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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.Automaticprocesscontrolisconcernedwithmaintainin
2、gprocessvariablestemperaturespressuresflowscompositions,andthelikeatsomedesiredoperationvalue.Processesaredynamicinnature.Changesarealwaysoccurring,andifactionsarenottaken,theimportantprocessvariables-thoserelatedtosafety,productquality,andproductionrates-willnotachievedesignconditions.Inorderto
3、fixideas,letusconsideraheatexchangerinwhichaprocessstreamisheatedbycondensingsteam.TheprocessissketchedinFig.1Fig.1HeatexchangerThepurposeofthisunitistoheattheprocessfluidfromsomeinlettemperature,Ti(t),uptoacertaindesiredoutlettemperature,T(t).Asmentioned,theheatingmediumiscondensingsteam.Theene
4、rgygainedbytheprocessfluidisequaltotheheatreleasedbythesteam,providedtherearenoheatlossestosurroundings,iiithatis,theheatexchangerandpipingarewellinsulated.Inthisprocesstherearemanyvariablesthatcanchange,causingtheoutlettemperaturetodeviatefromitsdesiredvalue.[21Ifthishappens,someactionmustbetak
5、entocorrectforthisdeviation.Thatis,theobjectiveistocontroltheoutletprocesstemperaturetomaintainitsdesiredvalue.OnewaytoaccomplishthisobjectiveisbyfirstmeasuringthetemperatureT(t),thencomparingittoitsdesiredvalue,and,basedonthiscomparison,decidingwhattodotocorrectforanydeviation.Theflowofsteamcan
6、beusedtocorrectforthedeviation.Thisis,ifthetemperatureisaboveitsdesiredvalue,thenthesteamvalvecanbethrottledbacktocutthestearrflow(energy)totheheatexchanger.Ifthetemperatureisbelowitsdesiredvalue,thenthesteamvalvecouldbeopenedsomemoretoincreasethesteamflow(energy)totheexchanger.Allofthesecanbedo
7、nemanuallybytheoperator,andsincetheprocedureisfairlystraightforward,itshouldpresentnoproblem.However,sinceinmostprocessplantstherearehundredsofvariablesthatmustbemaintainedatsomedesiredvalue,thiscorrectionprocedurewouldrequi
