What is the best approach to implement an OPC interface to a PLC when both direct access to the PLC or its HMI is available?
The OPC DA interface communicates to an OPC Server. So you must have an OPC Server in between that ultimately communicates to the device.
May be i needed to be clearer. I can install for instance a kepware opc server on a Pi interface server and use the appropriate driver to connect straight to a PLC. Alternatively i can use the OPC server provided by the PLC HMI maker and set the interface that way. My question is meant to determine the pro and con of using one approach versus the other if both options are available.
I have done OPC DA interfaces to PLCs both ways that you mention. The advantage I see with Kepware is that if you go with the Manufacturing Suite, you can use the same OPC server to collect data from different PLC makes and models. I have several instances where I collect data from different brands of PLCs via 1 PI OPC DA interface and KepServerEx.
Retrieving data ...