01 Electrical Fault Diagnosis

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Electrical FaultElectrical Fault

DiagnosisDiagnosisMEA349AMEA349A


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Basic electrical system

1.The production of electrical energy

2.The transmission of electrical energy

3.The application of electrical energy

4.The control of electrical energy

SOURCE CONTROL LOAD

Transmission System


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arts of Electrical !ystemarts of Electrical !ystem

The source:The source: The function of the source is to pro"ide the energy for the electricalThe function of the source is to pro"ide the energy for the electricalsystem. A source may usually #e thought of as a #attery or a generator.system. A source may usually #e thought of as a #attery or a generator.

The Load:The Load: The function of the load is to a#sor# the electrical energy supplied #y theThe function of the load is to a#sor# the electrical energy supplied #y the

source. Most domestic electrical e$uipment constitutes loads. %ommon e&amplessource. Most domestic electrical e$uipment constitutes loads. %ommon e&amples

includes lamps ' heaters( all of )hich accept energy from the system.includes lamps ' heaters( all of )hich accept energy from the system.

The transmission systemThe transmission s

ystem* This conducts the energy from the source to the load.* This conducts the energy from the source to the load.

Typically the transmission system consist of insulated )ire.Typically the transmission system consist of insulated )ire.

The control apparatus:The control a

pparatus: Function is to control+ the most simple control is a s)itch.Function is to control+ the most simple control is a s)itch.

Allo)s flo) of energy. Allo)s flo) of energy.


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Resistors are de"ices )hich ma,e use of poor conductors to limit the flo) of

electricity through a circuit. -esistors are generally made of su#stances )hich

only partially conduct electricity such as car#on( special alloys and some

metal o&ides. A high "alue of resistance )ill allo) less current to flo) than a lo)

resistance.

Symbol or a Resistor Symbol or a Resistor

The unit of resistance is the ohm /pronounced o!m as in sho!0. The sym#ol

for resistance is the ree, letter omega*

A light glo#e has a resistance in the order of tens of ohms. our s,in has a

resistance in the order of millions of ohms.


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The most common resistor is the %ar#onThe most common resistor is the %ar#onresistor.resistor.

nside a car#on resistor is a ceramicnside a car#on resistor is a ceramiccore on )hich is deposited a spiralcore on )hich is deposited a spiral

car#on trac,. The trac, may ha"e #eencar#on trac,. The trac, may ha"e #eenmachined( or #urnt a)ay )ith a lasermachined( or #urnt a)ay )ith a laser

#eam#eam..

A cut5a)ay sho)ing the inside of a A cut5a)ay sho)ing the inside of a%ar#on -esistor.%ar#on -esistor.

6igh5po)er )ire5)ound resistors ha"e6igh5po)er )ire5)ound resistors ha"ea spiral of high5resistance )ire )ounda spiral of high5resistance )ire )ound

around the ceramic core.around the ceramic core.

A car#on resistor )ith the paint remo"ed A car#on resistor )ith the paint remo"edsho)ing the spiral car#on trac,.sho)ing the spiral car#on trac,.

A #ro,en resistor sho)ing the ceramic core. A #ro,en resistor sho)ing the ceramic core.

A car#on resistor )ith and )ithout the outer A car#on resistor )ith and )ithout the outerpaint.paint.

A )ire5)ound resistor A )ire5)ound resistor


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7hen current flo)s through a resistor it heats up due to the "oltage

drop across the resistor. The amount of heat a resistor can handle is

indicated #y its po!er ratin" or !atta"e. %ommon car#on

resistors ha"e a po)er rating of half a )att. 7here larger ratings are

re$uired the resistor may #e made of a spiral of 8ic,el5%hromium alloy

)hich is a#le to handle much higher currents and much more heat.

These resistors are usually termed* !ire#!ound resistors. They are

physically much larger than %ar#on and metal5film resistors.

-esistors are constructed to pro"ide predetermined resistances. Most

common resistors are guaranteed to #e )ithin : of their mar,ed

"alue. /Metal5o&ide resistors )ith a #lue #ody are guaranteed to meet

their mar,ed "alue plus( or minus 1:.0

n the early days of electronics( resistors )ere large enough to ha"etheir resistance printed directly onto the #ody of the de"ice. Modern

resistors( ho)e"er are far too small to allo) "alues to #e mar,ed and

use a colour code consisting of #ands painted onto the de"ice. Each

colour and its position represents a specific "alue.


