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elec01 esential electrical concept.pdf

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ELEC01 ESENTIAL ELECTRICAL CONCEPT
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Electrical Circuit Diagnosis - Course 623 1-1 Modernvehiclesincorporatemanyelectricalandelectroniccomponents andsystems: w Audio w Lights w Navigation w Enginecontrol w Transmissioncontrol w Brakingandtractioncontrol Youneedtoknowessentialelectricalconceptstoeffectively troubleshoottheseandotherelectricalcircuits. Electricalandelectronicsystemtroubleshootingcanbestraightforward if 0 w Youknowwhattolookfor. w Youknowhowtoselectandusetheappropriatetoolsandtest equipment. Withtheknowledgeandtechniquesyouwilllearninthiscourse,you willbeableto 0 w Diagnoseandrepairelectricalandelectronicproblemscorrectlyon thefirstattempt. w Reducediagnosticandrepairtime. w Increasecustomersatisfaction. Section 1 Essential Electrical Concepts IntroductionSection 1 1-2 TOYOTA Technical Training Differentmetersareusedtomeasurevoltage,current,andresistance: w Voltmeter-tomeasurevoltage w Ammeter-tomeasurecurrent w Ohmmeter-tomeasureresistance Thesethreemeteringfunctionsarecombinedintoasingletestercalled amultimeter.“Nearlyallautomotivetechniciansusemultimeters. Amultimeterisoftencalledavolt-ohmmeter,“eventhoughmost multimetersalsomeasureamperes(current). Amultimetercanbeoneoftwotypes: 1. Analog-displayusesaneedletopointtoameasuredvalueonascale. 2. Digital-displayshowsmeasuredvalueinactualnumbers(digits). Metering Functions Three metering functions are combined in a typical digital multimeter. Fig. 1-01 TL623f100c MetersEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-3 Analogmultimeters 0 w Useamechanicalmovementtodriveapointer. w Displayameasuredvaluewherethepointerintersectsacalibrated scale. w Arenotsuitableformeasurementsincircuitswithsensitive electroniccomponents(suchasECUs). w Aremoresusceptibletodamagefrommechanicalshockthanare digitalmultimeters. Typical Analog Multimeter Analog meters use a mechanical movement and are not suitable for measurements in circuits with sensitive electronic components. Fig. 1-02 TL623f102 Analog MultimetersSection 1 1-4 TOYOTA Technical Training Digitalmultimeters 0 w Useadigitaldisplay. w Displayameasuredvalueinactualnumbers. w Aresuitableformeasurementsincircuitswithsensitiveelectronic components(suchasECUs). w Arelesssusceptibletodamagefrommechanicalshockthanare analogmultimeters. w Havealongerbatterylife. w Haveahigherinternalresistance. Typical Digital Multimeter Digital multimeters display the actual measured value and are suitable for measurements in circuits with sensitive electronic components. Fig. 1-03 TL623f103c Digital MultimetersEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-5 Themaincomponentsfoundonthefrontpanelofatypicaldigital multimeter(DMM)are 0 w Digitaldisplay w Rangeselector w Modeselector w Inputjacks DMM Components This figure shows the main components of a typical digital multimeter. Fig. 1-04 TL623f104c DMM ComponentsSection 1 1-6 TOYOTA Technical Training Usethemodeselectortosetthemeterforthetypeoftesttobe performed.ThesearethemodesavailableonaFluke87DMM: w Off- Turnsthemeteroff.Turningthemodeselectortoanyother settingturnsthemeteron. w VoltsAC- Usetomeasurevoltageinalternatingcurrent(AC) circuits. w VoltsDC- Usetomeasurevoltageindirectcurrent(DC)circuits. w MillivoltsDC(mV)DC- Usetomeasureverylowvoltagein directcurrent(DC)circuits. w Resistance/Continuity(ohms)- Usetomeasureresistanceand checkcontinuity. w DiodeCheck- Usetochecktheoperationofadiode(metersends asmallcurrentthroughthediode). w AmpsorMilliampsAC/DC- Usetomeasurecurrentinacircuit. w Microamps(AC/DC)- Usetomeasureverysmallcurrentina circuit. DMM Mode Selector The mode selector knob lets you set the meter for the type of test you want to perform. Fig. 1-05 TL623f105 DMM Mode SelectorEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-7 DMMsdisplayinformationthatmustbeproperlyinterpretedtogetthe correctmeasuredvalue. Interpreting DMM Displays The digital display gives a direct readout in actual numbers. However, you still must properly interpret the display to get the correct measurement value. Fig. 1-06 TL623f106 Voltagetype- TheDMMshowsthevoltagetype(ACorDC)inthe upperrighthandcornerofthedisplay. Measuredvalue- Thelargedigitsinthecenterofthedisplay representthemeasuredvalue.Typically,thetotalvaluewillcontain fourorfivedigitswithadecimalpoint. Units- Totherightofthemeasuredvaluenumber,thedisplayshows