专业英语课件.ppt

自动化专业英语,SpecializedEnglishforAutomation,PARTIELECTRONICS,1ElectricalMeasuringInstruments2FundamentalsofSolid-statePowerDevice3AnalogElectronics4DigitalElectronics,PARTIIELECTRICALMACHINE,CONTROLCOMPONENTANDSENSOR,5IntroductiontoElectricalMachines6DCMotorAndInductionMotor7ElectricalMachineControlSystem8ControlSensors,1ElectricalMeasuringInstruments第1章电子测量仪表,1.1SafetyPrecaution(安全措施)1.2BasicMeterConstructionandOperation(基本仪表构造和操作)1.3UseofMeasuringInstrument(测量仪表的使用)1.3.1VoltageTesters电压测量计1.3.2Voltmeters伏特表1.3.3Ammeters安培表1.3.4Ohmmeter欧姆表,1ElectricalMeasuringInstruments第1章电子测量仪表,1.1SafetyPrecaution(安全措施)1.2BasicMeterConstructionandOperation(基本仪表构造和操作)1.3UseofMeasuringInstrument(测量仪表的使用)1.3.5CoutinuityTester导通测试仪1.3.6Megohmmeter兆欧表1.3.7Multimeters万用表1.3.8Wattmeter瓦特计1.3.9WatthourMeters瓦时表,Vocabulary1.personnelp:sneln.人员，职员2.voltmetervultmi:tn.电压表，伏特计(表)3.ohmmeterummi:tn.欧姆计，电阻表4.megohmmetermeumi:tn.兆欧表5.wattmeterwtmi:tn.瓦特表(计),电表,功率(W)6.watt-hourn.瓦时，瓦特小时(能量单位)7.ammetermitn.安培计,电流表,Vocabulary8.calibrateklbretv.校正(准)9.scaleskeiln.刻度,量程10.ratedadj.额定的11.interferewith有害于12.indicatingneedle(仪表)指针13.hazardoushzdsadj.危险的pivotpvtn.支点,Vocabulary15.terminalt:minln.接线端子16.spiralspairladj.螺旋形的17.springn.弹簧18.shuntntn.分流；分路(流)器；并联、旁路19.rectifiern.整流器20.electrodynamometerilektrudainmmitn.电测力计21.striveforv.争取22.vanevenn.(机器的)叶，叶片,Vocabulary23.stripstrpn.条,带,片24.crudekru:dadj.不精细的，粗略的25.polarityplrtin.极性26.fusefju:zn.保险丝，熔丝27.ruggedrgdadj.坚固的28.depictdipiktv.描绘，描写29.cartridgefusek:trid盒式保险丝,Vocabulary30.blowbluv.(保险丝)烧断31.plugfuse插头式保险丝32.malfunctionmlfknn.故障33.deenergizev.不给.通电34.insulationnslenn.绝缘35.generatordenreitn.发电机36.magnetomni:tun.磁发电机,Vocabulary37.humidityhju:miditin.湿度38.moisturemistn.潮湿，湿气39.abbreviatebri:vi:etv.缩写，缩写为abbr.40.transformern.变压器41.thumbmv.检查，查阅,拇指42.milliammetermilimi:tn.毫安表,Vocabulary43.multimetern.万用表44.dynamometerdainmmitn.测力计，功率计45.aluminumlu:mnmn.铝46.deteriorateditirireitv.(使)恶化47.eddycurrent涡流48.gearn.齿轮，传动装置49.dialdaln.刻度盘,Electricalpersonnelusemanydifferenttypesofmeasuringinstruments.,从事电子技术的专业人员要使用各种类型的测量仪表。,Test,Somejobsrequireveryaccuratemeasurementswhileotherjobsneedonlyroughestimates,someinstrumentsareusedsolelytodeterminewhetherornotacircuitiscomplete.,该句为复合句,somejobs.otherjobs.someinstruments引导并列主句,whetherornot引导areused的状语从句。,Test,Somejobsrequireveryaccuratemeasurementswhileotherjobsneedonlyroughestimates,someinstrumentsareusedsolelytodeterminewhetherornotacircuitiscomplete.,一些工作需要非常精确的测量，而另一些工作仅需要粗略的估计，还有些仪表主要用来测量电路是否接通。