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1、河北建筑工程学院毕业设计(论文)外文资料翻译系别:电气工程系专业:电气工程及其自动化班级:姓名:学号:外文出处:SpecializedEnglishForArchitecturalElectricEngineeringandAutomation附件:1、外文原文;2、外文资料翻译译文。指导教师评语:签字:年月日注:请将该封面与附件装订成册。1、外文原文IntroductionstotemperaturecontrolandPIDcontrollersProcesscontrolsystem.Automaticprocesscontrolisconcernedwit
2、hmaintainingprocessvariablestemperaturespressuresflowscompositions,andthelikeatsomedesiredoperationvalue.Processesaredynamicinnature.Changesarealwaysoccurring,andifactionsarenottaken,theimportantprocessvariables-thoserelatedtosafety,productquality,andproductionrates-willnotachievedesi
3、gnconditions.Inordertofixideas,letusconsideraheatexchangerinwhichaprocessstreamisheatedbycondensingsteam.TheprocessissketchedinFig.1Fig.1HeatexchangerThepurposeofthisunitistoheattheprocessfluidfromsomeinlettemperature,Ti(t),uptoacertaindesiredoutlettemperature,T(t).Asmentioned,theheat
4、ingmediumiscondensingsteam.Theenergygainedbytheprocessfluidisequaltotheheatreleasedbythesteam,providedtherearenoheatlossestosurroundings,iiithatis,theheatexchangerandpipingarewellinsulated.Inthisprocesstherearemanyvariablesthatcanchange,causingtheoutlettemperaturetodeviatefromitsdesir
5、edvalue.[21Ifthishappens,someactionmustbetakentocorrectforthisdeviation.Thatis,theobjectiveistocontroltheoutletprocesstemperaturetomaintainitsdesiredvalue.OnewaytoaccomplishthisobjectiveisbyfirstmeasuringthetemperatureT(t),thencomparingittoitsdesiredvalue,and,basedonthiscomparison,dec
6、idingwhattodotocorrectforanydeviation.Theflowofsteamcanbeusedtocorrectforthedeviation.Thisis,ifthetemperatureisaboveitsdesiredvalue,thenthesteamvalvecanbethrottledbacktocutthestearrflow(energy)totheheatexchanger.Ifthetemperatureisbelowitsdesiredvalue,thenthesteamvalvecouldbeopenedsome
7、moretoincreasethesteamflow(energy)totheexchanger.Allofthesecanbedonemanuallybytheoperator,andsincetheprocedureisfairlystraightforward,itshouldpresentnoproblem.However,sinceinmostprocessplantstherearehundredsofvariablesthatmustbemaintainedatsomedesiredvalue,thiscorrectionprocedurewould
8、requi