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1、Using Visual Basic As An OPC Client,John WeberPresident&FounderSoftware Toolbox,Iwebsite:http:/,Your OPC Server,Copyright Software Toolbox,1999,2000,2001 All Rights Reserved Worldwide.Software Toolbox is a registered trademark of Software Toolbox,Inc.,Presentation Updated 3/2001,Agenda,OPC-Review of
2、 the BasicsOPC-TerminologyOPC&VB 101-Automation Wrapper&Object ModelBuilding Your VB Client-Read data-7 easy steps with code from start to finishHousekeepingHandles Handles Everywhere-how the server and client correlate the data each is managing in your programWriting DataFuture ideas to considerNew
3、 developments since original presentation in 10/99Resources for future learning,OPC-Review of the Basics,OPC is based on the Microsoft Component Object Model(COM)OPC stands for OLE for Process ControlOPC is managed by the independent OPC Foundation(www.opcfoundation.org)There are over 200 member com
4、panies supporting the OPC specificationOPC defines a standard method for connecting automation application software,OPC and VB 101-Terminology,OPC Server-a piece of software supporting the OPC specification-an OPC Data Access Server is a driver that handles connectivity to PLCs or other automation h
5、ardwareOPC Item-A single tag or data point managed by the OPC server-i.e.one data point in a PLCOPC Group-a user defined grouping of OPC items.Created by the OPC client as a way of organizing data items around logical process areas or equipment.Collection-a grouping of objects of the same data type-
6、for example,each OPC server has an OPC items collection containing one software object for each OPC item.,OPC and VB 101,Visual Basic supports COMCOM implementations from Visual Basic use what is called an“Automation”interfaceThe OPC Foundation supplies the source code to an“Automation Wrapper”DLL-m
7、ost OPC vendors provide a compiled versionAutomation Wrapper connects VB to OPC,OPC and VB 101,Automation Wrapper DLL lets VB access OPC Servers and their underlying Groups and Items,Object model for the Automation Wrapper-the wrapper lets the VB user connect to an OPC server using standard Object.p
8、roperty and Object.method syntaxes,OPC and VB 101,Your VB Program with the Automation Wrapper object included in it,Your OPC Server and its object model,COM/DCOM,The Automation Wrapper connects to the OPC server and creates the groups and items in the server and givesyou references to them in yourVB
9、 program in an Objectmodel that mirrors that of theserver,OPC&VB-Making The Connections,Connect to the OPC Server,Add Group(s),Add Item(s)to Group(s),Activate Groups&Items,Data Change Events Fire,De-Activate Groups&Items,Remove Item(s)from Group(s),Remove Group(s),Disconnect from the OPC Server,User
10、 Program Handles Data-Log,Display,Graph,etc,Optional-your program can add/remove items and groups and activate/deactive items at runtime based on user defined conditions,Tools Youll Need To Build Your Application,If you want to build an OPC client in VB and test it,youll need the following tools:Vis
11、ual Basic 5 or 6 running on Windows 95,98,or NT any VB edition will do the jobAn OPC ServerThe OPC Automation WrapperYou can get the last two items including a sample test OPC server at(see last slide for exact link).There is no charge for the Automation Wrapper and sample OPC demonstration servers
12、are free also.,Building Your VB Client-Step 1,Install the OPC Automation Wrapper DLL on your PCStart a new VB projectIn VB,click on Project-References on the VB menu barThe OPC Automation Wrapper appears on the dialog as“OPC Automation 2.0”-select it as shown here.,Building Your VB Client-Step 2,Fir
13、st you need to declare some variables in the VB code window in the General Declarations area as shown here,Option ExplicitOption Base 1 Makes all arrays start with an index of 1Dim WithEvents AnOPCServer As OPCServerDim WithEvents ConnectedOPCServer As OPCServerDim ConnectedServerGroup As OPCGroupsD
14、im WithEvents ConnectedGroup As OPCGroupDim OPCItemCollection As OPCItemsDim ItemCount As LongDim OPCItemIDs(10)As StringDim ItemServerHandles()As LongDim ItemServerErrors()As LongDim ClientHandles(10)As Long,These lines create objects you will use to manage your OPC server connection and a group-yo
15、u could add more than one group if you wanted to,These lines create objects you will use to manage your OPC Items-we are setting up our sample to read 10 items-you setup as many as you need,Building Your VB Client-Step 3,If you want your VB project to connect to your server at startup,use the name o
16、f your server(ask your server vendor)and enter the following code in the Form Load subroutine for your project-our server name is“KepServer”,Dim ConnectedServerName As StringCreate a new OPC Server objectSet ConnectedOPCServer=New OPCServerLoad the selected server name to start the interfaceConnecte
17、dServerName=“Developer-Enter Your OPC Server Name Here in quotes”Attempt to connect with the server(Local only in this example)ConnectedOPCServer.Connect(ConnectedServerName),Building Your VB Client-Step 4,Next,youll go ahead and add a group right after you get your connection to the OPC server.Ente
