What is the difference and common between DCS and PLCDCS与PLC的区别和共通

WhatisthedifferenceandcommonbetweenDCSandPLC（DCS与PLC的区别和共通）

DCSisadistributedcontrolsystem,isasystem,ratherthanaspecificdevice,communicationbetweendevicesisoneoftheirownmaking,usingtheadvantagesoflargeinternationalcompaniestodeveloptheirownOEMproducts,isclosed,tobereplaced,onlytofindthemtobeextended.Therehasbeennoclimatethathasbeensupersededbyfieldbus.

PLCreferstoacontroldevice,

ThedifferencesandsimilaritiesbetweenDCSandPLC[585]

Controlproductsarenumerousandvarious.ThecommonlyusedcontrolproductsincludeDCS,PLC,andtwomajorcategories.WeextendedtheconceptofDCStoFCS.

DCS(DistributedContorlSystem),distributedcontrolsystem,alsocalleddistributedcontrolsystem.

PLC(Program,Logic,Control)programmablelogiccontroller.

FCS(FieldBus,Contorl,Syestem)fieldbuscontrolsystem

Untilnow,thereisnostrictboundarybetweenDCSandPLC.Formostpeople,thebigsystemisDCS,andthesmallsystemiscalledPLC.Ofcourse,itisnotimpossibletosayso,butitisnotright.Nowlet'sre-establishthisidea.

Well,firstofall,what'sthedifferencebetweenDCSandPLC?

1,intermsofdevelopment:

DCSevolvedfromthetraditionaldashboardmonitoringsystem.Therefore,controlofDCSfromcongenitalitlaysmoreemphasisontheinstrument,suchastheYOKOGAWACS3000DCSsystemweuseornolimittothenumberofPID(PID,PIDalgorithmisthecontrolvalve,numberofstandardalgorithm,thePIDinverterclosed-loopcontrolusuallydeterminesthenumberofadjustablevalve).

PLCevolvedfromtraditionalrelayloops,andtheinitialPLCdidnotevenhavetheanalogprocessingcapability,soPLCstartedbyemphasizinglogicalcomputingcapabilities.

2,fromtheaspectsofsystemscalabilityandcompatibility:

Marketcontrolproductsarenumerous,regardlessofDCSorPLC,therearemanymanufacturersintheproductionandsale.ForPLCsystems,thereisgenerallynoorverylittleneedforextensions,becausePLCsystemsaregenerallyusedfordevices.Generallyspeaking,PLChasveryfewcompatibilityrequirements.Forexample,twoormoresystemsrequireresourcesharing,whichisdifficultforPLC.Moreover,PLCusuallyusesadedicatednetworkstructure,suchasSIEMENS'sMPItotallinearnetwork,andevenanoperatorstationisnoteasyorexpensive.

DCSintheprocessofdevelopmentisthemanufacturersownsystem,butmostoftheDCSsystem,suchasHengheYOKOGAWA,HoneWeil,ABBandsoon,althoughtheinternalsystem(process)communicationprotocolisnotthesame,buttheoperationallevelnetworkplatforminvariablychosetheEthernetnetwork,usingstandardordeformationoftheTCP/IPprotocol.Thisprovidesaveryconvenientscalability.Inthisnetwork,thecontrollerandthecomputerallexistasanode.Aslongasthenetworkarrives,thenumberofnodesandthelocationofnodescanbechangedatwill.Inaddition,basedonwindows,OPC,DDEandotheropenprotocols,thesystemcanalsobeveryconvenientcommunication,inordertoachieveresourcesharing.

3,fromthedatabase:

DCSgenerallyprovidesaunifieddatabase.Inotherwords,inaDCSsystem,onceadataispresentinthedatabase,itcanbereferencedinanycase,suchasinconfigurationsoftware,inmonitoringsoftware,inatrenddiagram,inareport......ThedatabaseofPLCsystemisusuallynotunified,configurationsoftwareandmonitoringsoftware,andevenarchivingsoftware,havetheirowndatabase.WhydoyouoftensaythatSIEMENS'sS7400tomorethan414beforeitiscalledDCS?BecauseSIEMENS'sPCS7systemusesaunifieddatabase,thePCS7requirescontrollerstobeatleastS7414-3ormore.

4,fromthetimescheduling:

PLCprogramsgenerallydonotruninapredeterminedcycle.ThePLCprogramisexecutedfromstarttofinishandthenfromscratch.(nowsomeofthenewPLChasimproved,buttherearelimitstothenumberoftaskscycles),andtheDCScansetthetaskcycle.Forexample,quicktasks,etc..Thesameisthesensorsampling,thepressuresensorchangetimeisveryshort,wecanusethe200mstaskcyclesampling,andthetemperaturesensorlagtimeisverybig,wemayusethe2Sdutycycletosample.Inthisway,DCScanreasonablycontrolthecontroller'sresources.

