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基于OPCDA3.0规范的客户端在Delphi下的设计与实现
Introduction
OPC(OLEforProcessControl)isastandardfordataexchangebetweendifferentdevicesinindustrialautomation.OPCDA(DataAccess)isonepartofthisstandard,whichdefineshowtoprovidereal-time,read-writeaccesstoprocessdata.OPCDA3.0isthelatestversionofthisstandard,whichprovidesbettersecurityandperformancethanpreviousversions.ImplementingOPCDA3.0clientinDelphiisataskthatrequiresunderstandingofOPCarchitecture,Delphiprogramminglanguage,andOPClibraries.
OPCDA3.0Architecture
OPCDA3.0followsaclient-servermodel,wheretheOPCclientcommunicateswiththeOPCservertogetdatausingtheCOM/DCOMtechnology.COMisacomponenttechnologyforbuildingsoftwarecomponentsindifferentprogramminglanguages.DCOM(DistributedCOM)isanextensionofCOMthatallowscomponentstocommunicateoveranetwork.OPCDA3.0usesDCOMforremotecommunicationbetweentheclientandserver.
AnOPCserverprovidesdatafromadatasourcetotheOPCclient,whichcanbeanothersoftwareapplicationorahardwaredevice.Theserverinitiatescommunicationwiththeclientbyprovidingalistofavailabledataitems.Theclientselectssomeoftheseitemsandsubscribestothemforupdates.Theserversendsupdatestotheclientwheneverthedatachanges.
TheDelphiProgrammingLanguage
Delphiisahigh-level,object-orientedprogramminglanguagebasedonthePascallanguage.ItiswidelyusedfordevelopingWindowsapplicationsandsupportsbothevent-drivenandmulti-threadedprogramming.Delphihasarichsetoflibraries,includingcomponentsforvisualprogramming,databaseaccess,networkcommunication,andmore.DelphialsosupportsCOM/DCOMtechnology,whichmakesitsuitablefordevelopingOPCclients.
ImplementingOPCDA3.0ClientinDelphi
ToimplementanOPCDA3.0clientinDelphi,weneedtofollowsomesteps:
1.InstallOPClibraries
WeneedtoinstallOPClibrariesthatprovidetheCOMinterfacesandfunctionsweneedtocommunicatewiththeOPCserver.ThereareseveralOPClibrariesavailable,includingOPCFoundation’sofficiallibraries,Softing’sOPCToolbox,orKasslGmbH’sOPCclienttoolkitforDelphi.Afterinstallingthelibrary,wecanaddthenecessarycomponentsandobjectstoourapplication.