高职电气自动化专业英语1ppt课件

.,Chapter1ElectricandElectronicTechnologyFundamentals,.,Unit1ElectricElementsandComponents,Text,NewWordsandExpressions,Exercises,End,.,Unit1ElectricElementsandComponents,IntroductionElectricalelementsareconceptualabstractionsusedintheanalysisofelectricalnetworks.Anyelectricalnetworkcanbeanalyzedasmultiple,interconnectedelectricalelementsinaschematicdiagramorcircuitdiagram,eachofwhichaffectsthevoltageinthenetworkorcurrentthroughthenetwork.Theseidealelectricalelementsrepresentreal,physicalelectricalorelectroniccomponentsbuttheydonotexistphysicallyandtheyareassumedtohaveidealpropertiesaccordingtoalumpedelementmodel,whilecomponentsareobjectswithlessthanidealproperties,adegreeofuncertaintyintheirvaluesandsomedegreeofnonlinearity,eachofwhichmayrequireacombinationof,.,multipleelectricalelementsinordertoapproximateitsfunctions.Circuitanalysisusingelectricelementsisusefulforunderstandingmanypracticalelectricalnetworksusingcomponents.Byanalyzingthewayanetworkisaffectedbyitsindividualelementsitispossibletoestimatehowarealnetworkwillbehave.,Unit1ElectricElementsandComponents,.,TheelementsThefourfundamentalcircuitvariablesarecurrent,I;voltage,V,charge,Q;andmagneticflux,.Only5elements,producedbymanipulatingthesefourvariables,arerequiredtorepresentanycomponentornetworkinaLinearsystem.Twosources:Currentsource,measuredinamperes-producesacurrentinawire.Anidealcurrentsourceisamathematicalmodel,whichrealdevicescanonlyapproachinperformance.Thecurrentthroughanidealcurrentsourceisindependentofthevoltageacrossit.,Unit1ElectricElementsandComponents,.,Voltagesource,measuredinvolts-producesapotentialdifferenceacrosstwopoints.Anidealvoltagesourceisonlyexistsinmathematicalmodelsofcircuits.Similarly,thevoltageacrossanidealvoltagesourceisindependentofthecurrentthroughit.Threepassiveelements:ResistanceR,measuredinohms-producesavoltageproportionaltothecurrentflowingthroughtheelement.RelatesvoltageandcurrentaccordingtotherelationCapacitanceC,measuredinfarads-producesacurrentproportionaltotherateofchangeofvoltageacrosstheelement.Relateschargeandvoltageaccordingtothe,Unit1ElectricElementsandComponents,.,relation,Unit1ElectricElementsandComponents,.,InductanceL,measuredinhenries-producesavoltageproportionaltotherateofchangeofcurrentthroughtheelement.Relatesfluxandcurrentaccordingtotherelation,.,.,TheComponentsAbatteryprovideselectromotiveforce(emf),orvoltage,inacircuit.Itcontainslayersofchemicalsthatcauseelectronstomoveinacertaindirection,fromitsnegativepoletoitspositivepole.Itismarkedwitharatingofhowmuchvoltagethereisacrossthetwopoles,anda(-)forthenegativepoleanda(+)forthepositivepole.Batteriesmayalsobemarkedwithanamperehour(Ah)rating,indicatingtotalchargecapacity.Anidealbatterycanthusberepresentedasavoltagesource.Inpractice,abatteryalsohasaninternalresistancethatisrepresentedasaresistanceinserieswiththevoltagesource.,Unit1ElectricElementsandComponents,.,Ifawireisusedtoconnectthetwopolesofabattery,electronsflowthroughthewirefromthenegativeendtothepositiveend.