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elec06 electrical signal.pdf

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ELEC06 ELECTRICAL SIGNAL
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Electrical Circuit Diagnosis - Course 623 6-1 Oscilloscope An oscilloscope displays voltage changes over time. Use an oscilloscope to view analog and digital signals when required during circuit diagnosis. Fig. 6-01 TL623f600c Anunderstandingofdigitalandanalogsignalswillhelpyouchoose appropriatetestequipmentandtroubleshooteffectively.Automotive circuitsusetwotypesofsignals: w INPUT-providesinformationaboutoperatingconditions (switches,sensors) w OUTPUT-causesanelectricalorelectronicdevicetooperate (lamps,LEDs,relays,motors) Inputandoutputsignalscanbeeitherdigitaloranalog,dependingon theapplication.ElectronicControlUnits(ECUs)typicallyreceive, process,andgeneratebothanaloganddigitalsignals. Section 6 Introduction to Electronic Signals Input and Output SignalsSection 6 6-2 TOYOTA Technical Training Asignalthatrepresentsacontinuouslyvariablevoltageisananalog signal. Variableresistors- Athrottlepositionsensorincorporatesa continuouslyvariableresistortogenerateananalogsignal. w Variableresistorchangesthesensor’sinternalresistancewiththe positionofthethrottle. w Thevoltageproducedbythesensorisalsocontinuouslyvariable;it isananalogsignal. w Thesignalcanbeanyvaluefrom0throughbatteryvoltage. Afuelgaugesenderisanotherdevicethatusesvariableresistanceto sendananalogsignal. Oscilloscope Display of Analog and Digital Signals Input and output signals can be either analog or digital. Fig. 6-02 TL623f602c Analog SignalsIntroduction to Electrical Symbols Electrical Circuit Diagnosis - Course 623 6-3 Temperatureandpositionsensors- Thesesensorsvaryinternal resistanceinresponsetotemperatureorposition.Thesignalisa varyingvoltageanalogtype. Analog Signals This sensor is a variable resistor that generates an analog signal. Fig. 6-03 TL623f603cSection 6 6-4 TOYOTA Technical Training Asignalthatrepresentsjusttwovoltagelevelsisadigitalsignal.A digitalsignalhasonlytwostates.Thesignalisnotcontinuously variable.Thetwostatescanbeexpressedinvariousways: w High/Low w ON/OFF w 1/0 Inatypicalautomotiveelectroniccircuit,adigitalsignaliseither0 voltsor+5volts. Example1- Aswitchisasimpledevicethatgeneratesadigitalsignal: w Switchopen =0volts(alsoLoworOFF) w Switchclosed =5volts(alsoHighorON) ElectronicControlUnits- ECUscanderiveorprovideinformation throughthesecharacteristicsofadigitalsignal: w Signalstate(ONorOFF) w Signalfrequency(howmanytimespersecondthesignalstate changefromhightolow) w Signalduration(howlongasignalstaysONorOFF) w Dutycycle(thepercentageoftimeONversustimeOFF) Digital Signal - Power Steering Pressure Switch A switch is an example of a digital signal producing device. The output is either on or off and produces either a high or low voltage. Fig. 6-04 TL623f604c Digital SignalsIntroduction to Electrical Symbols Electrical Circuit Diagnosis - Course 623 6-5 ElectronicControlUnitsmonitorinputs,processinputsignals,and generateoutputsignals. Inputs- SwitchesandsensorssendinputsignalstoECUs. w ThesesignalstelltheECUwhatishappeninginthesystemsitis controlling. w InputsignalsprovidetheECUwithinformationaboutoperating conditionsanddrivercommands. Outputs- ECUsareusedtocontrolvarioussystemsinthevehicle: w Engine w Automatictransmission w Climatecontrol w Cruisecontrol w Anti-lockbraking,tractioncontrol,andVSC w Accessorysystems OnetypeofECUisanEngineControlModule(ECM).AtypicalECM hastheseinputsignals: w Watertemperature w Air/fuelratio(oxygensensor) w Crankshaftposition w Camshaftposition w Throttleposition w Massairflow AnECMprocessestheinformationfromthesensorsandgenerates outputcommandstodevicesandsystemsthatcontrolengineoperation: w Ignition w Fuel Electronic Control UnitsSection 6 6-6 TOYOTA Technical Training Engine Control System An ECM processes information from sensors and generates output commands to control engine operation. Fig. 6-05 TL623f605cIntroduction to Electrical Symbols Electrical Circuit Diagnosis - Course 623 6-7 DividerElectronicControlUnitsmonitorsomesensorsusingavoltage dividercircuit. Avoltagedividercircuitistypicallyusedtogenerateavoltagethatis differentfromthesupply(battery)voltage. ECU