,Test,Themostcommonmeasuringandtestinginstrumentsarevoltagetesters,voltmeters,ammeters,ohmmeters,continuitytesters,megohmmeters,wattmeters,andwatt-hourmeters.,最常用的测量和检测仪表是：电位差计、伏特表、安培表、欧姆表、通路测量仪、兆欧表、瓦特表、瓦时计量器。,Allmetersusedformeasuringelectricalvaluesarebasicallycurrentmeters.Theymeasureorcomparethevaluesofcurrentflowingthroughthem.Themetersarecalibratedandthescaleisdesignedtoreadthevalueofthedesiredunit.,划线一句为两个短句构成的并列句型,主语分别是meters和scale,toread是isdesigned的目的状语。注意被动语态的译法。,Allmetersusedformeasuringelectricalvaluesarebasicallycurrentmeters.Theymeasureorcomparethevaluesofcurrentflowingthroughthem.Themetersarecalibratedandthescaleisdesignedtoreadthevalueofthedesiredunit.,所有用来测量电子值的仪表基本上是电流表。它们测量或比较流经仪表的电流。这些仪表可以被校准并设计好量程,以便读出期望的数值。,1.1SafetyPrecaution,第一节安全措施,Correctmeterconnectionsareveryimportantforthesafetyprecautionoftheuserandforpropermaintenanceofthemeters.,仪表的正确连接对使用者的安全预防措施以及仪表的正确维护都十分重要。,1.1SafetyPrecaution,第一节安全措施,Abasicknowledgeoftheconstructionandoperationofmeterswillaidtheuserinmakingproperconnectionsandmaintainingtheminsafeworkingorder.,该句是一个简单句,短语aidsb.indoingsth帮助某人做某事making.andmaintaining是并列结构的介词宾语,1.1SafetyPrecaution,第一节安全措施,Abasicknowledgeoftheconstructionandoperationofmeterswillaidtheuserinmakingproperconnectionsandmaintainingtheminsafeworkingorder.,(懂得)仪表构造与操作的基本知识会确保使用者正确使用以及安全工作。,ManyinstrumentsaredesignedtobeusedonDCorAConly,whileotherscanbeusedinterchangeably.,该句为两个并列的句子,while引导相反的句意,可译为“然而”、“而”。interchangeably可交换地;可替换地inter-表示“在之间，相互”interaction相互影响international国际的,许多仪表被设计为仅用于在交流或直流电路中,而其他的可以交换使用。,Itisimportantthat/todo.句型,which引导定语从句。类似的句型还有：Itisnecessary/called/definedas/saidtobee有必要./.称作/.定义为./据说.Itseemsessentialtogiveadetailedstudy.似乎有必要进行细致的研究,Note:Itisveryimportanttouseeachmeteronlywiththetypeofcurrentforwhichthemeterisdesigned.,注意：每种仪表只能用来测量符合设计要求的电流类型，这一点十分重要。,Note:Itisveryimportanttouseeachmeteronlywiththetypeofcurrentforwhichthemeterisdesigned.,名词化结构usingameterwithanincorrecttypeof.做主语，可简化句子结构。比较一下：Ifweuseameterwithanincorrecttypeofcurrent,itcanresultin.名词化结构可减少if从句,避免人称代词。,Usingameterwithanincorrecttypeofcurrentcanresultindamagetothemeterandmaycauseinjurytotheuser.,用在不正确的电流类型下使用会导致仪表毁坏,乃至使使用者受到伤害。,Usingameterwithanincorrecttypeofcurrentcanresultindamagetothemeterandmaycauseinjurytotheuser.,一类仪表仅用来测量很小的值，另一类能用来测量极大值。,Somemetersareconstructedtomeasureverylowvalues.Othermeterscanmeasureextremelyhighvalues.,CAUTION:Neverallowammetertoexceeditsratedmaximumlimit.Theimportanceofneverallowingtheactualvaluetoexceedthemaximumvalueindicatedonthemetercannotbeoveremphasized.,划线一句是名词性结构neverallowingthevalue.