建筑电气英文论文文档格式.docx
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-INTRODUCTION
ProcesscontrolsingeneralstartedatDESYintheearly80thwiththeinstallationofthecryogeniccontrolsystemfortheacceleratorHERA(Hadron-Elektron-Ring-Anlage).Anewtechnologywasnecessarybecausetheexistinghardwarewasnotcapabletohandlestandardprocesscontrolssignalslike4to20mAinputandoutputsignalsandthesoftwarewasnotdesignedtorunPIDcontrolloopsatastablerepetitionrateof0.1seconds.Inadditionsequenceprogramswerenecessarytoimplementstartupandshutdownproceduresforthecomplexcryogenicprocesseslikecoldboxesandcompetecompressorstreets.
Soonitwasnecessarytoaddinterfacestofieldbusesandtoaddcomputingpowertocryogeniccontrols.SincetheinstalledD/3system[1]onlyprovidedandocumentedserialconnectiononamultibusboard,thedecisionwasmadetoimplementaDMAconnectiontoVMEandtoemulatethemultibusboard’sfunctionality.ThenecessarycomputingpowerfortemperatureconversionscamefromaMotorolaMVME167CPUandthefieldbusadaptertotheinhouseSEDACfieldbuswasrunningonanadditionalMVME162.TheoperatingsystemwasVxWorksandtheapplicationwastheEPICStoolkit.
SincethisimplementationwassuccessfulitwasalsoimplementedfortheutilitycontrolswhichwerelookingforagenericsolutiontosupervisetheirdistributedPLC’s.
ASELECTIONOFPROCESSCONTROLSYSTEMSATDESY
DCS(D/3)
AsaresultofamarketsurveytheD/3systemfromGSEwasselectedfortheHERAcryogenicplant.ThedecisionwasfortunatebecauseoftheDCScharacteroftheD/3.Thepossibilitytoexpandthesystemonthedisplay-andontheI/OsidehelpedtosolvetheincreasingcontroldemandsforHERA.ThelimitingfactorforthesizeofthesystemisnotthetotalnumberofI/Obutthetrafficonthecommunicationnetwork.Thistrafficisdeterminedbythetotalamountofarchiveddatanotbythedataconfiguredinthealarmsystem.Thetechnicalbackgroundofthislimitationisthefactthatarchiveddataarepolledfromthedisplayserverswhereasthealarmsarepushedtoconfigureddestinationslikealarm-files,(printer)queuesordisplays.
SCADASystemswithDCSFeatures(Cube)
ThefactthattheD/3systemmentionedabovehadsomehardcodedlimitationswithrespecttotheY2Kproblemwasforcingustolookforanupgradeorareplacementoftheexistingsystem.AsaresultofacallfortenderthecompanyOrsiwiththeirproductCubecameintoplay[2].Theprojectincludedacompletereplacementoftheinstalledfunctionality.ThisincludedtheD/3aswellastheintegrationoftheDESYfieldbusSEDACandthetemperatureconversioninVME.Theprojectstartedpromising.Butsoontechnicalandorganizationalproblemswerepushingthescheduletoit’slimitswhichweredeterminedbytheHERAshutdownscheduledatthattime.Thefinalacceptancetestatthevendorssiteshoweddramaticperformanceproblems.Twofactorscouldbeidentifiedasthecauseoftheseproblems.ThefirstonewasrelatedtotheunderestimatedCPUloadofthe6thgradepolynomialtemperatureconversionrunningat1Hz.ThesecondonewastheadditionalCPUloadcausedbythecomplexfunctionalityoftheexistingD/3system.Hereitwasunderestimatedthateachdigitalandanaloginputandoutputchannelhadit’sownalarmlimitsintheD/3system.InaSCADAlikesystemasCubethebasefunctionalityofachannelistoreadthevalueandmakeitavailabletothesystem.Anyadditionalfunctionalitymustbeadded.Lastnotleasttheloadonthenetworkforpollingallthealarmlimits–typicallyforaSCADAsystem–wasalsodrivingthenetworktoit’slimits.
FinallythecontractwithOrsiwascancelledandanupgradeoftheD/3systemwastheonlypossiblesolution.Itwasfinallycarriedoutinmarch2003.
InanycaseitshouldbementionedthattheCubeapproachhadtheadvantageofahomogeneousconfigurationenvironment(fortheCubefrontendcontrollers)–comparedwithheterogeneousenvironmentsfor‘pure’SCADAsystems.
