/2019 01 Electrical and Electronics Componets

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BUZZERS:-

A buzzer is similar in construction to a relay except for the internal wiring as shown in the

figure.

A buzzer, or sound generator, is sometimes used to warn the driver of possible safety

hazards by emitting an audio signal (such as seat belt not buckled).

The coil is supplied current through the normally closed contact points. When the voltage is

applied to the buzzer, current flows through the contact points to the coil.

When the coil is energized, the contact arm is attracted to the magnetic field. As soon as the

contact arm is pulled down the current flow to the coil is opened, and the magnetic field

disappears.

The contact arm then closes again, and the circuit to the coil is closed.

This opening and closing action occurs very rapidly and it is this movement that generatesthe vibrating signal.

RESISTORS:-

All circuits require resistance in order to operate. Resistors can be used to control current flow

and as a sensing device.

There are several types of resistors such as: fixed resistors, stepped resistors, and variable

resistors.

FIXED RESISTORS:-

Fixed resistors are usually made of carbon or oxidized metal as shown in the figure. Theseresistors have a set resistance value and are used to limit the amount of current flow in the

circuit.

The resistance value can be determined by the colour bands on the protective shell as shown in

the figure.

Usually there are four or five colour bands. If there are four bands, the first two are the digit

bands, the third is the multiplier, and the fourth is the tolerance. On a resistor with five bands,

the first three are digit bands.


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For example, if the resistor has four colour bands of yellow, black, brown and gold the

resistance value is determined as follows:

The first colour band (yellow) gives the first digit value of 4. The second colour band (black)

gives the second digit value of 0.

The digit value is now 40. Multiply this by the value of the third band. In this case brown has

a value of 10 so the resistor should have 400 ohms of resistance (40 x 10 = 400).

The last band gives the tolerance. Gold equals a tolerance range of +/- 5%.


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STEPPED RESISTORS:-

A stepped resistor has two or more fixed resistor values. The stepped resistor can have an

integral switch or have a switch wired in series.

A stepped resistor is commonly used to control electrical motor speeds as shown in the fig.

By changing the position of the switch, resistance is increased or decreased within the circuit. If

the switch is set to a low resistance, then higher current flows to the motor and the speed is

increased.

If the switch is placed in the low speed position, additional resistance is added to the circuit and

less current flows to the motor, causing it to operate at a reduced speed.


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VARIABLE RESISTOR:-

A variable resistor provides for an infinite number of resistance values within the range.

The most common types of variable resistors are rheostats and potentiometers.

A rheostat is a two terminal variable resistor used to regulate the strength of an electrical

current. One terminal is connected to the fixed end of a resistor and a second terminal is

connected to a movable contact called a wiper.

By changing the position of the wiper on the resistor, the amount of resistance can be increasedor decreased.

The most common use of the variable resistor is in the instrument panel lighting switch.


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CIRCUIT PROTECTION DEVICES

Most automotive electrical circuits

the conductors and/or the load co

To prevent damage to the compo

device. The protection device is de

The most common circuit protectio

FUSES:

There are three basic types of fus

fuses.

Glass and ceramic fuses ar

with metal caps. The metal

Blade type fuses are flat

standard, and maxi.

are protected from current flow that would exce

ponents

nents and conductors, these circuits use some f

igned to turn off the system that it protects.

n devices are :- i) Fuses ii) Fusible links iii) Circuit br

es: Glass or ceramic fuses, blade-type fuses, and

found mostly on older vehicles. Glass fuses are s

strip connects the two caps.

lastic units and are avalable in three different p

ed the capacity of

rm of protection

eakers.

bullet or cartridge

all glass cylinders

ysical sizes: mini,


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A fuse contains a metal strip that will melt when the current flowing through it exceeds

its rating.

The thickness of the metal strip determines the rating of the fuse. When the metal strip

melts, excessive current is indicated.

The most commonly used automotive fuses are rated from 4 to 30 amps.

The fuses are generally installed in a central fuse box.


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FUSIBLE LINKS:-

A fusible link is made of melt able material with a specific heat resistant insulation. When there

is an overload in the circuit, the link melts and the circuit opens.

The fusible links are usually are usually located at a main connection near the battery.

The current capacity of a fusible link is determined by its size.

A fusible link is usually four wire sizes smaller than the circuit it protects.

CIRCUIT BREAKERS


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A circuit that is susceptible to an overload on a routine basis is usually protected by a circuit

breaker.

A circuit breaker uses a bimetallic strip that reacts to excessive current as shown in the figure.

A bimetallic strip consists of two different types of metals. One strip will react more quickly to

heat than the other, causing the strip to bend in proportion to the amount of current flow.

When an overload or circuit defect occurs that causes an excessive amount of current draw, thecurrent flowing through the bimetallic strip causes it to heat.

As the strip heats, it bends and opens the contacts. Once the contacts are opened current can

no longer flow.

With no current flowing, the strip cools and closes again. If the high current cause is still in the

circuit, the breaker will open again.

The circuit breaker will continue to cycle open and close as long as the overload is in the circuit.

This type of circuit breakers is self resisting or a cycled circuit breaker.

Some circuit breakers require manually resetting by pressing a button while others must be

removed from the power to reset.