为了简化句子结构,减少if从句；indicatedon过去分词短语做后置定语修饰先行词value。,CAUTION:Neverallowammetertoexceeditsratedmaximumlimit.Theimportanceofneverallowingtheactualvaluetoexceedthemaximumvalueindicatedonthemetercannotbeoveremphasized.,警告：不允许仪表超出它的额定最大量程。不允许被测的实际数值超过仪表最大允许值的要求再强调也不过分。,Exceedingmaximumvaluescandamagetheindicatingneedle,interferewithpropercalibration,andinsomeinstancesmaycausethemetertoexplode,resultingininjurytotheuser.,名词性结构exceedingmaximumvalues做主语,谓语动词是erferewith.maycause.resultingin.分词短语做maycause的结果状语。,Exceedingmaximumvaluescandamagetheindicatingneedle,interferewithpropercalibration,andinsomeinstancesmaycausethemetertoexplode,resultingininjurytotheuser.,超出最大值会导致仪表指针的损坏,妨碍正确的校准,在某些情况下还可能引起仪表的爆炸,伤害使用者。,Somemetersareequippedwithovercorrectprotection.However,acurrentmanytimesgreaterthantheinstrumentsdesignlimitmaystillbehazardous.,一些仪表备有过电流保护。time的译法,比较下列两句：(1)但是,电流多次超出仪表的设计范围仍然是危险的。(2)但是,电流超出仪表的设计限定值许多倍仍然是危险的。,electromagneticinteraction电磁感应operateon基于.工作/运行,许多仪表都是基于电磁感应原理工作的。,1.2BasicMeterConstructionandOperation,第二节基本仪表构造和操作,Manymetersoperateontheprincipleofelectromagneticinteraction.,Thisinteractioniscausedbyanelectriccurrentflowingthroughaconductorwhichisplacedbetweenthepolesofapermanentmagnet.,1.2BasicMeterConstructionandOperation,第二节基本仪表构造和操作,复合句。主句interactioniscausedby.current;flowingthrough.现在分词短语做后置定语,修饰current;which引导aconductor的定语从句。,Thisinteractioniscausedbyanelectriccurrentflowingthroughaconductorwhichisplacedbetweenthepolesofapermanentmagnet.,这种感应是由电流流经一个放置在永久磁铁两极间的导体时引起的。,1.2BasicMeterConstructionandOperation,第二节基本仪表构造和操作,Thistypeofmeterisespeciallysuitablefordirectcurrent.,这种类型的仪表尤其适用于直流。,1.2BasicMeterConstructionandOperation,第二节基本仪表构造和操作,whenever引导时间状语从句，主句为被动句，译成主动语态。,Wheneveranelectriccurrentflowsthroughaconductoramagneticforceisdevelopedaroundtheconductor.,无论何时,只要一个电流流经一个导体,在这个导体周围就形成一个磁力。,Themagneticforcecausedbytheelectriccurrentreactswiththeforceofthepermanentmagnet.Thiscausestheindicatingneedletomove.,第一句主谓结构,causedby.过去分词短语做后置定语,修饰magneticforce(磁力)。电流引起的磁力与永久磁铁相互作用,引起指针的移动。,Thelargertheamountofcurrent,thefarthertheneedlewillmove.,句型theadj.比较级.theadj.比较级.表示“越.越.”电流越大，指针移动的越远。,which引导非限定性定语从句,翻译时可作为两个分句。将导线绕成线圈，放在永久磁铁的两极中间的一个轴上。,Theconductorisformedintocoil,whichisplacedonapivotbetweenthepolesofthepermanentmagnet.,Thecoilisconnectedtotheterminalsoftheinstrumentthroughtwospiralsprings.,oftheinstrument做后置定语,throughtwospiralsprings做方式状语。通过两个螺旋型弹簧线圈线圈与仪表的接线端子相连。,Thesespringssupplyareactingforceproportionaltothedeflection.Whennocurrentisflowing,thespringscausetheneedletoreturntozero.,第一句中proprotionalto.