5,fromthenetworkstructureforbaking:

Generallyspeaking,DCSusedtwolayernetworkstructure,alayerfortheprocesslevelnetwork,mostoftheDCSbusprotocolusingtheirown,suchasHenghe'sModbus,SIEMENSandABBProfibus,ABBCANbus,theseprotocolsarebasedonthestandardserialRS232protocolorRS485protocol.TheIOmodule,especiallythesampleddataanalog(machinecode,213/scancycle)isverylarge,thesceneatthesametimemanyinterferingfactors,thereforeshouldbeusedinhighthroughputandstronganti-interferenceabilityofthenetworkstandard.ThebusstructurebasedonRS485serialasynchronouscommunicationmodemeetstherequirementsoffieldcommunication.

ThesampleddataofIOisconvertedintoplasticdataorsoliddataafterCPUconversion,anditistransmittedontheoperationlevelnetwork(secondlayernetwork).Therefore,theoperationlevelnetworkcanadoptthenetworkstandardwithmoderatedatathroughput,fasttransmissionspeedandconvenientconnection.Atthesametime,becausetheoperationlevelnetworkisgenerallyarrangedinthecontrolroom,therequirementofanti-jammingisrelativelylow.Therefore,adoptingstandardEthernetisthebestchoice.TCP/IPprotocolisastandardEthernetprotocol,generallyweuse100Mbit/scommunicationspeed.

ThetaskofPLCsystemisrelativelysimple,sotheamountofdatatobetransmittedwillnotbetoolarge,sothecommonPLCsystemisanetworkstructure.Theprocesslevelnetworkandtheoperationlevelnetworkaremergedtogether,ortheprocesslevelnetworksimplifiestheinternalconnectionbetweenmodules.PLCwillnotorrarelyuseethernet.

6,fromthesizeoftheapplicationobject:

PLCisgenerallyusedinsmallautomaticcontrolareas,suchasequipmentcontrolorasmallamountofanalogcontrolandinterlocking,whilelarge-scaleapplicationsaregenerallyDCS.Ofcourse,thisconceptisnotaccurate,butveryintuitive,andweusedtocallthesystemlargerthan600pointsDCS,smallerthanthisscalecalledPLC.OurheatpumpandQCS,horizontalproductssupportingthecontrolsystemisgenerallyreferredtoasPLC.

Thedifference,saidsomanyPLCandDCS,butweshouldbeawarethatthePLCandDCSdevelopmenttoday,infactinthemovetowardeachother,strictlyspeaking,PLCandDCSnowhasnotaknifecut,alotofthetimebetweenconceptshavebeenblurred.Now,let'stalkaboutthesimilarities.

1,fromthefunction:

PLCalreadyhasanalogcontrolcapabilities,andsomePLCsystemsareevenpowerfulanalogprocessingcapabilities,suchasHenghe,FA-MA3,SIEMENS'sS7400,ABB'sControl,Logix,andSchneider'sQuantumsystem.AndDCSalsohasprettystronglogicprocessingcapabilities,suchastheimplementationofalltheprocessinterlockinganddevicelinkagewecanuseonCS3000.

2,fromthesystemstructure:

ThebasicstructureofPLCandDCSisthesame.PLCdevelopmenttotoday,hasbeenfullytransplantedtothecomputersystemcontrol,thetraditionalprogrammerhaslongbeeneliminated.SmallapplicationsPLCgenerallyusetouch-screen,large-scaleapplicationsofPLC,thefulluseofcomputersystems.SameasDCS,

IOcontrollerandfieldbusstation(usuallybusRS485orRS232asynchronousserialcommunicationprotocolbasedon),ifthereisnoextensionbetweenthecontrollerandcomputerrequirements,aswellastheuseofacomputercase,willalsousethebuscommunication.Butifmorethanonecomputerisused,thesystemstructurewillbethesameasDCS,andtheuppercomputerplatformusestheEthernetarchitecture.Thisisoneofthereasonswhytheconceptoflarge-scalePLCandDCSisblurred.

3,thedevelopmentdirectionofPLCandDCS:

TheminiaturizationofPLCwillbedevelopedtomorespecializedapplications,suchasmoretargetedfeatures,moretargetedapplicationsenvironment,andsoon.TheboundariesoflargePLCandDCSaregraduallydiluteduntilfullyintegrated.

DCSwillcontinuetodevelopinthedirectionofFCS.ThecoreoftheFCSisespeciallyimportantinadditiontothedecentralizedcontrolsystem.TheapplicationofFCSinforeigncountrieshasdevelopedtoinstrumentlevel.Thecontrolsystemwithonlysignalacquisitionandprovidetheman-machineinterfaceandcontrollogic,theanalogcontrolinthefieldofinstrument,withoutthetraditionalcableconnectionbetweentheinstrumentandcontrolsystem,fieldbusisusedtoconnectthewholeinstrumentsystem.(atpresent,HenghehasusedFCSintheCNOOCShellpetrochemicalproject,andtheinstrumentleveladoptsintelligentinstruments,suchasEJXandsoon.Ithastheworld'smostadvancedcontrollevel).

HowdoyoutreatPLCandDCScorrectly?

