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Step 2: Basic construction of VB.NET

We will explain the basic construction details on the VB.NET side.

Please note that the following is only an overview, so please check the sample for details.

 

 

 

 

Library References

 

To connect to the OPC server, you need to use "OPCDAAuto.dll", so you need to set a reference to the library.

 

1.Select "Project" - "Add Reference"

 

 

2.Select "OPC DA Automation Wrapper" from "COM"

 

 

If it is not in the list, click "Reference" and reference the following DLL directly.

 

C:\Program Files (x86)\Common Files\Roboticsware\Ver6\opc\OPCDAAuto.dll
 

 

 

3.Select "View" - "Object Browser"
 

 

4.Verify that the OPCAutomation library is referenced and the list of published interfaces is displayed.

 

 

 

Creating a OPC object

 

To access an OPC server from Visual or Basic, use the OPC Automation interface.

 

There are four main interfaces:

•Server Interface

•Group Collection Interface

•Item Collection Interface

•Browser interface

 

This section describes how to get and create server, group, and item objects.

Specifically, we will establish a connection with the OPC server, create a group, and add items.

 

 

1.Preparing properties for automation

 

Declares various constants and properties that store the OPC automation object. The property type specifies the OPC automation class.

 

 

 

2.Connecting to the OPC Server

 

Create an instance of the "OPCAutomation.OPCServer" class and issue the Connect method to the created object.

Private Function FnConnect(ByVal vProgId As String, Optional ByVal vNode As Object = Nothing)
    Try
        mvServer = New OPCAutomation.OPCServer
        mvServer.Connect(vProgId, vNode)

 

3.Adding a group

 

Issue the Add method to the OPC group object to add a group. Specify the properties accordingly.

Here, we will use the asynchronous method later, so set the lsSubscribed property to True.

Private Function FnAddGroup()
    Try
        'AddGroup
        mvGroups = mvServer.OPCGroups
        mvGroup = mvGroups.Add(mvGroupName)

        'Property Set
        mvGroup.IsActive = False
        mvGroup.IsSubscribed = True
        mvGroup.UpdateRate = CInt(txtUpdateRate.Text)

 

4.Add items

 

Issue the Add method to the OPC item object to add the item.

Here we will register fixed items (U01.F01.T01 to U01.F01.T04), but in reality, items will be registered based on user specifications or configuration files.

Private Function FnAddItem()
    Try
        'AddItem
        mvItems = mvGroup.OPCItems
        Dim Errors As Array = Nothing
        mvItems.AddItems(mcItemCount, mvItemName, mvCHandles, mvSHandles, Errors)

 

5.Disconnecting from the OPC server

 

The connection must be closed when the OPC application is closed.

The OPC server does not know when the OPC application has ended, so it will always perform a disconnection process.

Private Function FnDisconnect()
    Try
        ' Delete items and groups,Server disconnect
        If mvItems IsNot Nothing And mvSHandles IsNot Nothing Then
            Dim vErrors As Array = Nothing
            mvItems.Remove(mcItemCount, mvSHandles, vErrors)
        End If
        If mvGroups IsNot Nothing Then
            mvGroups.Remove(mvGroupName)
        End If
        If mvServer IsNot Nothing Then
            mvServer.Disconnect()
        End If

        'Property Initialize
        mvSHandles = Nothing
        mvItems = Nothing
        mvGroup = Nothing
        mvGroups = Nothing
        mvServer = Nothing
        GC.Collect()