形容词短语做后置定语。reactingforce反作用力第二句cause.toreturntozero注意翻译简洁明了。,Thesespringssupplyareactingforceproportionaltothedeflection.Whennocurrentisflowing,thespringscausetheneedletoreturntozero.,这些弹簧提供了与偏移量成正比的反作用力。当没有电流流动时,弹簧使指针返回到零点。,beingmeasured过去分词的现在时态表示“正在进行测量的”,这是中英文的区别。scale词义有“刻度”、“量程”仪表刻度是设计用来指示被测电流量。,Themeterscaleisdesignedtoindicatetheamountofcurrentbeingmeasured.,Themovementofthecoil(andthusthemovementoftheindicatingneedle)isproportionaltotheamountofcurrentflowinginthecoil.,该句是主系表结构,flowingin现在分词短语做后置定语。线圈的移动(以及由此引起的指针的移动)和流经线圈的电流成比例。,Ifitisnecessarytomeasurelargercurrentsthanthecoilcansafetycarry,abypasscircuit,orshunt,isincluded.Theshuntmanybecontainedwithinthemeterhousingorconnectedexternally.,bypass旁路,passby经过;shunt分路如果要去测量一个大于线圈所能安全承载的电流时,有必要安装一个旁路,或者分路。分路可以包含在仪表箱内,也可联接在外面。,Example1Ameterisconstructedtomeasureto10Aonamaximumscale.Thecoilcansafelycarry0.001A.theshuntmustbedesignedtocarry9.999A.,例一:一个仪表设计测量的最大量程为10A。线圈所能安全流过的电流为0.001A,则旁路必须设计来承担9.999A的电流。,Themeterisdesignedtoindicate10Awhen0.001Aflowsinthecoil.,when引导时间状语,翻译时应作为前置状语,以符合中文的表达习惯。当有0.001A的电流流经线圈时仪表应指示10A。,Shunt“分路”、“并联”、“分流器”,此处是“分流器”更合理。图1.1(a)是一个永磁仪表。图1.1(b)是通过仪表接线端子外接的分流器。,Fig.1.1(a)illustratesapermanent-magnet.Fig.1.1(b)showanexternalshuntconnectedacrossthemeterterminal.,Thepermanent-magnetmetercanbeusedasanammeteroravoltmeter.Whenthescaleisdesignedtoindicatecurrentandtheinternalresistanceiskepttoaminimum,themeterfunctionsasanammeter.,When引导时间状语,thescaleis.andtheinternalresistanceis.为并列两个分句永磁式仪表可作安培表或伏特表。当刻度表示电流且内部电阻很小时,仪表做安培表使用。,Whenthescaleisdesignedtoindicatevoltage,theinternalresistancewillberelativelyhigh,dependinguponthevalueofvoltageforwhichthemeterisdesigned.,Dependingupon现在分词短语做状语,进一步说明high的程度。当刻度指示电压,内阻相对高一些,且内阻取决于仪表可测电压的设计值。,Note:Regardlessofthedesign,thedistancetheneedlemovesisdeterminedbytheamountofcurrentflowinginthecoil.,Regardlessof不管怎样,主句为被动句,应译为主动语态。注意:不管怎样设计,指针移动的距离由流经线圈的电流量决定。,第二句是“定义”句型,译为“.的装置”为了在交流电中使用这种仪表,必须在设计上稍做改动。整流器是一个把交流转化为直流的装置。,AslightchangemustbemadeinthedesigninordertousethistypeofmeteronAC.ArectifierisadevicewhichchangesACtoDC.,ItmustbeincorporatedintothemeterandthescalemustbedrawntoindicatethecorrectvalueofACvoltage.Rectifier-typeACmeterscannotbeusedonDCandaregenerallydesignedasvoltagemeters.,两句均是被动句,译为主动式。bedrawnto“被吸引到”,此处可“意译”,ItmustbeincorporatedintothemeterandthescalemustbedrawntoindicatethecorrectvalueofACvoltage.Rectifier-typeACmeterscannotbeusedonDCandaregenerallydesignedasvoltagemeters.,它必须和仪表结合在一起,刻度必须指示正确的交流电压值。