lettersthatrepresentunits: V volts A amperes ohms Range- TheDMMdisplaysthemeasurementrangeinthelowerright handcornerofthedisplay,justtotherightofthebargraph. DMM DisplaySection 1 1-8 TOYOTA Technical Training Unitmodifiers- Thelettersm,k, m ,andMmodifyunitvalues: Volts- mV millivolts voltsx0.001 kV kilovolts voltsx1,000 Amperes- mA milliamps ampsx0.001 m A microamps ampsx0.000001 Automotivetechniciansrarelyusereadingsatthemicroamplevel. Ohms- ohms k kilo-ohms ohmsx1,000 M megohms ohmsx1,000,000 DMM Over-Limit Display The “O.L” or “over-limit” display appears whenever the test produces a value that exceeds the selected range. For resistance, that typically indicates an open circuit. Fig. 1-07 TL623f107 Over-LimitMeasurement- MostDMMsdisplayanover-limitsign whenthemeterismeasuringvoltageorcurrentthatexceedstheselected oravailablerange. NOTEEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-9 ManyDMMsofferafeaturecalledauto-ranging.“Meterswiththis featureallowyoutodisableitwhenyouwanttoselectrangesmanually. Whenthemeterissettoauto-range,itautomaticallyselectstherange mostappropriateforthemeasurementbeingperformed. Auto-rangingisconvenientformakingmostmeasurements.Itis especiallyhelpfulwhenyoudonotknowwhatvaluetoexpect.A resistancemeasurementprovidesagoodexample. AtypicalDMMhastheserangesavailableforresistance measurements: w 400 w 4k./40k /400k w 4M./40M IftheDMMisconnectedtoacomponentwithaninternalresistanceof about700ohms,themetercanautomaticallyselectthe4k.range.Without auto-ranging,youmightscanthroughseveralrangesbeforedetermining thatthe4k rangeismostappropriateforthismeasurement. DMM Auto- Ranging Digital multimeters with auto-ranging will automatically select the appropriate scale for a test measurement. Fig. 1-08 TL623f108 DMM Auto-Ranging EXAMPLESection 1 1-10 TOYOTA Technical Training ThetypicalDMMhastwotestleadsandfourinputjacks.Theleads pluginasfollows: w BLACK -alwaysplugsintotheCOMinputjack. w RED -plugsintooneofthethreeremainingjacks,dependingon whatmeasurementisbeingperformed. -V / /diodeinputformeasuringresistance,conductance,and capacitance,aswellascheckingdiodes(Voltage). - Ainputformeasuringcurrentupto10amps. - m A/mAinputformeasuringcurrentupto400mA. DMM Input Jacks The meter leads must be plugged into the proper input jack for different tests (voltage and resistance or two ranges of current). Fig. 1-09 TL623f109c DMM Test Leads and Input JacksEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-11 Voltageistheelectromotiveforcebetweentwopointsinacircuit. WhenyouplacetheprobesofaDMMontheterminalsofabattery,you aremeasuringtheelectromotiveforce,orvoltage,betweenthepositive andnegativebatteryplates. Overview This meter is connected to measure battery voltage. Fig. 1-10 TL623f110c Voltage EXAMPLESection 1 1-12 TOYOTA Technical Training Applicationsofvoltage- Techniciansareconcernedwithvoltagein differentapplications: w Sourcevoltage w Availablevoltage w Voltagedrop Sourcevoltage- thebatterysuppliessourcevoltageinmost automotiveelectricalsystems. Measuringvoltage- usetheDMMtomeasurevoltage.Notethat voltagemeasurementsaremadebyplacingthevoltageleadsina parallelcircuittothecircuityouaretesting.(Parallelcircuitsare coveredinSection2.) Availablevoltage- isthevoltageinacircuitavailabletooperatethe load. Voltagedrop- mostpartsofanelectricalcircuitofferssome resistancetocurrent.Everyelementthathasresistancecausesa voltagedrop.Voltagedropincreasesasresistanceincreases.Essential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-13 Measuring Voltage The meter leads in this figure show three different ways to measure voltage. Fig. 1-11 TL623f111c Youcanmeasurevoltage 0 w Betweenanytwopointsinacircuit w Betweenanypointinacircuitandground w Acrossanycomponentinthecircuit - Switches - Relaycontactsandcoils - Connectors - Wires - CablesSection 1 1-14 TOYOTA Technical Training Available Voltage The meter probes are placed to test the available voltage at the switch. Fig. 1-12 TL623f112cEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-15 Measureavailablevoltageusingadigitalmultimeterwiththesesteps: 1. SetthemodeselectorswitchtoVoltsDC. 2. SelecttheAuto-Rangefunctionormanuallysettherange. - Becausethebatterysuppliesavailablevoltageinautomotive circuits,youwilltypicallymeasurevoltagesbetweenzeroand12 to14volts. - ForFlukeSeries80DMMs,settherangeto40. - ForotherDMMs,settherangetothevalueclosesttoandhigher than12volts. 3. Connectthevoltmeterleadsinparallelwiththecircuitelementto betested. - Redleadclosesttothebattery(connectfirst). - Blackleadtoagoodground. 