(Thewirewillalsogethotbecauseitisntaperfectconductor,andthebatterywillquicklyexhaustallitspower.)Thusawirecanberepresentedasalow-valueresistor.Currentsourcesareoftenabsentfrombasicelectriccircuits,andaremorelikelytobefoundinelectroniccircuitscontainingsemiconductors.Forexample,onafirstdegreeofapproximation,abipolar(junction)transistormayberepresentedbyavariablecurrentsourcethatiscontrolledbytheinputvoltage.,Unit1ElectricElementsandComponents,.,Aresistorisacomponentwhosefunctionistoregulatethecurrentinthecircuit.Onecommonkindisalittlecylinderofgraphitewithmetalwirescomingoutofeitherend.Thesearepaintedwithcoloredstripesthatindicatetheresistance,inohms,andthetolerance,inpercent.Thissystemiscalledtheresistorcolorcode.Anotherkindofresistorisafilament,whichisacoilofmetalwirethatcanwithstandhightemperaturebuthasafiniteresistance.Whenacurrentispassedthroughafilament,itheatsupbecauseofthisresistance.Filamentsarecommonlyusedinlightbulbsandheaters.Theyaremarkedwiththevoltagethatshouldbeappliedtothem,andthepower,inwatts,thattheywillthengiveoffaslightandheat.Duetotheeffectofheating,afilamentsresistanceishigherwhenitishotthanwhenitiscold.,Unit1ElectricElementsandComponents,.,Anelectricchargecanbestoredandthenquicklyreleasedbyacomponentcalledacapacitor.Acommontypeofcapacitorconsistsoftwopiecesofmetalfoil(orplates)withaninsulator(thedielectric)suchaswaxedpaperbetweenthem.Ifanelectricchargeisplacedontheplatesofacapacitor,itwillstaytherebecauseitcantcrosstheinsulatortotheotherplate.Ifawireisthenconnectedbetweenthetwoplates,thechargewillflowthroughthewiretobalancethechargesontheoppositeplatesthecapacitoristhensaidtobedischarged.,Unit1ElectricElementsandComponents,.,Unit1ElectricElementsandComponents,Somecapacitorslooklikeacylinderorblobwithtwowirescomingoutoneend,andaremarkedtoindicatetheircapacitance(thechargethattheystorepervolt)inmicrofarads(F),nanofarads(nF)orpicofarads(pF).Inductanceinacircuitisprovidedbycomponentscalledinductors,whicharealmostalwaysbuiltfromcoilsofwire.Largevaluesofinductanceareobtainedbyformingthecoilaroundamagneticcore,suchasalumpofironorferrite.Inductanceisalsopresentinthewindingsofelectricmotorsandgenerators,andtoalesserextentinanypieceofwire.,.,Elementsvs.ComponentsThereisadistinctionbetweenreal,physicalelectricalorelectroniccomponentsandtheidealelectricalelementsbywhichtheyarerepresented.Electricalelementsdonotexistphysically,andareassumedtohaveidealpropertiesaccordingtoalumpedelementmodel.Conversely,componentsdoexist,havelessthanidealproperties,theirvaluesalwayshaveadegreeofuncertainty,theyalwaysincludesomedegreeofnonlinearityandtypicallyrequireacombinationofmultipleelectricalelementstoapproximatetheirfunctions.,Unit1ElectricElementsandComponents,.,NewWordsandExpressions,currentn.电流alternatingcurrent交流电流directcurrent直流电流currentdensity电流密度activecurrent有功电流reactivecurrent无功电流voltagen.电压voltagedrop电压降落voltagegain电压增益voltagedivider分压器voltagestabilizer稳压器,.,NewWordsandExpressions,variablen.变量；a.可变的，可调的，易变的complexvariable复变量dependentvariable因变量independentvariable自变量inputvariable输入变量chargen.电荷，充电；v.充电，带电，起电chargedistribution电荷分布chargeparticle带电粒子testcharge试验电荷positivecharge正电荷negativecharge负电荷,.,NewWordsandExpressions,coulombn.库仑（电荷的单位）coulombmeter库仑计circuitn.电路circuitdiagram电路图analoguecircuit模拟电路shortcircuit短路opencircuit开路activecircuit无源电路passivecircuit无源电路underlyinga.基本的，根本的潜在的，在下（面）的，下伏的,.,NewWordsandExpressions,conceptualadj.概念上的abstractionn.抽象lumpedelementmodel集总参数元件模型areobjectswith倾向于nonlinearityn.非线性特性chargen.电量fluxn.磁通量idealcurrentsource理想电流源potentialdifference电势差idealvoltagesource理想电压源passiveelement无源元件ohmn.欧姆resistancen.电阻capacitancen.容量,电容faradn.法拉(电容单位)inductancen.电感henriesn.亨利(电感单位)electromotiveforce电动势negativepole负极positivepole正极exhaustvt.用尽,耗尽cylindern.圆柱体graphiten.石墨coloredstripe色环tolerancen.额定容量filamentn.金属丝withstandvt.抵挡,经受住capacitorn.电容器nanofaradn.微法(拉)picofaradn.皮法拉inductorn.感应器lumpn.块(尤指小块)ferriten.铁氧体,Return,.,Exercises,I.MarkthefollowstatementswithTorFaccordingtothetext.,Thereisntadistinctionbetweenreal,physicalelectricalorelectroniccomponentsa