整流器类型的交流仪表不能用在直流中,而且一般被设计做电压表。,Theelectrodynamometer与Fig.1.2是同位语。That引导定语从句,先行词在从句中做主语电测力计,如图1.2所示,是另一种用在交流电下工作的仪表,它既可用作安培表,又可用作伏特表。,Theelectrodynamometer,Fig.1.2isanotherdesignforbothammetersandvoltmetersthatcanbeusedonalternatingcurrent.,Thisinstrumentconsistsoftwostationarycoilsandonemovablecoil.Thethreecoilsareconnectedinserieswitheachotherthroughtwospiralsprings.,consistof(整体)由(部件)组成stationarycoil静止线圈;movablecoil动线圈inserieswith串联;inparallelwith并联这种仪表由两个静止线圈和一个动线圈构成。三个线圈通过两个螺旋式弹簧串接在一起。,Thespringalsosupportthemovablecoil.Whencurrentflowsthroughthecoilsthemovablecoilmovesinaclockwisedirection.,clockwise顺时针;counterclock逆时针anticlockwise英/counterclockwise美逆时针弹簧也支撑动线圈,当电流流经线圈时,动线圈向顺时针方向移动。,第一句isnot.asitis.不像.一样.varieswith随.变化;square平方在电测力计内,刻度不像在永磁仪表那样均匀划分。作用在动线圈上的力随着线圈电流的平方而变化。,Intheelectrodynamometer,thescaleisnotdivideduniformly,asitisinpermanentmagnet-typemeters.Theforceonthemovablecoilvarieswiththesquareofthecurrentflowingthroughthecoils.,Thisrequiresthatthedivisionsnearthebeginningofthescalebemadeclosertogetherthanthosenearend.,requirethat.(should)dosth.这要求刻度在开始处时密一些,而在结束处要疏一些。,Thegreaterthedistancebetweenthedivisions,themoreaccuratelyonecanreadthemeter.Itisimportanttostriveforanaccuratereading.,Thegreater.themore.越.越.第一句为了句子平衡将read的状语提前。刻度间的间隔越大,从仪表上读出的数据就越精确。这对争取一个精确的读数很重要。,动叶片结构是仪表的另一种结构。在线圈内流动的电流使两个铁条磁化。一个叶片可动另一个固定。,Themoving-vanemeterisanothertypeofconstructionformeters.Currentflowinginthecoilcausestwoironstrips(thevanes)tobecomemagnetized.Onevaneismovable;theotherisstationary.,Themagneticreactionbetweenthetwovanescausesthemovableonetoturn.Theamountofmovementdependsuponthevalueofcurrentflowinginthecoil.,两个叶片间磁的作用使动叶片转动。其移动位移取决于流经线圈的电流值。,警告:以上叙述的所有仪表都以磁学作为操作原理,所以不要把它们放置在靠近其它磁体附近,这一点很重要。,CAUTION:Alloftheinstrumentsdescribeddependuponmagnetismfortheiroperation,soitisimportantthattheynotbeplacednearothermagnets.,Themagneticforcefromanothermagnetmaydamagethemeterand/orcauseincorrectmeasurements.,该句是主谓宾结构,谓语maydamage.and/orcause另一个磁体的磁场会对仪表造成损害和/或导致测量结果不正确。,1.3UseofMeasuringInstrument,第三节测量仪表的使用,electricalpressure电压,component元件applied与acrossacomponent介词短语做后置定语,先行词是voltagedrop电压伏特表是用来测量电路中的电压和/或一个元件的电压降。,Avoltmeterisdesignedtomeasuretheelectricalpressureappliedtoacircuitand/orthevoltagedropacrossacomponent.,Voltmetersmustalwaysbeconnectedinparallelwiththecircuitorthecomponentbeingmeasured.,它(电压表)必须与被测电路或元件并联。,crudeadv.相当地;approximateadj.近似的对电工来说,交直流电位检测计是一个虽不太精确但十分有用的仪表。