教学材料《汽车构造英语》-Unit11

UnitElevenTestingToolsMultimetersarerelativelyinexpensive.Multimetersareavailableindigitalandanalogmodels.Digitalmultimeterswilldisplayreadingsinnumbers，usuallyonaliquidcrystaldisplay.Analogmultimetersindicatevalueswithaneedleoverascale.2

Youcanuseamultimetertotestmotors，switches，controllers，andmanyotherelectricalgadgets(seeFig11-1).Specificinstructionswillcomewiththemultimeter(alsocalledavoltohmmeterorVOM)youpurchase.上一页返回下一页UnitElevenTestingToolsHere’showtouseamultimetertotestanelectricappliance(seeFig.11-2andFig.11-3)1.Disconnectthecordfromthepowersource，exceptwhentestingalivecircuit.2.Plugthetestleadsintothemultimeter.3.Selectthefunction(ACV，DCV，RESISTANCE)andtherange(maximumreadingexpected).4.Connecttheprobestothecordorappliancecomponent.5.Interpretthereading.上一页返回下一页UnitElevenTestingToolsNotes1.Acontinuitytesterchecksresistance，butanswersYESorNO.通路测试仪只能检测电路导通还是断路。2.Analogmultimetersindicatevalueswithaneedleoverascale.指针式万用表根据指针在刻度上的位置来显示出测量数据。上一页返回下一页UnitElevenTestingToolsExtraReadingAnalogMultimeters

Ananalogmetermovesaneedlealongascale.Switchedrangeanalogmultimetersareverycheapbutaredifficultforbeginnerstoreadaccurately，especiallyonresistancescales.Themetermovementisdelicateanddroppingthemeterislikelytodamageit!Eachtypeofmeterhasitsadvantages.Usedasavoltmeter，adigitalmeterisusuallybetterbecauseitsresistanceismuchhigher，1MΩor10MΩ，comparedto200KΩforananalogmultimeteronasimilarrange.上一页返回下一页UnitElevenTestingToolsOntheotherhand，itiseasiertofollowaslowlychangingvoltagebywatchingtheneedleonananalogdisplay.Usedasanammeter，ananalogmultimeterhasaverylowresistanceandisverysensitive，withscalesdownto50μA.Moreexpensivedigitalmultimeterscanequalorbetterthanthisperformance.Mostmodernmultimetersaredigitalandtraditionalanalogtypesaredestinedtobecomeobsolete.上一页返回Fig.11-