plc控制的变频电梯系统的设计1.docx
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plc控制的变频电梯系统的设计1.docx
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plc控制的变频电梯系统的设计1
外文翻译
INDUSTRIALANDCOLLABORATIVECONTROLSYSTEMS
-ACOMPLEMENTARYSYMBIOSIS–
Lookingattoday’scontrolsystemonecanfindawidevarietyofimplementations.Frompureindustrialtocollaborativecontrolsystem(CCS)toolkitstohomegrownsystemsandanyvariationin-between.DecisionsonthetypeofimplementationshouldbedrivenbytechnicalargumentsRealityshowsthatfinancialandsociologicalreasonsformthecompletepicture.Anydecisionhasit’sadvantagesandit’sdrawbacks.Reliability,gooddocumentationandsupportareargumentsforindustrialcontrols.Financialargumentsdrivedecisionstowardscollaborativetools.Keepingthehandsonthesourcecodeandbeingabletosolveproblemsonyourownandfasterthanindustryaretheargumentforhomegrownsolutionsoropensourcesolutions.Theexperienceofmanyyearsofoperationsshowsthatwhichsolutionistheprimaryonedoesnotmatter,therearealwaysareaswhereatleastpartoftheotherimplementationsexist.Asaresultheterogeneoussystemshavetobemaintained.Thesupportfordifferentprotocolsisessential.Thispaperdescribesourexperiencewithindustrialcontrolsystems,PLCcontrolledturnkeysystems,theCCStoolkitEPICSandtheoperabilitybetweenallofthem.
FUNCTIONALITY
Theeverlastingquestionwhycontrolsystemsforacceleratorsandotherhighlyspecializedequipmentareoftenhomegrownoratleastdevelopedinacollaborationbutonlyinrarecasescommercialshallnotbeansweredhere.Wetrytosummarizeherebasicfunctionalitiesofdifferentcontrolsapproaches.
Front-endController
Oneofthecoreelementsofacontrolsystemisthefront-endcontroller.PLC’scanbeusedtoimplementmostofthefunctionstocontroltheequipment.Thedisadvantageisthecomplicatedaccesstothecontrolsproperties.ForinstanceallofthepropertiesofacontrolloopliketheP,IandDparameter,butalsothealarmlimitsandotheradditionalpropertiesmustbeaddressedindividuallyinordertoidentifytheminthecommunicationprotocolandlastnotleastinthedisplay-,alarm-andarchiveprograms.Inadditionanykindofmodificationsoftheseembeddedpropertiesisdifficulttotrackbecausetwoormoresystemsareinvolved.ThismightbeonestrongargumentwhycontrolloopsaremainlyimplementedontheIOClevelratherthanPLC’s.
I/OandControlLoops
ComplexcontrolalgorithmsandcontrolloopsarethedomainofDCSalikecontrolsystems.Thesupportforsetsofpredefineddisplayandcontrolspropertiesisessential.Ifnotalreadyavailable(likeinDCSsystems)suchsetsofgenericpropertiesaretypicallyspecifiedthroughoutacompletecontrolsystem(seenamespaces).
Sequence/Stateprograms
Sequenceprogramscanrunonanyprocessorinacontrolsystem.Theruntimeenvironmentdependsontherelevanceofthecodeforthecontrolsystem.Programsfulfillingwatchdogfunctionshavetorunonthefront-endprocessordirectly.Sequenceprogramsforcomplicatedstartupandshutdownprocedurescouldberunonaworkstationaswell.ThebasicfunctionalityofastatemachinecanbeevenimplementedinIEC61131.Codegeneratorscanproduce‘C’codewhichcanbecompiledfortheruntimeenvironment.
SupportedHardware
ThesupportforfieldbusesandEthernetbasedI/OisabasicfunctionalityforSCADAtypesystemsitiscommerciallyavailablefromanySCADAsystemonthemarket.Theintegrationofspecifichardwarewithspecificdriversanddataconversionisthehardpartinacommercialenvironment.OpenAPI’sorscriptingsupportsometimeshelptointegratecustomhardware.Ifthesetoolsarenotprovidedforthecontrolsystemitisdifficult–ifnotimpossible-tointegratecustomhardware.
NewindustrialstandardslikeOPCallowthecommunicationwithOPCawaredevicesandthecommunicationbetweencontrolsystems.Oneboundaryconditionforthiskindoffunctionalityistheunderlyingoperatingsystem.InthecaseofOPCitisboundtoDCOMwhichisaMicrosoftstandard.UNIXbasedcontrolsystemshaveahardtimetogetconnected.Onlycontrolsystemssupportingmultipleplatformscanplayamajorroleinaheterogeneousenvironments.
Asaresultthelimitedsupportforcustom-orspecializedhardwaremaygivereasonforthedevelopmentofanewcontrolsystem.
1.Graphic
Synopticdisplaysaretheadvertisingsignforanycontrolsystem.Commercialsynopticdisplayscomewitharichfunctionalityandlotsofspecialfeatures.Startingtomakeuseofallthesefeaturesonewillfindoutthatallindividualpropertiesofthegraphicobjectsmustbespecifiedindividually.SinceSCADAsystemsmustbegenerictheycannotforeseethataninputchanneldoesnotonlyconsistofavaluebutalsoconsistsofpropertieslikedisplayrangesandalarmvalues.Definingallofthesepropertiesagainandagaincanbeaprettyboringjob.Somesystemsallowtogenerateprototypesofgraphicobjects.Theseprototypeortemplategraphicsarecomplexandneedaspecialisttogeneratethem.
