7 Replies Latest reply on Oct 9, 2018 12:36 PM by ChipStacy

    Intermittent issue with RSLinx - OPC Interface and no data


      We have well over 100 Rockwell PLC's of varying models SLC500, Control Logix, Compact Logix etc. Often our portable systems are powered down and disconnected from our PLC network. When reconnected we often experience issues with no PI data showing up on Processbook. We get the dreaded 'Trace'. The PLC's have no issue when connecting to our PLC network and are easily seen via programming software and RSLinx.


      There are several scenarios that occur with regards to getting data back into PI. As a starting reference we have two PI servers, a primary and backup. Both servers run RSLinx and PI's OPC interface version and UniInt (universal interface)

      First scenario with no PI data:

           PLC is connected to network but cannot connect to or see any data with PI OPC Client. Solution is to shutdown opc interface. Open RSLinx, delete the topic for the affected plc, rebuild the topic, restart the interface and then we're back in business.


      Second scenario is that we can see PLC data in OPC client on both servers but still get 'Trace' with Processbook. In this case, we restart the opc interface on the backup server, wait for it to be started, then stop the interface on the primary server, which in turn forces the backup to become the primary, then restart the old primary (now the backup server) and then Processbook data starts showing data points from the PLC.


      This is a regular issue with anything that's been disconnected from the network for any length of time. Sometimes it comes back and many times it doesn't.

      We use the same OPC interface for another portable system by GE that doesn't use a PLC but rather a PC and we've never had an issue. ONLY with Rockwell PLC's.


      We've yet to determine what is causing this. We believe this to be an RSLinx issue but have had no luck with Rockwell as of yet in resolving the issue.


      Thanks for your comments in advance.



        • Re: Intermittent issue with RSLinx - OPC Interface and no data

          Hi Chip,

          Not sure if I understand your architecture correctly but is the RSLinx OPC Server on a machine that picks up the PLC data on the network?  Have Rockwell suggested to upgrade to FactoryTalk Gateway?


          Have you considered setting up another instance of the PI OPC Interface that connects to an OPC Server dedicated to these 'portable' PLC's?  I must admit I wouldn't be relying on an OPC Server to reliably pickup data sources that are added to the network without requiring a restart.  Some OPC Servers have config that enable periodic checking of the network but certainly not all.

            • Re: Intermittent issue with RSLinx - OPC Interface and no data

              Thanks Karl. These are redundant servers. Both servers have network interface cards that connect directly to our PLC network to access the PLC tags.



              The fixed and portable PLC's all connect to the same network. It's just the portable ones that, when disconnected from the network for a period of time and then are reconnected, communicate fine on the PLC network but fail to reestablish connection to the PI servers, although per my original post, occasionally show data on the OPC client but not in Processbook.


              Rockwell has not suggested FactoryTalk as of yet. We have not yet setup another instance of the OPC interface yet.

                • Re: Intermittent issue with RSLinx - OPC Interface and no data

                  So you are using two different OPC Servers, RSLinx for Rockwell and another for GE.  I'm fairly confident your issue is not the PI OPC Interface.  Once the client connection has been made to the OPC Server, it adds the tags and builds the groups for what is available at the time.  This is why you can use another OPC Client and see the data later as it makes a new call to the OPC Server and discovers the new items.  One way you could possibly make the PI OPC Interface make it refresh the connection and discover the items is to Scan Off the applicable PI Points once you have disconnected the portable PLC then scan them back after the portable PLC has been reconnected to the network.


                  Alternatively as I suggested earlier, you could make another instance of the PI OPC Interface specifically for the portable PLC's and restart the interface when required so you don't interrupt the data flow from the fixed PLC's.  Give that instance a unique Point Source name which will reduce startup times.