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A typical CarbonA typical CarbonResistor rated at $%Resistor rated at $%

ToleranceTolerance

The The ToleranceTolerance #and #andindicates the accuracy of theindicates the accuracy of theresistor.resistor.

!il"er ; :!il"er ; : old ;


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-esistor %olour %hart-esistor %olour %hart

The &alues represented by each colour

are*


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Readin" Resistance 'alues:

On $% resistors (ie the ones that don)t ha&e a blue body* the irst t!o bands

represent the irst t!o di"its in the number+ The third band represents the

,multiplier, ie the number o -eros to be added ater the irst t!o numbers+ The

&alue is in )ohms)+

eg1eg1

TheThe di"itsdi"its areare redred(( redred 5 therefore* 2( 25 therefore* 2( 2TheThe multiplier multiplier isis oran"eoran"e 5 therefore* >>>5 therefore* >>>/ie three ?eros0/ie three ?eros0The "alue is therefore* 2 2 > > > ohms( orThe "alue is therefore* 2 2 > > > ohms( or22 thousand ohms( or 22,ohms( or 22 , .22 thousand ohms( or 22,ohms( or 22 , .

eg2eg2

TheThe di"itsdi"its areare bro!nbro!n(( blac.blac. 5 therefore* 1( >5 therefore* 1( > TheThe multiplier multiplier isis blac.blac. 5 therefore*5 therefore*

n 8il /ie no ?eros0 n 8il /ie no ?eros0

TheThe &alue&alue is therefore* 1> ohms( 1> .is therefore* 1> ohms( 1> . The common mista,e as 1>> .The common mista,e as 1>> .The last #and says there are @E- ?eros aThe last #and says there are @E- ?eros a

f after thef after the first #lac,. is to interpret thisfirst #lac,. is to interpret this

c com#ination c com#ination


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/% Tolerance Resistors

0i"h accuracy resistors are made usin" a metal#o1ide ilm2 rather than Carbon+ These

resistors ha&e a blue body and our colour bands instead o three+ The same colour

code system applies2 but there are three )di"it) bands and one )multiplier) band+

n metal5o&ide resistors then metal5o&ide resistors the ToleranceTolerance #ands are*#ands are*Bro)n ;


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CAPACITORS

In its simplest form, a capacitorIn its simplest form, a capacitor

consists of anconsists of an insulatorinsulator

sandwiched between twosandwiched between twoconductorsconductors. The insulator is. The insulator is

called a "called a "dielectricdielectric" and may" and may

consist of almost any insulatingconsist of almost any insulating

material ranging from paper,material ranging from paper,

glass, ceramic, air, oil, plasticglass, ceramic, air, oil, plasticand so on.and so on.

Often the 'sandwich' is rolledOften the 'sandwich' is rolled

into a cylindrical shape to saveinto a cylindrical shape to save

space.space.

E1ploded &ie! o a typicalE1ploded &ie! o a typical

capacitor # An insulatorcapacitor # An insulatorbet!een t!o conductors+bet!een t!o conductors+


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7hen a capacitor /also called a condenser 0 is connected into an

electrical circuit and a "oltage is applied( electrons flo) onto the metal

plates. f the circuit is then disconnected the char"e )ill remain on the

plates. A capacitor therefore acts as a stora"e de&ice for electricity. Thecapacitors used for tuning in radio applications( often ha"e mo"ea#le

plates( #ut in #y far the maCority of applications( the positions and si?es of

the plates and dielectric are fi&ed. /6ence the capacitance remains

constant.0

Symbol or a Capacitor Symbol or a Capacitor

The unit of capacitance is the 8arad. /After Faraday0 The sym#ol is the ree,

letter mu or* 0


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ntil "ery recently( it )ould #e true to say that a one5farad capacitor

)ould #e the si?e of a dinner plate. The farad is a "ery large unit. The

maCority of capacitors in general use ha"e "alues in the range of* micro#

arads( nano#arads( or pico#arads

((One arad 9 one million micro#arads 9 one thousand million nano arads 9 oneOne arad 9 one million micro#arads 9 one thousand million nano arads 9 onemillion million pico arads+*million million pico arads+*

arge capacity capacitors are used in domestic appliances such assome "ideo recorders as an emergency memory #ac,5up po)er supply(

rather than using #atteries. Typically( these capacitors may ha"e "alues

of fi"e or si& farads at 3 "olts. This storage feature of capacitors ma,es

them useful in A% to D% po)er supplies )here they are used to help

smooth the resulting D% output.