18、r this code right after your code for connecting to the server in the Form Load subroutine of your project,Prepare to add a group to the current OPC Server Get the group interface from the server objectSet ConnectedServerGroup=ConnectedOPCServer.OPCGroups Set the desire active state for the groupCon
19、nectedServerGroup.DefaultGroupIsActive=TrueSet the desired percent deadband-enter an integer from 0 to 100 for the deadbandConnectedServerGroup.DefaultGroupDeadband=0 Add the group and set its update rate-enter whatever group name you want in place of“DataGroup1”Set ConnectedGroup=ConnectedServerGro
20、up.Add(“DataGroup1”)Set the update rate for the group-enter an long integer value representing the millisecond group update rateConnectedGroup.UpdateRate=500 The following line is crucial-without it you wont be subscribed to the server and DataChange events will not fire!ConnectedGroup.IsSubscribed=
21、True,Building Your VB Client-Step 5,Next youll go ahead and add some items.This code follows right after the group add code in the Form Load subroutineFor the item names,enter valid item names for your OPC server.Refer to your OPC servers documentation for valid item naming conventions.We are going
22、to be reading some data from a GE PLC here so we will use their memory conventions.The OPC server we are using uses the syntax“itemnameupdaterate”,ItemCount=4Dim i As IntegerFor i=0 To 3 This line builds a string like“GE9030.R110”-a valid item name for the OPC server we are using OPCItemIDs(i+1)=“GE
23、9030.R”&(I+1)&“10”ClientHandles(i+1)=I Sets a reference pointer number for this point OPCItemActiveState(i).Value=1 Tells the server we want this item to be activeNext ISet OPCItemCollection=ConnectedGroup.OPCItems Gets an items collection from the current GroupOPCItemCollection.DefaultIsActive=True
24、Sets the items collection to activeThis line adds the items weve chosen to the items collection and in turn to the group in the OPC ServerOPCItemCollection.AddItems ItemCount,OPCItemIDs,ClientHandles,ItemServerHandles,ItemServerErrors,Building Your VB Client-Step 6,Now,assuming you have all valid it
25、em names and your OPC server is ready to go,all you need to do is add code to react to the DataChange events that your OPC server will fire back to the Automation DLL,which in turn will fire an event in VB for youIn your program,you created an object variable called“ConnectedGroup”in step 2-this obj
26、ect will fire an event called“DataChange”for anytime one of the items in your group has new data for youThe DataChange event tells you how many items changed,gives you back the client handles so you know which ones changed,and the data,quality,and timestamp information,Building Your VB Client-Step 6
27、,Go ahead and build the objects on your form to display your data.For our form,we built one with 3 arrays of text boxes-one each for the data,quality,and timestamp information.We named them txtData,txtQuality,txtTimeStamp respectively.,Building Your VB Client-Step 6,Dim i As Integer For i=1 To NumIt
28、ems txtData(ClientHandles(i).Text=ItemValues(i)If Qualities(i)And&HC0 Then txtQuality(ClientHandles(i).Text=Quality Good Else txtQuality(ClientHandles(i).Text=Quality Bad End If txtTimeStamp(ClientHandles(i).Text=TimeStamps(i)Next i,Now in the VB Code window,use the combo boxes at the top to go to t
29、he ConnectedGroup objects DataChange event subroutine-enter this code to update your text boxes.Note this code assumes you have named your text boxes as we have in our example and built an array of text boxes as we have in our form.If you named your text boxes differently,then you will need to adjus
30、t this code accordingly.The variables ItemValues,Qualities,ClientHandles,and TimeStamps are all variables passed to you by the Automation Wrapper DLL and your Connected Group object when the DataChange event fires,The Qualities data array can contain a variety of very hardware specific data about wh
31、y communications failed-a value of Hex C0 is returned when everything is OK,Timestamps are returned in GMT or Universal Time,Building Your VB Client-Step 7,Now if you have not done so,save your project and form in VBRun your project.If you have specified a valid OPC server and Item names and your OP
32、C server is running and ready,then when you run your project,it should immediately start updating the text boxes on your form,If things arent working.,If you do not have communications,check the followingDo you have the OPC server name specified correctly in the form load routine?Check with your OPC
33、 server vendor for the right name to useAre you using valid item naming syntaxes for your pariticular OPC server?Do you have the cabling and hardware setup right between your OPC server and your hardware?,Housekeeping,This program was a very basic one-in reality you need to add at least one more sec
