In this article, I will show how to use OPC Data event to control something. For example, doing some operation if value of specified OPC Tag changed.
In COPCDLL, it is “datChange” event can be used to detect if specified OPC tags data changed or not.
The VS C# example below shows if data of OPC tag which has index number 1 is changed, the code will write data value 111 to OPC tag has index number 2.
Private Sub copc1_datChange(tagIndex As Integer) Handles copc1.datChange
Try
Select Case tagIndex
Case 0
Case 1
copc1.opcWrt(2, 111)
Case 2
End Select
Catch ex As Exception
End Try
End Sub
In COPC32, it is event ‘datChngX’ can do the same operation.
The VB.net example below shows id (index numner) of OPC tag that it’s data is changed.
Private Sub Axcopc1_datChngX(sender As Object, e As AxCOPC32.__copc_datChngXEvent) Handles Axcopc1.datChngX
Label1.Text = e.id
End Sub
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