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The ,ey to understanding the other main use of capacitors in circuits is that they are

#asically insulators.

f a #attery is connected to a capacitor( electrons )ill flo) from the #attery onto one of

the plates and from the other plate into the #attery. This flo) of current )ill continue until

the charge on each plate is at its ma&imum. /As determined #y the construction of the

capacitor.0For the #rief time this process is ta,ing place( there appears to #e a complete circuit. f a

glo#e )ere connected into this circuit( it )ould glo) during the time current )as flo)ing

and charging the plates.

7hen the s)itch is closed electrons flo) into the7hen the s)itch is closed electrons flo) into thecapacitor. 7hile the capacitor is charging the glo#e )illcapacitor. 7hile the capacitor is charging the glo#e )illlight up.light up.

f the #attery is remo"ed and the s)itch closed( electronsf the #attery is remo"ed and the s)itch closed( electronsflo) out of the capacitor. The glo#e lights up.flo) out of the capacitor. The glo#e lights up.

%onsider then( if alternatin" current /A%0 is applied to the capacitor( the plates )ill #econtinually charging and discharging as current flo)s into and out of the plates. A glo#e

connected into the circuit )ill no) remain alight for as long as the "arying "oltage is

applied.

A capacitor )ill therefore conduct chan"in" current( #ut #loc, D.%. /t is important to

appreciate that the "oltage need not necessarily alternate from positi"e to negati"e to #e

passed+ a changing d.c. current )ill pass through a capacitor.0


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ELECTR5CAL C0ARACTER5ST5CS O8 CAAC5TORS

As outlined pre"iously( one use of capacitors is )here the

designer )ishes to pass changing "oltage / the si"nal0

)hile #loc,ing un)anted D% effects. The choice of

capacitor depends upon t)o factors 5 the signal "oltage

and its fre$uency. /n some cases( current is also

significant.0

f the applied "oltage e&ceeds the rating of the capacitor(

current may punch through the dielectric from one plate

to the other. Ma&imum "oltage rating is usually mar,ed on

the capacitor in some )ay.

The si?e of the plates and the thic,ness of the dielectric

determines the efficiency )ith )hich the capacitor )ill

pass a particular signal. A small2 thin capacitor is moreeffecti"e for hi"her re;uency signal than one )ith large

plates and thic, dielectric.

hysical construction and the type of materials used )ill

also ha"e an effect on the re;uency response o

capacitors.

nce the general type of capacitor has #een chosen

/refer to the follo)ing ta#le0( the designer must select the

capacitance needed to pass the specific signal. As a

general guide( if audio signals are in"ol"ed /se"eral

thousand 6?0( typical "alues )ould #e tens of micro5

farads( )hile radio fre$uency signals )ould necessitate

the use of pico( or nano "alue.

n reality( consideration must #e gi"en to the effects of

other components( #ut the general rule applies.

%AA%T-!5 T%A EE%T-%A%6A-A%TE-!T%!*

CapacitorCapacitortypetype > "olts1>> "olts

typicaltypical lo) tolo) to

mediummedium

tantalumtantalumup to >"up to >"

typicaltypicallo)lo)

electrolyticelectrolyticup to 1>>"up to 1>>"

typicaltypicallo)lo)


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CAAC5TOR S

The capacitance of capacitors may #e mar,ed in one of se"eral )ays.

7here there is sufficient room on the #ody of the de"ice a num#er and the units

)ill #e printed e.g. 1>>uF 2 G7( )hich indicates that this capacitor has a

capacitance of 1>> micro5farads and a #rea,do)n "oltage of 2 "olts.

/appro&imately0

!maller capacitors( such as greencaps use a numerical system )here the first

place represents the first digit( the second place+ the second digit and the thirdplace is the num#er of ?eros. /the multiplier0 The capacitance so indicated is in

picofarads

1>4 H ; 1>>(>>>pF or >.1uF

%olour codes follo) a similar pattern to that used for resistors( #ut they tend to

#ecome rather confusing at times. A good set of data sheets should #e consulted

)hen decoding is needed.

