4.Graphiclanguages(version1996)

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1、4.Graphiclanguages(version1996)ThegraphiclanguagesdefinedinthisstandardareLD(LadderDiagram)andFBD(FunctionBlockDiagram).Thesequentialfunctionchart(SFC)elementsdefinedin2.6canbeusedinconjunctionwitheitheroftheselanguages.4.1CommonelementsTheelementsdefinedinthisclauseapplytobot

2、hthegraphiclanguagesintheStandard,thatis,LD(LadderDiagram)andFBD(FunctionBlockDiagram),andtothegraphicrepresentationofsequentialfunctionchart(SFC)elements.4.1.1RepresentationoflinesandblocksThegraphiclanguageelementsdefinedinthisclausearedrawnwithlineelementsusingcharactersfro

3、mtheISO/IEC646characterset,orusinggraphicorsemigraphicelements,asshownintable57.Linescanbeextendedbytheuseofconnectorsasshownintable57.Nostorageofdataorassociationwithdataelementsshallbeassociatedwiththeuseofconnectors;hence,toavoidambiguity,itshallbeanerroriftheidentifierused

4、asaconnectorlabelisthesameasthenameofanothernamedelementwithinthesameprogramorganizationunit.4.1.2DirectionofflowinnetworksAnetworkisdefinedasamaximalsetofinterconnectedgraphicelements,excludingtheleftandrightrailsinthecaseofnetworksintheLDlanguagedefinedin4.2.Provisionshallb

5、emadetoassociatewitheachnetworkorgroupofnetworksinagraphiclanguageanetworklabeldelimitedontherightbyacolon(:).Thislabelshallhavetheformofanidentifieroranunsigneddecimalintegerasdefinedinclause2ofthisPart.Thescopeofanetworkanditslabelshallbelocaltotheprogramorganizationunitin

6、whichthenetworkislocated.ExamplesofnetworksandnetworklabelsareshowninannexF.Graphiclanguagesareusedtorepresenttheflowofaconceptualquantitythroughoneormorenetworksrepresentingacontrolplan,thatis:-"Powerflow",analogoustotheflowofelectricpowerinanelectromechanicalrelaysystem,typi

7、callyusedinrelayladderdiagrams;-"Signalflow",analogoustotheflowofsignalsbetweenelementsofasignalprocessingsystem,typicallyusedinfunctionblockdiagrams;-"Activityflow",analogoustotheflowofcontrolbetweenelementsofanorganization,orbetweenthestepsofanelectromechanicalsequencer,typi

8、callyusedinsequentialfunctioncharts.Theappropriateconceptualq