4. ReadmeasurementonDMMdisplay. - Notepolarity. - Correctlyapplyunits. ThemeterleadsaremostlikelyreversediftheDMMdisplayindicates negativepolarity.Itcouldalsomeanthereisafaultinthecircuit. Available Voltage NOTESection 1 1-16 TOYOTA Technical Training Voltage Drop Voltage drop indicates the voltage being used in that section of the circuit. Fig. 1-13 TL623f113c Voltagedropisoneofthemostusefultestsyoucanperform.Avoltage droptestisolatesvoltageusedintheportionofthecircuitbeingtested. Avoltagedroptestisdoneasfollows: 1. Placethepositiveleadinthemostpositivesectionofthecircuityou aretesting. 2. Placethegroundleadonthemostnegativesectionofthecircuit youaretesting. 3. Operatethecircuitwiththemeterleadsinplaceandnotethereading. Voltage DropEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-17 Typicalvoltagedropsareasfollows: w Acrossaswitch,relaycontactsorconnector:Lessthan200mV (12.4V). Thesumofallvoltagedropsinacircuitequalsthesourcevoltage.A voltagedropthatexceedsnormallimitsindicatesexcessiveresistance (anunwantedload)inthatportionofthecircuit. Avoltagedroptestcanquicklyisolateexcessiveresistanceinacircuit thatmaynotbedetectedusingaresistancetest.TheOhmmeteronly passesasmallcurrentthroughtheportionofthecircuityouare testing.Avoltagedroptestisdonewithcircuitoperatingatnormal currentlevels.Aloosepininaconnectororadamagedwiremayshow continuitywiththeOhmmeterbutunderloadshowavoltagedropdue totheincreasedresistanceduringnormalcurrentlevels.Section 1 1-18 TOYOTA Technical Training Converting Voltage Values To convert volts to millivolts (and vice versa) just move the decimal point three places. Fig. 1-14 TL623f114c ConvertingVoltageValues - Automotivevoltagevaluesvaryfrom around14voltstoverysmallvaluesunder50mV. HybridvehiclessuchasthePriususecircuitswithhighvoltageand current(over100volts).Followallsafetyprecautionsandservice procedureswhenworkingonhighvoltagecircuits. Valuesunder1voltareoftenexpressedasmillivolts.1voltisequalto 1,000millivolts. Convertthevaluesasfollows: w Voltstomillivolts,movethedecimalpoint3placestotheright. (example:1.34V=1,340mV) w millivoltstovolts,movethedecimalpoint3placestotheleft. (example:289mV=.289V) Practice- Convertthefollowingvoltagevalues: 50mV= V 3,233mV= V 9.48V= mV .27V= mV CAUTIONEssential Electrical Concepts Electrical Circuit Diagnosis - Course 623 1-19 Currentismeasuredinamperesoramps.“Currentissometimescalled amperage. Currentispresentinacircuitwhen 0 w Thereissufficientavailablevoltage. w Thereisacontinuouspathfromthesource,throughtheload,to ground. Youwillnotusecurrentmeasurementsasoftenasvoltage measurements.Mostdiagnosticspecificationsforautomotivecircuits specifyvoltageorresistance. Youwillmeasurecurrenttodiagnose 0 w Faultsinstartingandchargingsystems. w Parasiticloadfaults. Aparasiticloadisanunwantedloadthatdrawscurrentwhenthe ignitionswitchisturnedtoOFF.Thisproblemistypicallyreportedas batterydrainswhilevehicleisparkedovernight.“ Measuring Current A convenient place to measure current is at the fuse holder. When you remove the fuse to measure current, always use a fused jumper wire or leads as shown. Fig. 1-15 TL623f115c CurrentSection 1 1-20 TOYOTA Technical Training DMMconnections- ADMMisconnecteddifferentlyformeasuring currentthanitisformeasuringvoltage: w Voltage-meterconnectedinparallelwithcircuitelement. w Current-meterconnectedinserieswithcircuit(currentactually flowsthroughthemeter). Maximumcurrentcapacity- Itisimportanttoobservethe maximumcurrentcapacityoftheDMMyouareusing.Todetermine themaximumcurrentcapacity: w ReadtheratingprintednexttotheDMMinputjacks. w Checktheratingofthemeter’sfuse(maximumcurrentcapacityis typicallythesameasthefuserating). Useonlyfusesofthecorrecttypeandratingforeachmeter. Substitutinganincorrectfusecouldcausedamagetothemeter. Ifyoususpectthatameasurementwillhaveacurrenthigherthanthe meter’smaximumrating,useanoptionalinductivepickup.Some specifictesters,suchastheSunVATseries,havebuiltinammeters withhighcurrentratingsfortestingstartingandchargingsystems. MeasurecurrentwithaDMMusingthesesteps: 1. Turnthecircuittobetestedoff. - MakesureleadsareincorrectjacksonDMM. 2. SettheDMMmodeselectortotheappropriatecurrentfunction (typicallyampsormilliamps). 3. SelecttheAuto-rangefunctionormanuallyselecttherangeforthe expectedcurrentvalue. 4. Openthecircuitatapointwherethemetercanbeinsertedin series. - Afuseholdermakesaconvenientpointtoopenacircu
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