Input - Voltage ECU’s monitor some sensors with voltage divider circuits. Fig. 6-06 TL623f606c ECU Input - Voltage DividerSection 6 6-8 TOYOTA Technical Training HowanElectronicControlUnitprocessesaninputdependsonthe signaltype. Digitalsignals- DigitalsignalsareinaformthatECUscanprocess directly. Analogsignals- ECUstypicallyconvertananalogsignaltoadigital signalbeforeprocessingtheinformation.Forexample,ananalogwheel speedsensorsignalisconvertedtoONandOFFpulsesforprocessing bytheABSECU. Look-uptables- ECUsprocessmostinputsignalsusinglook-up tables.Alook-uptableisasetofinstructions,oneforeachpossible conditiontheECUmaysee.Forexample,ifanECMsenses200 5F coolanttemperature,theinstructioninthelook-uptablemaytellitto turnonthecoolingfan.For125 5Fcoolanttemperature,theinstruction maybetoturnoffthecoolingfan. ECU Data Processing Analog signals are converted to digital signals before being processed by an ECU. Fig. 6-07 TL623f607c ECU Data ProcessingIntroduction to Electrical Symbols Electrical Circuit Diagnosis - Course 623 6-9 ECUsoperateavarietyofoutputdevicesincluding: w Doorlockactuators w Actuatorstooperateairredirectiondoorsinclimatecontrolsystems w Indicatorlamps(CheckEngine,etc.) w Ignitioncoil(s) ECU Output Signals After processing input signals, ECU’s output commands to various actuator devices. Fig. 6-08 TL623f608c ECU Output SignalsSection 6 6-10 TOYOTA Technical Training Troubleshootingelectroniccontrolunitsconsistsofconfirmingthree elements: w Inputdevice(sensor,switch)producestherequiredsignalsatthe timetheyareneeded; w ECUprocessesinputsignalsandproducestherequiredoutput signalsatthetimetheyareneeded; w OutputdevicerespondstoECU’ssignalsandoperatescorrectly. Anoscilloscope,alsocalledascope,“constructsavisualimageofan electronicsignal.Thisimagetakestheformofagraph.Likeanygraph, anoscilloscopeimageshowstwovalues: w ONTHEHORIZONTALAXIS-Thescopeshowsthepassageof timealongthehorizontalaxis(movingfromlefttoright).Theunits oftimearesetbyacontrolontheoscilloscope. w ONTHEVERTICALAXIS-Theimageonthescopedisplayshows voltagealongtheverticalaxis.Thehigherthesignalisfromthe bottomofthegraph,thehigheristhevoltagebeingrepresented. Oscilloscope Display An oscilloscope displays a visual representation of an electronic signal. Fig. 6-09 TL623f609 Troubleshooting with an OscilloscopeIntroduction to Electrical Symbols Electrical Circuit Diagnosis - Course 623 6-11 Anoscilloscopedisplayprovidesarecordofvoltageovertime. Example1- Connecttheoscilloscopeleadstoanautomotivebattery: w Scopedisplaysaconstanthorizontallineatabout12.6volts. w Thehorizontallineisconstantbecausethevoltageisnotchanging overtime. Oscilloscope Display - Battery Voltage This is what battery voltage looks like on an oscilloscope display. Fig. 6-10 TL623f610cSection 6 6-12 TOYOTA Technical Training Anoscilloscopedisplayprovidesarecordofvoltageovertime. Example2- Connecttheoscilloscopetotheoutputofathrottle positionsensor: w Holdthethrottlestationary,andthescopedisplaysaconstant horizontalline(voltageunchangingovertime). w Movethethrottlefromfullyclosedtofullyopen,andthescope displaysaslopinghorizontalline(voltageincreasesovertime). Oscilloscope Display - TPS Signal This is a TPS signal on an oscilloscope display. Fig. 6-11 TL623f600cIntroduction to Electrical Symbols Electrical Circuit Diagnosis - Course 623 6-13 Anoscilloscopedisplayprovidesarecordofvoltageovertime. Example3- Connecttheoscilloscopetothegroundsideofthecylinder #1fuelinjector: w SourcevoltageissuppliedtotheinjectorwhentheignitionisON. w TheECMcontrolsthegroundsideofthecircuit. w TheECMvariestheinjectorONtimetoadjusttheamountoffuel delivery. w TheONtimeisviewedasthedurationoftimewhenthereis0volts ontheground. w ThedurationwillvaryasinjectorONtimechangesduetofuel requirementsoftheengine. w Youcanadjustthetimesettingonthescopetorepresentthisvalue inascalethatisbestforinterpretation. Digitalsignalcharacteristics-Anoscilloscopedisplaycanrepresentall thecharacteristicsofadigitalsignal: w Voltage w Frequencyandpulsewidth(time) w Dutycycle(timeONversustimeOFF) Oscilloscope Display - Fuel Injector Signal This is the signal from a fuel injector. Fig. 6-12 TL623f612cSection 6 6-14 TOYOTA Technical Training
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