How to connnect Third party remote OPC server into 800xA system
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As stated by Ingo, for stability reasons a dedicated OPC tunneler is preferred over using DCOM.
But 800xA can do DCOM out of the box; just specify a different node name on the Service Provider definition.
Just remember a few more prerequisites need to be fulfilled to be able to use DCOM.
The Configuration User's Guide states (some) of them.
In 800xA Version 5.0 I had used remote OPC Connection. It had worked well but after lost connection the reconnect was not automaticly done. I had to stop/start the service. Now I use a tunneler and it works fine.
Maybe this problem don't exist in newer versions but I would also recommend a tunneler software.
In addition to the above answers which are perfect solution to connect.
I would like to add few more suggestion.
ABB has "Interface handler" product to connect to the third party OPC servers and Specially designed "REUSE OC library" can be found to have all types of Data like AI, DI, DO,TEXT, AI64 , VALVE etc etc.