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1、STANDARDISA-5.4-1991FormerlyANSI/ISA-5.4-1991InstrumentLoopDiagramsApproved9September1991TMISATheInstrumentation,–Systems,andAutomationSocietyISA-5.4-1991InstrumentLoopDiagramsISBN1-55617-227-3Copyright1991bytheInstrumentSocietyofAmerica.Allrightsreserved.PrintedintheUnitedStat
2、esofAmerica.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans(electronic,mechanical,photocopying,recording,orotherwise),withoutthepriorwrittenpermissionofthepublisher.ISA67AlexanderDriveP.O.Box12277ResearchTrianglePark,NorthCaroli
3、na27709PrefaceTheinformationcontainedinthePrefaceandForwardisforinformationonlyandisnotapartofthestandard.ThisstandardispreparedaspartoftheserviceofISAtowardagoalofuniformityinthefieldofinstrumentation.Tobeofrealvalue,thisdocumentshouldnotbestatic,butmustbesubjecttoperiodicrevie
4、w.Towardthisend,theSocietywelcomesallcommentsandcriticisms,andrequestthattheybeaddressedtotheSecretary,StandardsandPracticesBoard,ISA,67AlexanderDrive,P.O.Box12277,ResearchTrianglePark,NC27709.Telephone(919)549-8411,e-mail:standards@isa.org.TheISAStandardsandPracticesDepartmenti
5、sawareofthegrowingneedforattentiontothemetricsystemofunitsingeneralandtheInternationalSystemofUnits(SI)inparticular,inthepreparationofinstrumentationstandards.TheDepartmentisfurtherawareofthebenefitstoU.S.A.usersofISAstandardsofincorporatingsuitablereferencestotheSI(andthemetric
6、system)intheirbusinessandprofessionaldealingswithothercountries.Towardthisend,thisDepartmentwilltrytointroduceSI-acceptablemetricunitsinallnewandrevisedstandardstothegreatestextentpossible.TheMetricPracticeGuide,publishedbytheInstituteofElectricalandElectronicsEngineersasANSI/IE
7、EEStd.268-1982,andfuturerevisionswillbethereferenceguidefordefinitions,symbols,abbreviations,andconversionfactors.ItisthepolicyofISAtoencourageandwelcometheparticipationofallconcernedindividualsandinterestsinthedevelopmentofISAstandards.ParticipationintheISAstandards-makingproce
8、ssbyanindividualinnowayconstitutesendorsementby