,1.3.1VoltageTesters电位差计,TheAC-DCvoltagetesterisarathercrudebutusefulinstrumentfortheelectrician.Thisinstrumentisdesignedtoindicateapproximatevaluesofvoltage.,Themorecommontypesindicatethefollowingvaluesofvoltage:AC,110,220,440,and550V;DC,125,250,and600V.Manyoftheseinstrumentswillalsoindicatethe“polarity”ofDC;i.e.,whichconductorofthecircuitispositivelyornegativelycharged.,i.e.=thatis“即”;positive正(极)的negative负(极)的其较常用的类型有以下几种电压等级:交流110,220,440和550V;直流125,250和600V。许多这样的仪表也指示直流电的极性,也就是电路的元件哪个带正电荷或负电荷。,Thevoltagetesterisusedtocheckcommonvoltages,toidentifythegroundedconductor,tocheckforblownfuses,andtodistinguishbetweenACandDC.,Beusedtodo译为”用来”Tocheck.toidentify.tocheck.andtodistinguish并列结构的目的状语电位检测计用来检查公共电压,识别接地导体,查保险丝是否烧断,区分交流和直流。,Thevoltagetesterissmallandrugged,makingiteasiertocarryandstorethantheaveragevoltmeter.Fig.1.3and1.4depictmethodsfortestingfuseswithavoltagetester.,电位检测计小巧结实,比一般的伏特表便于携带保存。图1.3和1.4描述了用电位检测计检查保险丝的方法。,cartridgefuse熔丝管,plugfuse插式保险丝,主句是祈使句,todetermine引导目的状语为了确定一个电路中或一个系统的哪一个导体接地，把检测计连接在一个元件和一个已建立的地之间。,Todeterminewhichconductorofacircuitorasystemisgrounded,connectthetesterbetweenoneconductorandawellestablishedground.,Ifthetesterindicatesavoltage,theconductorisnotgrounded.Continuethisprocedurewitheachconductoruntilzerovoltageisindicated(seeFig.1.5).,第二句是祈使句。until直到.才.如果检测计指示出一个电压,则导体没有接地。对每一个导体重复这样的步骤,直到指示零电压出现(如图1.5)。,anytwoconductor与后面的thetwoconductors指代的是同样的对象,翻译时注意。为了得到任何两个导体间的近似电压值,把电压检测计连接在这两个导体之间。,Todeterminetheapproximatevoltagebetweenanytwoconductors,connectthetesterbetweenthetwoconductors.,CAUTION:Alwaysreadandfollowtheinstructionsthataresuppliedwithvoltagetester.,that引导定语从句instruction指示,说明书。警告:经常读并遵守电压检测计的使用说明进行操作。,1.3.2Voltmeters伏特表/电压表,电压表是一个比电压检测计精确得多的测量仪表。由于伏特表与被测电路或元件相并联,故要求它们有相对高的电阻。,Becausevoltmetersareconnectedinparallelwiththecircuitorthecomponentbeingconsidered,itisnecessarythattheyhaverelativelyhighresistance.,Thevoltmeterisamuchmoreaccuratemeasurementthanthevoltagetester.,thelower.theless越.越.electricalcharacteristics电路特性内阻使流经表的电流保证最小。流经仪表的电流越小,对电路特性上的影响越小。,Theinternalresistancekeepsthecurrentthroughthemetertoaminimum.Thelowerthevalueofcurrentthroughthemeter,thelesseffectithasontheelectricalcharacteristics.,电工使用的普通仪表的精度一般介于95%98%之间。这个精度范围对大多数应用是满意的。,Theaveragemeterusedbytheelectricianisgenerallybetween95percentand98percentaccurate.Thisrangeofaccuracyissatisfactoryformostapplications.,Itisveryimportant,however,thattheelectricalworkerstrivetoobtainthemostaccuratereadingpossible.Anaccuratereadingcanbeobtainedbystandingdirectlyinfrontofthemeterfaceandlookingdirectlyatit.,第二句by.做方式状语,bystanding.and(by)looking.缩写句子。,然而,电工力求最精确的读数是重要的。站在表盘的正前方且直视,才可能得到一个精确的读数。