D5ODES


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D5ODES

Diodes are the simplest of the solid5state de"ices. !olid state #asically means an

electronic component or de"ice that is composed chiefly or e&clusi"ely of solid

materials( usually semi conducting. A solid5state has no mo"ing parts. Diodes consist

of a piece of 5type material fused to a piece of 85type material. The most common

forms of diodes are constructed from !ilicon. ermanium is less sta#le at hightemperatures than !ilicon. ts use is generally reser"ed for those special applications

)here a lo) for)ard #ias is essential. ermanium is less sta#le at high temperatures

than !ilicon.

!ym#ol for a Diode

A diode )ill only conduct in one direction( )ith electrons flo)ing from the 85type end to

the 5type end./ie from the %athode to the Anode0

f a "oltage is applied )hich re"erse #iases the Cunction( the depletion layer )ill )idenuntil a point is reached )here the "oltage e&ceeds the #rea,do)n "oltage of the diode

and large currents flo)+ destroying the de"ice. ne type of diode( the ?ener( actually

ma,es use of #rea,do)n "oltage in an interesting )ay. This )ill #e discussed later

There are many different forms of diodes( from simple point5contact signal diodes to

multi5coloured light emitting diodes. A fe) of the more common "arieties )ill #e

discussed.


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Si"nal Diodes

!ignal diodes are physically small de"ices usually used )here small

currents( high "oltages and high fre$uencies are in"ol"ed. The si?e of

the Cunction has an effect on the signal capa#ilities of the diode. Asmall Cunction offers less resistance to high fre$uencies than does a

)ide thic, Cunction. The name comes from the fact that these diodes

are suita#le for use in radio detectors to isolate the radio signal.

!ignal diodes are "ery small and often glass encapsulated( )ith a red

or #lac, #and on one end. /The glass is sometimes painted o"er to

reduce un)anted photo5"oltaic effects.0


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o!er Diodes

7here larger currents are in"ol"ed( a larger Cunction is needed to dissipate the heat

generated. A small Cunction )ould #e in danger of literally melting )ith currents in

e&cess of a fe) hundred milli5amps.

!ince the po)er diode has a large Cunction( it is not suited to high fre$uency applications.

/6igh fre$uency( high current diodes are a"aila#le( #ut the cost is su#stantial.0

ne ad"antage of the larger Cunction is its a#ility to )ithstand higher "oltages )ithout

sustaining damage. 7hile a signal diode may only #e a#le to ta,e 3> to > "olts re"erse

potential( it is $uite common to find po)er diodes rated up to se"eral thousand "oltsma&imum re"erse #ias. /Termed ea, n"erse Goltage( or G.0

o)er diodes are a#le to pass large loads "arying from the 184>>I series rated at 1

amp up to industrial diodes capa#le of carrying 1>>Js of amps

These diodes come in a "ariety of encapsulations( the most common #eing a #lac,

cylinder of plastic a#out 3mm long )ith a )hite #and indicating the cathode /negati"e0

end. arge5current de"ices are often encased in metal to pro"ide efficient heat transfer.

Li"ht Emittin" Diodes


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Li"ht Emittin" Diodes

ight emitting diodes /EDs0 are among the most )idely used of all types of diodes. %olours

a"aila#le range from red( orange( yello)( green and #lue. !i?es are 3mm( or mm. t is also

possi#le to purchase rectangular EDs and special5purpose EDs( for e&ample EDs that

ha"e #een moulded to represent a small dot. Most EDs ha"e a couloured lens( #ut it is

possi#le to #uy )ater5clear EDs that ha"e no colouring in the plastic lens. EDs are also

a"aila#le in different intensities ranging up to se"eral candle5po)er.

The most common (and cheapest* LED is the $mm red LED+

EDs are also a"aila#le in pac,ages arranged to produce letters and numerals. The price

and a"aila#ility of these pac,ages depends to a large e&tent upon current industrial

re$uirements.8umerals are produced #y arranging EDs in a se"en5segment arrangement as indicated

#elo). ntegrated circuits /%s0 are a"aila#le for dri"ing displays directly. /The 4>2K % for

e&ample( )ill ta,e pulses( count them and display the count on a se"en5segment display( all

for a fe) dollars0

A red ED and a !e"en5segment Display.


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As )ith all diodes( orientation of EDs is critical. f you connect the legs the

)rong )ay around it )ill not conduct. The follo)ing diagram should pro"ide

a useful guide. This property is "ery useful )hen using a diode to pro"ideprotection against "oltage re"ersal 5 also called* idiot5proofing. f a diode is

#uilt into the po)er section the rest of the circuit )ill #e protected in the

e"ent of some#ody connecting the po)er supply the )rong )ay around.

