OPC Server示例教程：OPC客户端——VB.NET示例

OPC Server是一套利用微软的COM/DCOM技术实现工业自动化资料获取的架构。OPC Server提供OPC接口，它将与之相连的物理设备（PLC）的信息值通过接口返回到客户端应用程序。也就是说，客户端通过这些接口，可以获得与OPC Server连接的物理设备的信息。对于集成应用程序，只要支持OPC接口，就能轻易访问物理设备，而无需相关的技术信息。 程序设计者可以使用相同的程序代码，操作不同的硬件装置，充分达成软件复用的目的。

【OPC Server 最新版下载】

它使用OPC Server引入了简单的示例程序。此示例的代码使用OPC 如果从.NET访问OPC Server，则需要交换COM和.NET的包装器。 自动化包装器（OPCDAAUTO.DLL），因此它几乎等于VB6.0。

Declaration

Option Explicit

Public OpcServer As IOPCServerDisp
Public OpcItemMgt As IOPCItemMgtDisp
Public OpcItem As IOPCItemDisp

Private Const ItemMax = 8
Private Const OPC_DS_CACHE = 1
Private Const OPC_DS_DEVICE = 2

Dim ClientHandles(ItemMax) As Long
Dim ServerHandles As Variant
Dim bConnect As Boolean

连接到OPC服务器，创建OPCGroup和添加标签

Private Sub CONNECT_Click()
  On Error GoTo err_hd
  Dim i%
  If bConnect Then
    CONNECT.Caption = "Connect"
    Set OpcServer = Nothing
    Set OpcItemMgt = Nothing
    Set OpcItem = Nothing
    bConnect = False
    READ_Button.Enabled = False
    WRITE_Button.Enabled = False
    For i% = ItemName.lbound To ItemName.ubound
      ItemName(i%).Enabled = True
    Next i%
    Exit Sub
  End If

  '*** Connect to OPC Server ***
  Set OpcServer = CreateObject(Form1.ServerName.Text)
  If TypeName(OpcServer) = TypeName(Nothing) Then Return

  '*** Add OPCGroup ***
  Dim UpdateRate As Long
  Dim ServerHdl As Long
  UpdateRate = UpdateRateSet.Text
  Set OpcItemMgt = OpcServer.AddGroup("Group One", True, UpdateRate, 22, 1, 0, ServerHdl, UpdateRate)
  If TypeName(OpcItemMgt) = TypeName(Nothing) Then Return

  '*** Add OPCItems ***
  Dim ItemIDs(ItemMax) As String
  Dim AccessPaths(ItemMax) As String
  Dim Active(ItemMax) As Boolean
  Dim Errors As Variant
  Dim ItemObjects As Variant
  Dim DataType(ItemMax) As Variant
  For i% = 0 To ItemMax - 1
    Active(i%) = True
    ClientHandles(i%) = 22 + i%
    AccessPaths(i%) = ""
    ItemIDs(i%) = Form1.ItemName(i%).Text
    DataType(i%) = 2
  Next i%
  OpcItemMgt.AddItems ItemMax, ItemIDs, Active,ClientHandles,
            ServerHandles, Errors, ItemObjects, AccessPaths, DataType
  Set OpcItem = ItemObjects(0)
  bConnect = True
  CONNECT.Caption = "DisConnect"
  READ_Button.Enabled = True
  WRITE_Button.Enabled = True
  For i% = ItemName.lbound To ItemName.ubound
    ItemName(i%).Enabled = False
  Next i%
  Exit Sub

err_hd:
  MsgBox "Error connecting"
  For i% = 0 To ItemMax - 1
    Form1.Value(i%) = "Error"
  Next i%
End Sub

缓存读取

Private Sub READ_Button_Click()
  Dim ReadValue As Variant
  Dim pQuality As Variant
  Dim pTimestamp As Variant
  Dim Errors As Variant
  Dim i%
  Dim io As IOPCSyncIODisp
  Set io = OpcItemMgt
  '*** Cache Read ***
  io.OPCRead OPC_DS_CACHE, ItemMax, ServerHandles, ReadValue, pQuality, pTimestamp, Errors
  For i% = 0 To ItemMax - 1
    Form1.Value(i%) = ReadValue(i%)
    pTimestamp(i%) = DateAdd("h", 9, pTimestamp(i%))
    Form1.Time(i%) = pTimestamp(i%)
    Form1.Quality(i%) = pQuality(i%)
  Next i%
End Sub

SyncWrite

Private Sub WRITE_Button_Click()
  Dim WriteValue(ItemMax) As Variant
  Dim io As IOPCSyncIODisp
  Dim Errors As Variant
  Dim i%
  Set io = OpcItemMgt
  For i% = 0 To ItemMax - 1
    WriteValue(i%) = Form1.Value(i%)
  Next i%
  '*** SyncWrite ***
  io.OPCWrite ItemMax, ServerHandles, WriteValue, Errors
End Sub