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OPC - The RPC connection is disconnected

Dear All, i am trying to connect a 3rd party software to DeltaV opc server,  while the data gets collected in OPC client as requested for some time, the DeltaV OPC server seems to froze and throws an error  in the client " RPC Connection is disconnected".  

My questions are : Can DeltaV OPC server handle Asynchronous and Synchonous reads.  If so why is the OPC server hanging up after a period of time.  The problem seems to go away once i restart the OPC client application,  this informs me that either the groups created in the OPC server are not handled or killed and only get accumulated( garbage management)  . My understanding and research suggests that the OPC group objects accumulation is overcranking the DeltaV OPC licensed tag count,  as  such the OPC server freezes and can only come back alive after a restart. The restart i suspect is killing all the existing groups, hence there would be no issues until the groups get accumulated.  

Somebody please enlighten about this issue.

Thank you

Another Humble DeltaV User


4 Replies

  • Hi Venu,

    My understanding of the OPC server is that it just makes the DCS tags available for the OPC client to retrieve data; there are no groups created on the OPC server itself, only on the OPC client. The client then requests data at the frequency dictated by the config that it uses at startup.

    I had a similar issue with RPC connection calls, and I think it was traced to rogue network traffic causing various switches to start blocking ports (some sort of fancy IT things which I don't really understand). I'd check that kind of thing first. After that its the same old things like firewall settings (avoid going across firewalls as much as possible), NAT tables (I don't think OPC likes NAT tables), connection identities, etc., etc.

    Sorry I can't be of more help. What 3rd Party software are you trying to connect with? I have an OSIsoft PI-OPC interface and it works fine. We've also used Matrikon and Kepware and they all work fine.
  • Hi Venu,
    I also had a similar problem before when I was using OPC Mirror between DeltaV and PCS7 OPC Server. The problem was that DeltaV OPC Server was trying to write in one PCS7 OPC parameter not existent (we got a wrong OPC parameter list from costumer). Only when we tried to write in that specific parameter, the RPC connection was lost. Reading was not a problem, only writing. As long we were not writing all the time, it was very hard to find the reason.
    Maybe you should take a look if the mapping is correct.
  • To answer your questions, yes the OPC server can support sync and async read and write. Do you see any errors in the DeltaV OPC server machine application or system logs to indicate that the server is freezing (can you connect a new client once the existing client bombs out?) You are getting an error at the client, so it is perhaps worth testing that client against a different opc server for confirmation. Regarding licensing, if your client is in fact adding and deleting items from groups dynamically, I believe the license count will indeed increase over time. You can verify this using deltav diagnostics for the OPC server.
  • In reply to Youssef.El-Bahtimy:

    For the latter point, yes, dynamic creation of groups will consume additional OPC DA licenses. You will eventually reach the license limit, where the server indicates no additional licenses are available for adding more groups / tags. The DeltaV OPC DA server has a 7 minute dissolution timer, so stale / unused groups will not persist indefinitely.