SCADA(PVSS-II)
TheH1experimentattheHERAacceleratordecidedtousePVSS-IIforanupgradeoftheirslowcontrolsystems[3].TheexistingsystemsweredevelopedbyseveralmembersoftheH1collaborationandweredifficulttomaintain.ThedecisiontousePVSSasareplacementwasdrivenbytheresultsofanextensivesurveycarriedoutatCERNbytheJointControlsProject[4].PVSSisa‘pure’SupervisoryAndDataAcquisitionSystem(SCADA).ItprovidesasetofdriversforseveralfieldbusesandgenericsocketlibrariestoimplementcommunicationoverTCP/IP.Thecoreelementisthesocalledeventmanager.Itcollectsthedata(mostlybypolling)fromtheI/Odevicesandprovidesaneventservicetotheattachedmanagementserviceslike:
controlmanager,databasemanager,userinterface,APImanagerandthebuiltinHTTPserver.ThePVSSscriptinglibraryallowstoimplementcomplexsequencesaswellascomplexgraphics.ComparedwithotherSCADAsystemsPVSScomeswithonebasicfeature:
itprovidesatrueobjectorientedAPItothedevice’sdata.
OnemajordisadvantageofSCADAsystemsisthefactthattwodatabases,theoneforthePLCandtheonefortheSCADAsystemmustbemaintained.Integratedenvironmentstrytoovercomethisrestriction.
EPICS
EPICShasemergedatDESYfromaproblemsolvertoafullyintegratedcontrolsystem.Startingfromthedatacollectorandnumbercruncherforthecryogeniccontrolsystem,EPICSmadeit’swaytobecomethecoreapplicationfortheDESYutilitygroup.InadditionitisusedwhereverdataisavailablethroughVMEboardsorbymeansofIndustryPack(IP)modules.ForthosecryogenicsystemswhicharenotcontrolledbytheD/3systemEPICSisusedwithit’scompletefunctionality.Intotalabout50InputOutputController(IOC)areoperationalprocessingabout25thousandrecords.
1EPICSasaSCADASystem
Theutilitygroup(water,electricalpower,compressedair,heatingandairconditioning)isusingavarietyofPLC’sspreadoutoverthewholeDESYsite.EPICSisusedtocollectthedatafromthesePLC’soverProfibus(FMSandDP)andoverEthernet(SiemensH1andTCP).TheIOC’sprovidetheinterfacestothebusesandcollectthedata.ThebuiltinalarmcheckingoftheEPICSrecordsisusedtostoreandforwardalarmstatestothealarmhandler(alh)oftheEPICStoolkit.Inadditiontoolslikethechannelarchiverandthegraphicdisplay(dm2k)areused.Thedefaultnameresolution(byUDPbroadcast)andthedirectoryserver(nameserver)areusedtoconnect
clientandserverapplicationsoverTCP.AllofthesearebasicallySCADAfunctions.
Thetextualrepresentationofallconfigurationfiles(fortheIOC,thegraphictool,thealarmhandlerandthearchiver)providesaflexibleconfigurationscheme.AtDESYtheutilitygrouphasdevelopedasetoftoolstocreateIOCdatabasesandalarmconfigurationfilesfromOracle.ThiswaythecontrolsgroupprovidestheservicetomaintaintheEPICStoolsandtheIOC’swhiletheuserscanconcentrateontheequipmentbeingcontrolled.
2EPICSasaDCSSystem
BesidesthebasiccomponentsofaSCADAsystemEPICSalsoprovidesafullflavouredInputOutputController(IOC).TheIOCprovidesallofthefunctionaDCSsystemrequires,suchas:
astandardsetofpropertiesimplementedineachrecord,builtinalarmcheckingprocessedduringtheexecutionofeachrecord;
controlrecordslikePIDetc.;
configurationtoolsfortheprocessingengine.TheflexiblenamingschemeandthedefaultdisplayandalarmpropertiesforeachrecordeasetheconnectionbetweentheoperatortoolsandtheIOC’s.Theflexibledataacquisitionsupportsthepollmodeaswellasthepublishsubscribemode.Thelatterreducesthetrafficdrastically.
PLC’s
PLC’sprovidenowadaysthesamerichfunctionalityasitwasknownfromstandalonecontrolsystemsinthepast.BesidesthebasicfeaturesliketheperiodicexecutionofadefinedsetoffunctionstheyalsoallowextensivecommunicationoverEthernetincludingembeddedhttpserversanddifferentsetsofcommunicationprograms.Besidesthecommunicationprocessors,displayprocessorscanbelinkedtoPLC’stoprovidelocaldisplayswhichcanbecomprisedastouchpanelsforoperatorinterventionandvaluesettings.
ThesekindofPLC’sareattractiveforturnkeysystemswhicharecommissionedatthevendorssiteandlaterintegratedintothecustomerscontrolsystem.
IntelligentI/O
NewdevelopmentsinI/Odevicesallowto‘cluster’I/Oinevensmallergroupsand