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WORKING OF ELECTROMAGNETIC GAUGES

1. FUEL GAUGE:-

Fig shows the schematic wiring diagram of a balancing coil type of fuel gauge.

It has two units a dash unit and a tank unit connected in series.

When the ignition switch is turned ON the current from the battery flows through both the

units.

The tank unit consists of a float mounted at one end of the hinged arm and a sliding contact at

the other end.

The sliding contact moves along the resistance.

The float lever moves up or down when the changes in the fuel level take place.

When the fuel level in the tank begins to empty the sliding contact moves to the left.

Thus more current flows through the left hand coil of the dash unit, and a little of it flows

through the right hand coil.

This results in the left hand coil being magnetically stronger than the right hand one.

The armature along with the pointer is moved towards the left side, thus indicating a low fuel

level in the tank.

On the other hand, when the fuel level in the tank is high, the float moves up the making thesliding contact to insert most of the resistance into the circuit.

Now most of the current that flows through the left-hand coil also flows through the right-hand

coil.

The right hand coil is relatively stronger and this causes the armature and pointer to swing to

the right, thereby indicating a high fuel level in the tank.


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2. ENGINE OIL PRESSURE GAUGE:-

This device reads the pressure of a vehicles engine lubrication system and serves as a warning

device to the driver against any likely damage to engine parts due to insufficient lubricating oil.

The oil pressure gauge can be of the Bourdon type, balancing coil type, or the thermostatic type. Fig shows the wiring diagram of the balancing coil type of oil pressure gauge.

It consists of two units namely the dash unit and the engine unit.

A variable resistance is placed in the engine unit. An increase in the oil pressure causes the

diaphragm to get pushed outwards.

This results in increase in the resistance at the engine unit, thus making the right-hand coil of

the dash unit relatively magnetically stronger than the left-hand coil.

Consequently, the armature and the pointer swing towards the right to indicate a higher oil

pressure.

3. WATER TEMPERATURE GAUGE:-

PURPOSE: - It keeps a constant check on the vehicles engine cooling system. It further alerts the driver

against overheating which can ultimately lead to piston seizure and heavy repair bills.


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Temperature gauges may be of two different types, namely, the balancing coil type and the

thermostatic type.

Fig shows the schematic wiring diagram of a balancing coil type of temperature gauge.

The operating current is supplied from the battery through the ignition switch.

In this case throughout the operation of the gauge, the current flowing through the left hand

coil is constant, whereas the current flowing through the right coil changes, depending upon the

resistance of the pellet.

When the water is cold, the battery current flows to the earth through the left coil.

This causes the pointer and the armature to swing to the cold side of the temperature scale.

When the water begins to heat up, thus heating the engine pellet, its resistance reduces,

thereby increasing the current through the right coil.

This results in a stronger magnetic field. The pointer along with the armature will move to the

hot end of the scale.

It may be remembered that the armature responds to the resultant of the two magnetic pulls.

4. SPEEDOMETER:

PURPOSE: - The purpose of the speedometer is to indicate the speed of the vehicle along with the

distance covered by the vehicle.

There are two types of speedometers namely Mechanical type and Electrical type.

The electrical speedometer operates on the principle that when an electrical generator is drivenoff the gear box output shaft it generates a voltage which is practically proportional to the

speed.

Fig shows a schematic circuit diagram of an electrical speedometer.

Small permanent magnets are embedded in a brass wheel which is rotated by a shaft at the gear

box output shaft speed.

A pick up coil is placed near it. The voltage is induced in the coil when the magnet passes it.


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These small voltage pulses are amplified by transistorized circuits and transformed in to a direct

current voltage exactly proportional to the number of impulses per second received from the

coil.

Thus the speedometer indicates the vehicle speed.

SCAN TEST FEATURES

Scan testers display data and diagnostic trouble codes (DTCs) on computer systems and

perform many other diagnostic functions.

On many vehicles, scan testers have the capability to diagnose various computer systems such

as engine, transmission, antilock brake system (ABS), suspension, and air bag.

Scan testers vary depending on the manufacturer, but many scan testers have the followingfeatures:-

1. Display Window: - It displays data and messages to the technician. Most scan testers display at

least four readings on the display at the same time.

2. Memory Cartridge: - It plugs into the scan tester. These memory cartridges are designed for

specific vehicles and electronic systems.

3. Power Cord: - Connected from the scan tester to the battery terminals or cigarette lighter

socket.

4. Adapter Cord: - Plugs into the scan tester and connects to the data link connector (DLC) on the

vehicle.

5. Serial Interface: - Optional devices, such as printer, terminal, or personal computer, may be

connected to this terminal.

6. Keypad: - Allows the technician to enter data and reply to tester messages.

Typical keys on the scan tester are: -

1. Numbered keys, digit 0 to 9

2. Horizontal or vertical arrow keys, allow the technician to move back and forward through test

modes and menus.

3. ENTER keys, to enter information into the tester.

4. EXIT MODE keys, to allow the technician to interrupt the current procedure and to back to the

previous modes.

5. F1 and F2 keys, allow the technician to perform special functions.

6. HELP key, allows the technician to obtain additional diagnostic information from the scan testersoftware.

7. YES and NO keys, allow the technician to select or reject specific procedures.

8. RECORD key, allows the technician to record data in the scan tester memory for future

reference.


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Documents

01 Electrical and Electronics Componets