专业英语第8单元作业

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1、ControlSensors8.1INTRODUCTIONInfeedbackcontrolsystem一plant（设备）responseismeasuredandcomparedwithareferenceinputandtheerrorisautomaticallyemployedincontrollingtheplant.Itfollowsthatameasurementsystemisanessentialcomponentinanyfeedbackcontrolsystemandformsavitallinkbetweentheplantandthecontro

2、ller.Measurementsareneededinmanyengineeringapplications.Themeasurementprocesshastobeautomated,however,incontrolsystemsapplications.Atypicalmeasurementsystemconsistsofoneormoresensor-transducerunitsandassociatedsignal-conditioning（信号调理）（andmodification改善）devices（seeFig.8.1）.Filteringtoremov

3、eunwantednoiseandamplificationtostrengthenaneededsignalareconsideredsignalconditioning.Analog-to-digitalconversion（ADC）,digital-to-analogconversion（DAC）,modulation（调制），anddemodulation（解调）aresignalmodification（信号增强、信号改善）methods.Notethatsignalconditioningcanbeconsideredunderthegeneralheading

4、ofsignalmodification.Eventhoughdatarecordingisanintegralfunctioninatypicaldataacquisition（数据采集）system,itisnotacrucialfunctioninafeedbackcontrolsystem.Forthisreason,weshallnotgointodetailsofdatarecordingdevicesinthisbook.Inamultiplemeasurementenvironment,amultiplexer（多路转换器）couldbeemployedpr

5、iortoorfollowingthesignal-conditioningprocess,inordertopickonemeasuredsignalatatimefromabankofdatachannelsforsubsequentprocessing.Inthismanner,oneunitofexpensiveprocessinghardwarecanbetime-shared（时刁｝复用）betweenseveralsignals.Sensor-transducer（传感器-变送器）devicesarepredominantly（主要的）analogcompon

6、entsthatgenerateanalogsignals,eventhoughdirectdigitaltransducersarebecomingincreasinglypopularindigitalcontrolapplications.Whenanalogtransducersareemployed,analog-to・digitalconverters（ADCs）havetobeusedtoconvertanalogsignalsintodigitaldatafordigitalcontrolThissignalmodificationprocessrequir

7、essamplingofanalogsignalsatdiscretetimepoints.Onceavalueissampled,itisencodedintoadigitalrepresentationsuchasstraightbinarycode,agraycode,binary-codedecimal（BCD）codeorAmericanStandardCodeforInformationInterchange（ASCII）.Thechangesinananalogsignalduetoitstransi