34、tion of code in order to make sure you clean up your connections to the OPC server before you exit your program.Otherwise the OPC server will still think you are connected and hold open memory to service you that it could otherwise release.Enter the code on the following slide in the Click()event on
35、 the“Disconnect and Exit”command button you put on your formThis code makes sure you remove the item,items collection,group,and groups collections from the server then disconnect from the server upon exit.,Good memory management dictates that you“undo”everything that you“do”,Housekeeping-Exit&Cleanu
36、p Code,=First Remove All of Our Items=ItemCount=1 Provide an array to contain the ItemServerHandles of the item we intend to remove Dim RemoveItemServerHandles(10)As Long Dim RemoveItemServerErrors()As Long Get the Servers handle for the desired items.The server handles were returned in add item sub
37、routine.In this case we need to get only the handles for item that are valid.Dim i As Integer For i=1 To 3 We have 3 data points we are reading In this example if the ItemServerHandle is non zero it is valid If ItemServerHandles(i)0 Then RemoveItemServerHandles(ItemCount)=ItemServerHandles(i)ItemCou
38、nt=ItemCount+1 End If Next i Item count is 1 greater than it needs to be at this point ItemCount=ItemCount-1 Invoke the Remove Item operation.Remember this call will wait until completion OPCItemCollection.Remove ItemCount,RemoveItemServerHandles,RemoveItemServerErrors Clear the ItemServerHandles an
39、d turn off the controls for interacting with the OPC items on the form.For i=0 To 2 ItemServerHandles(i+1)=0 Mark the handle as empty Next i Set OPCItemCollection=Nothing,=Now remove the group=Remove the group from the server ConnectedServerGroup.Remove(Groupname)Release the group interface and allo
40、w the server to cleanup the resources used Set ConnectedServerGroup=Nothing Set ConnectedGroup=Nothing=Now Disconnect from the OPC Server=ConnectedOPCServer.Disconnect Release the old instance of the OPC Server object and allow the resources to be freed Set ConnectedOPCServer=Nothing=Now exit the pr
41、ogram=End,Handles Handles Everywhere,In the preceding program,you probably saw that we used the ClientHandles and ItemServerHandles variables a lot.Just what are these“handles”A handle is an identifier assigned in software to point to a memory location or data point.When you connect to an OPC Server
42、 and create items,the OPC Server assigns a handle for each item-a large number.Likewise,when your OPC client connects to the server,it needs to have a handle to uniquely identify each item.Handles as numbers are much easier for code to deal with quickly and efficiently behind the scenes than long na
43、mes.Refer to Step 5-when you added items,you set your handles for the client side in the array variable ClientHandles()When you invoked the.AddItems method,you passed the server your list of ClientHandles()-the OPC server returns a list of the corresponding handles it assigns in the array variable I
44、temServerHandles()You use the ItemServerHandles()to tell the server which item you are interested in for future synchronous read and write operations on a single item.,Handles Handles Everywhere,The following picture should help you understand what handles look like inside the program.The numbers us
45、ed here are actual numbers that were assigned in running the program created by this tutorial.Your ItemServerHandles will be different as each server on each PC assigns handles differently to assure uniqueness.,Array Index,ClientHandles(),ItemServerHandles(),1,2,3,4,0,1,2,3,38145856,38145968,3814608
46、0,38146192,Assigned by the OPC Server and passed back to your program by the Automation Wrapper DLL when the AddItems method completes and returns,Assigned by your program and passed to the OPC Server when you call the.AddItems method.Should be numbers that are useful to you in your code in working
47、with and manipulating the data,Writing a Value-Step 1,Of course now that you are reading data,you want to write some data.Add a text boxes and an array of command buttons to your form as shown below.Name your text boxe txtValueToWrite and the command button array cmdWriteValue.For simplicity,we will
48、 stick to just writing items that you already subscribed to when we loaded the form.,Writing a Value-Step 2,When you click on the write command buttons,the event handler in VB hands you an index from 0 to 3 which matches up to the items that we added when the form loaded.The following code performs
49、an OPC Synchronous Write to the chosen item-place this code in the cmdWriteClick event in your VB program,Write only 1 item this time ItemCount=1 Create some local scope variables to hold the value to be sent.These arrays could just as easily contain all of the item we have added.Dim SyncItemValues(
50、1)As Variant Dim SyncItemServerHandles(1)As Long Dim SyncItemServerErrors()As Long Get the Servers handle for the desired item.The server handles were returned when we loaded the form.We use the index of the command button clicked to tell us which item to change SyncItemServerHandles(1)=ItemServerHa