Personally,IneverstressedthedifferencebetweenPLCandDCS,andIusedthemasanewterm,"controlproducts."".Weprovideuserswiththemostsuitableusercontrolsystem.MostusersdonotwanttouseDCSbecausetheywanttouseaDCS,andcontrolproductsmustbepositionedonthebasisofmeetingtheuser'sprocessrequirements.Infact,userswhouseDCSorPLCmostlyhavenevercomeintocontactwithautomaticcontrolproductsorhavesomespecialneeds.Puttingtoomuchemphasisonthisstuffwillonlyleadtoarguments.

FromthedifferenceandcommongroundbetweenPLCandDCS,weunderstandthegeneralsituationofcontrolproducts.Notethatasprofessionals,wedonotfortheproductunderthedefinitionofPLCorDCS,andtheirownpsychologicalproductscannotbetreateddifferently.

Conceptually,PLCandDCSarenotoriginallyalogicallayerofconcepts,andtheycanbeseenfromnames:PLCisnamedafterfunction,andDCSisnamedafterarchitecture.PLCcanmakeupDCS!Ofcourse,performancedifferencesstillexist,butlookattheproductsandneeds.Fromtheapplicationpointofview,simplytoPLC,DCStodistinguishbetween,oftenintothemisunderstanding.

ThedifferencebetweenDCScontrolsystemandPLCcontrol

1.DCSisadecentralizedcontrolsystem,andPLCisjustaprogrammablecontrollerthatcontrolsthe"device",whichisthedifferencebetween"system"and"device".Thesystemcanrealizethefunctionandcoordinationofanydevice,andthePLCdeviceonlyimplementsthefunctionofthisunit

2.inthenetwork,theDCSnetworkisthecentralnervoussystem,theMACSsystemofHollysyscorporationsysteminthenetworkusingtheindustrialEthernetisthedualredundant100Mbps,usingtheinternationalstandardprotocolTCP/IP.Itisasafeandreliablehigh-speedcommunicationnetworkredundancy,systemdevelopmentandopenness.AndbetterPLCbecausebasicallyforindividualwork,itscommunicationswithotherPLCorPC,thebasicformofthenetworkisasinglenetworkstructure,networkprotocolsareofteninconsistentwithinternationalstandards.Innetworksecurity,PLCdoesnothaveverygoodprotectionmeasures.Weusepower,CPU,andnetworkdualredundancy

Thewholeschemeconsidered3.DCS,withengineerstationoperatorstation,betweenthestationandthestationintherunningprogramafterdownloadingisatightjointrelationship,anystation,anyfunction,anycontrolleddeviceareinterlockedcontrol,coordinatedcontrol;andsinglePLCcomposedofinterconnectedsystem,

Theconnectionbetweenthestationandthestation(PLCandPLC)isalooseconnection,anditcannotdothefunctionofcoordinatedcontrol.

4.DCSinthewholedesignonalotofthescalabilityoftheinterface,theexternalsystemortheextensionofthesystemisveryconvenient,completethewholesystemPLCthelap,toarbitrarilyincreaseordecreasetheoperatorstationisdifficulttoachieve.

5.:toensurethesafetyofDCSDCScontrolequipmentissafeandreliable,DCSusesadualredundantcontrolunit,asanimportantcontrolunitwhenafaultoccurs,therewillberedundanttotherelevantunitofreal-timeswitchwithoutdisturbancetotheunitofwork,toensurethesafetyandreliabilityofthewholesystem.ThereisnoredundancyconceptinPLClappingsystem,letaloneredundantcontrolstrategy.EspeciallywhenaPLCunitfails,ithastostopthewholesystembeforereplacing,maintaining,andreprogramming.SotheDCSsystemisonelevelaboveitssecurityandreliability.

6.systemsoftware,toupdatethecontrolschemeofvarioustechnologyisabasicfunctionoftheDCS,whenaprogramchanges,engineersonlyneedtoengineerstationadmiralchangedprogramcompiled,executedunderthecommandofit,thedownloadingprocessisfinishedautomaticallybythesystem,doesnotaffecttheoriginalcontrolschemeoperation.Variouscontrolsoftwareandalgorithmofthesystemcanimprovethecontrolprecisionofprocesscontrolobject.AsfortheformofthePLCsystem,theworkloadisextremelylarge,firstneedtodeterminetheeditandupdateofwhatPLCis,andthenusethecorrespondingcompilercompiler,thenadedicatedmachine(Reader)specialoneoftheprocedureswillbetransmittedtothePLC,inthesystemcommissioningperiod,alargenumberofincreasethetimeandcostofdebugginganddebugging,veryconducivetomaintenanceafter.Thereisagreatdifferenceincontrolaccuracy.Thisdetermineswhythelargeandmedium-sizedcontrolprojects(morethan500points),basicallydonotuseallconnectedbythePLCsystem.

7.modules:DCSsystem,allI/OmodulesareCPU,youcanachievetheacquisitionandoutputsignalqualityjudgmentandscalarconversion,fault,liveplugandplay,randomreplacement.ThePLCmoduleisonlyasimpleelectricalconversionunit,thereisnosmartchip,afterthefailureofthecorrespond