,Itisveryimportant,however,thattheelectricalworkerstrivetoobtainthemostaccuratereadingpossible.Anaccuratereadingcanbeobtainedbystandingdirectlyinfrontofthemeterfaceandlookingdirectlyatit.,Ifthemeterhasamirrorbehindthescale,adjusttheangleofsightuntilthereisnoreflectionoftheindicatingneedleinthemirror.Forextremeaccuracy,adigitalmetermaybeused.,scale”刻度”,angleofsight”视线的角度”reflection影子,indicatingneedle指针,Ifthemeterhasamirrorbehindthescale,adjusttheangleofsightuntilthereisnoreflectionoftheindicatingneedleinthemirror.Forextremeaccuracy,adigitalmetermaybeused.,如果仪表的刻度后面有镜子,调整视线的角度，直到指针在镜中没有反射为止。如要更精确可使用数字表。,Voltmeterscanbeusedforthesameapplicationsasvoltagetesters.Voltmetersaremuchmoreaccuratethanvoltagetesters.Therefore,muchmoreinformationcanbeobtained.,电压表和电压检测计具有同样的用途。它比电压检测计更精确。因此,可以读取更多的信息。,Forexample,ifthevoltagetoabuildingisslightlybelownormal,thevoltmetercanindicatethisproblem.Thevoltmetercanalsobeusedtodeterminetheamountofvoltagedroponfeederandbranchcircuitconductors.,例如,如果一个建筑物的供电电压稍低于正常值,电压表就能指出这个问题。电压表也用来确定馈电线和支线电路导体的压降值。,arangeselectorswith量程选择开关电压表有时有多个量程。选择能够提供最精确测量值的量程很重要。量程选择开关就可达到这种目的。,Voltmeterssometimeshavemorethanonescale.Itisveryimportanttoselectthescalethatwillprovidethemostaccuratemeasurement.Arangeselectorswitchisprovidedforthispurpose.,Note:Itisadvisabletobeginwithahighscaleandworkdowntothelowestscalesoasnottoexceedtherangelimitofanyscale.,advisableadj.明智的,可取的itisadvisabletodo.做.是可取的/建议.workdown逐渐降低;soasnotto以免.注意：建议从高量程开始逐渐向低量程过渡，以免超出量程的限制。,Settingtheselectorswitchonthelowestusablescalewillprovidethemostaccuratereading.,settingtheselectorswitch名词化短语做主语,可简化句子结构,省略if从句。把量程开关设在最低能用的量程处能得到最精确的读数。,beforeusingthemeter名词性短语结合before做时间状语,简化句子结构。justbelow正下方在使用仪表以前,检查以确保指针指向零刻度。表盘正下方有一个调节螺丝。,Beforeusingthemeter,checktobesurethattheindicatingneedleispointingtozero.Anadjustmentscrewisprovidedjustbelowthefaceofthemeter.,Averyslightturnwillcausetheneedletomove.Theneedlecanbealignedwiththezerolineonthescalebyturningthescrew.,move译为”偏转”bealignedwith与.相一致轻微扭动就会引起指针的偏转。通过扭动这个螺丝可以使指针和零刻度线相重合。,whenusingvoltmeters名词性短语做时间状语polarity极性;positive正极negative负极,WhenusingvoltmetersonDC,itisveryimportanttomaintainproperpolarity.MostDCpowersuppliesandmetersarecolorcodedtoindicatethepolarity.Redindicatesthepositiveterminal;blackindicatesthenegativeterminal.,在直流电中使用电压表时,保证极性的正确连接很重要。大多数直流电源和仪表都以颜色来指示极性。红色表示正极接线端,黑色表示负极接线端。,WhenusingvoltmetersonDC,itisveryimportanttomaintainproperpolarity.MostDCpowersuppliesandmetersarecolorcodedtoindicatethepolarity.Redindicatesthepositiveterminal;black