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1、TECHNICALREPORTISA–TR12.2–1995IntrinsicallySafeSystemAssessmentUsingtheEntityConceptApproved2January1995TMISATheInstrumentation,–Systems,andAutomationSocietyISATR12.21995,IntrinsicallySafeSystemAssessmentUsingtheEntityConceptISBN:1-55617-559-0Copyright©1995bytheInstrumentSocietyofAmerica.A
2、llrightsreserved.PrintedintheUnitedStatesofAmerica.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans(electronic,mechanical,photocopying,recording,orotherwise),withoutthepriorwrittenpermissionofthepublisher.ISA67AlexanderDriveP.O.Box12277Rese
3、archTrianglePark,NorthCarolina27709PrefaceThisprefaceisincludedforinformationalpurposesandisnotpartofISA-TR12.2-1995.ThistechnicalreporthasbeenpreparedaspartoftheserviceofISA,theinternationalsocietyformeasurementandcontrol,towardagoalofuniformityinthefieldofinstrumentation.Tobeofrealvalue,
4、thisdocumentshouldnotbestatic,butshouldbesubjecttoperiodicreview.Towardthisend,theSocietywelcomesallcommentsandcriticisms,andasksthattheybeaddressedtotheSecretary,StandardsandPracticesBoard,InternationalSocietyforMeasurementandControl,67AlexanderDrive,P.O.Box12277,ResearchTrianglePark,NC27
5、709,Telephone(919)990-9227,Fax(919)549-8288,e-mail:standards@isa.org.TheISAStandardsandPracticesDepartmentisawareofthegrowingneedforattentiontothemetricsystemofunitsingeneral,andtheInternationalSystemofUnits(SI)inparticular,inthepreparationofinstrumentationstandards,recommendedpractices,an
6、dtechnicalreports.TheDepartmentisfurtherawareofthebenefitstoU.S.A.usersofISAstandardsofincorporatingsuitablereferencestotheSI(andthemetricsystem)intheirbusinessandprofessionaldealingswithothercountries.Towardthisend,thisDepartmentwillendeavortointroduceSI-acceptablemetricunitsinallnewandre
7、visedstandardstothegreatestextentpossible.TheMetricPracticeGuide,whichhasbeenpublishedbytheInstituteofElectricalandElectronicsEngineersasANSI/IEEEStd.268-1992,andfuturerevisions,willbethereferenceguidefordefinitions,symbols,abbreviations,andconversionfactors.I
