电子信息专业英语(9).ppt

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1、Unit4CommonInstrumentsPassageAAnalogInstrumentsandUsesNewWordsandExpressionsindicator['indikeitə]n.指示器permanent['pə:mənənt]adj.永久的calibration[kæli'breiʃən]n.刻度，标度，校准milliampere[mili'æmpεə]n.毫安hairspring['hεəspriŋ]n.细弹簧，游丝attraction[ə'trækʃən]v.吸引repulsion[ri'pʌlʃən]v.排斥milliammeter[mili'æm

2、itə]n.毫安表multiplier['mʌltiplaiə]n.乘法器permeability[pə:miə'biliti]n.渗透性torque[tɔ:k]n.扭矩，转矩electrodynamic[ilektrəudai'næmik]adj.电力学的，电动electrostatic[lektrə'stætik]adj.静电学的electrodynamicammeter电表Permanentmagnetmoving-coilinstrumentsfordirectcurrentsandvoltages:Thebasicprincipleisthatofamovingcoi

3、lwithattachedindicatorturninginthefieldofapermanentmagnetspeciallydesignedsothattheangularresponseofthemovingsystemisuniformandthecalibrationoftheinstrumentdoesnotchangeintimeduetochangesinthevalueofthefield.Tomeasurecurrentvaluesabove20milliamperes,whichwouldcauseoverheatinginthehairspringu

4、sedtoleadthecurrentintoandoutofthemovingcoil,ashuntisused,withamilliammeterconnectedinparallel.Themillimeterscaleismarkedintermsofthetotalcurrentintheshuntandtheinstrument.Tomeasurevoltages,thecurrenttakenbytheinstrumentmustbesmall.Henceaseriesresistorormultiplierisusedofavaluesuitabletogive

5、full-scaledeflectionwithacurrentintherange0.1-10milliamperes.Movingironinstrumentsofalternatingcurrentsandvoltages:Intheseinstrumentsthecurrentorvoltagetobemeasuredisusedtoexciteastationarycoilinwhosefieldsplacedamovingvaneofhighpermeablilitysteeltogetherwithaspringandpointer.Themotionofthev

6、aneissuchastoincreasethefluxthroughitandsothetorqueproducedbythereactionofthemagneticfieldsoftheelectromagnetandthevaneincreasestheinductanceofthecombination.Thetorqueincreaseswiththesquareofthecurrentinthecoilandasuitablescaleenablesthevaluestobereadoff.Thesemovingironinstrumentsareknownast

7、heattractiontype.Othersarecalledtherepulsiontype.Movingironinstrumentsoftherepulsiontypearealsocommon.Electrodynamicinstrumentsforthemeasurementofcurrentandvoltage:Theseinstrumentsaregenerallychosenforprecisionandcommerciallaboratorymeasurements.Th