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 Relatesvoltageandcurrentaccordingtotherelation CapacitanceC 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 Thewirewillalsogethotbecauseitisn taperfectconductor 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 afilament sresistanceishigherwhenitishotthanwhenitiscold Unit1ElectricElementsandComponents Anelectricchargecanbestoredandthenquicklyreleasedbyacomponentcalledacapacitor Acommontypeofcapacitorconsistsoftwopiecesofmetalfoil orplates withaninsulator thedielectric suchaswaxedpaperbetweenthem Ifanelectricchargeisplacedontheplatesofacapacitor itwillstaytherebecauseitcan tcrosstheinsulatortotheotherplate Ifawireisthenconnectedbetweenthetwoplates thechargewillflowthroughthewiretobalancethechargesontheoppositeplates thecapacitoristhensaidtobedischarged 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 Thereisn tadistinctionbetweenreal physicalelectricalorelectro