DCSorcustomsynopticdisplayprogramscanmakeuseofthecommonsetofpropertieseachI/Opointprovides.Thispredefinednamingschemewillfillinallstandardpropertyvaluesandthusonlyrequiretoentertherecord–ordevicenameintotheconfigurationtool.AclearadvantageforcontrolsystemswithanotionofI/OobjectsratherthanI/Opoints.
2.Alarming
Alarmsaregoodcandidatestodistinguishbetweendifferentcontrolsystemarchitectures.ThosesystemswhichhaveI/Oobjectimplementedalsoprovidealarmcheckingonthefront-endcomputer.ThosesystemswhichonlyknowaboutI/OpointshavetoaddalarmcheckingintotheI/Oprocessing.WhiletheI/Oobjectapproachallowstoimplementalarmcheckinginthenativeprogramminglanguageofthefront-endsystem,I/Opointorientedsystemstypicallyhavetoimplementthisfunctionalityintheirnativescriptinglanguage.Thisistypicallylessefficientanderrorpronebecauseallpropertiesmustbeindividuallyconfigured.Thisleadstoafloodofproperties.NotonlytheerrorstatesforeachI/OpointwinduptobeindividualI/OpointsbutalsothealarmlimitsandthealarmseverityofeachlimitmustbedefinedasI/Opointsifitisdesiredtobeabletochangetheirvaluesduringruntime.
BesidesthisimpactontheconfigurationsidetheprocessingandforwardingofalarmsmakesthedifferencebetweenSCADAandDCSsystems.SinceSCADAsystemsinherentlydonot‘know’aboutalarms,eachalarmstatemustbepolledeitherdirectlyfromtheclientapplicationorinadvancedcasesfromaneventmanagerwhichwillforwardalarmstatestotheclients.Inanycasealotofoverheadfor‘just’checkingalarmlimits.DCSsystemagainhavetheadvantagethatclientscaneitherregisterthemselvesforalarmstatesundthusgettheinformationforwardedorareconfiguredtosendalarmchangestocertaindestinationsspreadaroundthecontrolsystem.Thelattercaseisonlypossibleforsystemswhichintotalareconfiguredwithallthenodestakingpartinthecontrolsnetwork.
3.TrendingandArchiving
Trendinghasbecomeanimportantbusinessincontrolsystemsarchitectures.Trendsarenecessarytotraceerrorconditionsorforpostmortemandperformanceanalysisofthecontrolledplant.Besidessomecustomimplementationswhicharecapabletostorethedataofcompletecontrolobjects,mostofthetrendingtoolsarchivescalardata.Additionalfeatureslikeconditionaltrendingorcorrelationplotsmakeupthedifferencebetweenindividualimplementations.
4.ProgrammingInterfaces
WithrespecttoopenprogramminginterfacesPLC’sandDCSsystemshaveacommonstrategy.Theyarerunningreliablybecausethere’snowaytointegratecustomcodewhichcouldinterferewiththeinternalprocessing.Asaconsequencethecustomerhastoorder‘specials’-whichareextremelyexpensive–orforgetaboutitandusethesystemasablackbox.
SinceSCADAsystemsbydefinitionmustbeabletocommunicatewithavarietyofI/OsubsystemstheyalreadyhavesomebuiltinAPI’swhichallowtointegratecustomfunctionality.
Speciallycollaborativesystemsneedacertainopennesstofulfillalltherequirementsfromvariousdevelopmentgroups.Programminginterfacesonalllevelslikefont-endI/O,front-endprocessing,networkingetc.aremandatory.Aclearadvantageforthistypeofsystem.
5.Redundancy
IfredundancymeanstheseamlessswitchwhichtakesoverallthestatesandallthevaluesoftheI/Oandallstatesofallprogramscurrentlyrunning,itisadomainofonlyafewDCSsystems.CustomorCCSimplementationdonotprovidethiskindoffunctionality.Maybebecauseoftheimmenseeffortandthefactthatitisonlyrequiredinrarecases.
Besidesprocessorredundancy,redundantnetworksorI/OsubsystemsareavailableforcertaincommercialDCSsystems.Again–adomainwhichisnotcoveredbySCADAorCCSimplementations.
CONCLUSIONS
Dependingonthesizeandtherequirementsforacontrolsprojectthecombinationofcommercialsolutionsandsolutionsbasedonacollaborativeapproachispossibleinanyratebetween0and100percent.Thisappliesforalllevelsfromimplementationtolongtermsupport.Specialrequirementsonsafetyissuesoralackofmanpowermightturnthescalecommercial.Thenecessitytointerfacespecialhardware,specialtimingrequirements,the‘havingthecodeinmyhands’argumentortheinitialcostsforcommercialsolutionswillturnthescalecollaborative.AslongascollaborativeapproacheslikeEPICSstayuptodateandrunasstableandrobustascommercialsolutions,bothwillkeeptheirpositioninthecontrolsworldinacomplementarysymbiosis.
工业控制系统和协同控制系统
当今的控制系统被广泛运用于许多领域。
从单纯的工业控制系统到协同控制系统(CCS),控制系统不停变化,不断升级,现在则趋向于家庭控制系统,而它则是这两者的变种。
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- plc 控制 变频 电梯 系统 设计