?ener Diodes


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?ener Diodes

f a re"erse #ias is applied to a diode it )ill resist conduction until a point is reached

)here current is forced to flo). This "oltage is called the ea, n"erse Goltage( or+

#rea,do)n "oltage.

nder normal circumstances( the diode )ould #e destroyed.

t )as disco"ered that precise production techni$ues could produce a diode )ith apredetermined #rea,do)n "oltage )hich )as less li,ely to #e damaged #y re"erse

current flo). The effect is called the ?ener effect after %larence Mel"in @ener. This

type of diode is called a @ener Diode.

The result is de"ice )hich maintains a constant "oltage across its ends regardless of

the input "oltage.

@eners are a"aila#le in a "ariety of ratings( the most economical #eing a one )att"ersion.

t must #e remem#ered that @eners are used in -EGE-!E mode( i.e. the anode

connects to the negati"e supply.

NOTE: Zener diodes are used in REVERSE mode.

The anode connects to negative. ?ener Diodes are used in re&erse+


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Transistors

A transistor may be thought of asan electronic tap able tocontrol a large flow of electronswith only small variations ofthe 'handle'.

The 'handle' in the case of atransistor is called the "base".The in and out 'pipes' are calledthe "emitter" and the"collector".

Voltage changes at the base of thetransistor result in changes tothe flow of electricity throughthe transistor.

A transistor can be thou"ht o

as a )tap)+


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Symbol or a Transistor

When we think of a water tap we know that large amounts ofwater can be controlled by very small movements of the spigot

(the tap handle). It is useful to think of electricity owing around acircuit in the same way we think of water owing in pipes. With anelectronic 'tap' the ow of electricity is controlled by varying thevoltage between the emitter and base of the transistor. The main flo)is a path #et)een the emitter and the collector.

Transistors are used in t)o #asic )ays+

1. As an electronic s)itch. ie they are either fully 8( or fully FF. /eg to

s)itch a relay0

2. To pro"ide amplification of a small changing "oltage / a signal0 present

at the Base. /eg in an audio amplifier0

as ng rans s ors:


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as ng rans s ors:To eep the transistor operating within this useful range, resistors are used to

establish a predetermined potential difference between emitter and base and base and

collector. These resistors are called 'bias' resistors. !ometimes a resistor is also used

in the base circuit to limit the flow of current into the base. There are a variety of

ways to provide the correct 'bias' to a transistor, one of the most common is presented below

Resistors R/ and R@ orm a )&olta"e di&ider) !hichestablishes correct bias and ensures a )linear) response+

A Transistor usin" the small current a&ailable rom

a computer rinter ort to control a Relay


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Transistors come in all shapes and sies. !enerally theyhave three 'legs'" but not all three#legged components

are transistors. The sie of a transistor is usuallydetermined by the amount of current they are re$uiredto handle. %arge#current transistors are physically largeand often have enhanced cooling features such a metalcase.


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Transormers

A transformer is a de"ice for stepping5up( or stepping5do)n( the "oltage of

an alternating electric signal. 7ithout efficient transformers( the transmission

and distri#ution of ac electric po)er o"er long distances )ould #e

impossi#le.

Three phase transformer forpowering a suburb.


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There are two circuits& the primary circuit" and the secondary circuit. There is no direct electrical connection between the two circuits" buteach circuit contains a coil which links it inductively to the other circuit.In real transformers" the two coils are wound onto the same iron core.

The purpose of the iron core is to channel the magnetic u generatedby the current owing around the primary coil" so that as much of it aspossible also links the secondary coil. The common magnetic u linkingthe two coils is conventionally denoted in circuit diagrams by a numberof parallel straight lines drawn between the coils (see above).

The gure below shows the circuit diagram of a typicaltransformer.

#hereas an electric field flu$ between two conductors allows for an accumulation of free


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#hereas an electric field flu$ between two conductors allows for an accumulation of free

electron charge within those conductors, an electromagnetic field flu$ allows for a certain

"inertia" to accumulate in the flow of electrons through the conductor producing the field.

Inductors are components designed to tae advantage of this phenomenon by shaping the

length of conductive wire in the form of a coil. This shape creates a stronger magnetic

field than what would be produced by a straight wire. !ome inductors are formed withwire wound in a self%supporting coil. Others wrap the wire around a solid core material of

some type. !ometimes the core of an inductor will be straight, and other times it will be

&oined in a loop s(uare, rectangular, or circular) to fully contain the magnetic flu$. These

design options all have effect on the performance and characteristics of inductors.

The schematic symbol for an inductor, lie the capacitor, is (uite simple, being little more

than a coil symbol representing the coiled wire. Although a simple coil shape is thegeneric symbol for any inductor, inductors with cores are sometimes distinguished by the

addition of parallel lines to the a$is of the coil. A newer version of the inductor symbol

dispenses with the coil shape in favour of several "humps" in a row


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As the electric current produces a concentrated magnetic field around the coil( this field

flu& e$uates to a storage of energy representing the ,inetic motion of the electrons

through the coil. The more current in the coil( the stronger the magnetic field )ill #e(

and the more energy the inductor )ill store.

Because inductors store the ,inetic energy of mo"ing electrons in the form of a

magnetic field( they #eha"e $uite differently than resistors /)hich simply dissipate

energy in the form of heat0 in a circuit. Energy storage in an inductor is a function of

the amount of current through it. An inductors a#ility to store energy as a function ofcurrent results in a tendency to try to maintain current at a constant le"el. n other

)ords( inductors tend to resist changes in current. 7hen current through an inductor is

increased or decreased( the inductor resists the change #y producing a "oltage

#et)een its leads in opposing polarity to the change.


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Battery construction

The )ord battery simply means a group of similar components. n military "oca#ulary( a #attery refers to a

cluster of guns. n electricity( a #attery is a set of "oltaic cells designed to pro"ide greater "oltage and=or

current than is possi#le )ith one cell alone.

The sym#ol for a cell is "ery simple( consisting of one long line and one short line( parallel to each other( )ithconnecting )ires*

The sym#ol for a #attery is nothing more than a couple of cell sym#ols stac,ed in series*

Goltage produced #y any particular ,ind of cell is determined strictly #y the chemistry of that cell type. The

si?e of the cell is irrele"ant to its "oltage. To o#tain greater "oltage than the output of a single cell( multiple

cells must #e connected in series. The total "oltage of a #attery is the sum of all cell "oltages. A typical

automoti"e lead5acid #attery has si& cells( for a nominal "oltage output of K & 2.2 or 13.2 "olts*


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Solenoid

A long straight coil of wire can be used to generate a nearly uniform magnetic field

similar to that of a bar magnet. !uch coils, called solenoids, have an enormous number

of practical applications. The field can be greatly strengthened by the addition of an

iron core. !uch cores are typical in electromagnets.

S l id

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html


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Solenoids

!ince the magnetic field is created #y mo"ing electrons )e could argue that the more

electrons are mo"ing( the stronger the magnetic field )ould #e. A gi"en length of )ire

contains a certain num#er of electrons. T)ice that length )ill contain t)ice as many

electrons. f a solenoid is made )ith more turns or )raps of )ire( then it must createa stronger magnetic field.

This solenoid has onlythree turns or wraps ofwire around it. Itsmagnetic eld is notvery strong.

This solenoid has * turns of wire aroundit. If all else is constant" the magneticeld should be twice as strong since ithas twice as many turns.

L i


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Lo"ic "ates

Digital systems are said to #e constructed #y using three #asic logic gates.

These gates are the A8D gate( - gate and 8T gate. There also e&ists other

logical gates( li,e the 8A8D( and the E- gates. 7e )ill only #e loo,ing at the

first three gates. The #asic operations are descri#ed #elo).

AND "ate

The A8D gate is an electronic circuit that gi"es a high output /10 only if all its

inputs are high. A dot /.0 is used to sho) the A8D operation. Bear in mind that

this dot is usually omitted( as sho)n at the output a#o"e.


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The - gate is an electronic circuit that gi"es a high output if one or more of its inputs

are high. A plus /


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This is a *OT%A*+ circuit which is e(ual to an A*+ circuit followed by a *OT circuit. The

outputs of all *A*+ gates are high if any of the inputs are low.

NAND "ate

This is a *OT%O circuit which is e(ual to an O circuit followed by a *OT circuit. The

outputs of all *O gates are low if any of the inputs are high.

NOR "ate

The 'Eclusi!e"OR ' gate is a circuit which will give a high output if eit#er$ but not bot#,

of its two inputs are high. An encircled plus sign ) is used to show the -O operation.

EOR OR ate


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Electric Starter


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%o you #a!e many &uestions'

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01 Electrical Fault Diagnosis

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