13 Replies Latest reply on Nov 27, 2017 1:51 PM by gmichaud-verreault

    PI OPC Interface Excmax sends wrong value

    Olav

      Hi.

       

      I have an OPC interface where a specific tag has Excmax set to 300 sec and Compmax set to 700 sec. It is a digital tag, which has the values 0 or 1. However, every time Excmax triggers, it will send 0, even if the previous value sent by the interface was a 1. Any ideas what could be causing this? I cannot find any problems anywhere.

        • Re: PI OPC Interface Excmax sends wrong value
          gmichaud-verreault

          Hi Olav,

           

          What is the polling method for your tag (advise or polled) and what version of the OPC DA interface are you using?

          Could you also share your compression/Exc settings? I would also take a look at the value using any OPC Client, to see what the value really is.

           

          Gabriel

            • Re: PI OPC Interface Excmax sends wrong value
              Olav

              Hi.

               

              The polling method for this tag is advise tag. The compression settings are shown below in the screenshot.

               

               

              I don't have access to the interface node today, so I cannot check the version yet. It is placed on a restricted network. I am planning to have a look at it tomorrow. I will also check the value with an OPC Client to see. The reason we discovered this is because we have another instance of the interface reading the same tag and writing to a different PI data archive, and sometimes the values were different. That is, whenever there is a real change from 0 to 1, or from 1 to 0, the timestamps are the same in both data archives. But it seems that if excMax kicks in (Or it could maybe be compression causing it) a 0 will be stored in the PI Data archive, and then another 0 will be stored when the real value goes from 1 to 0.

               

              I never see a 1 being stored by exception or compression, ever. Only zeros. This is true for both instances, in both PI data archives.

               

              Edit: Below you can see a screenshot from PI Datalink. There is one instance where one of the Data archives get a wrong value, and another where it is correct on both tags.

               

            • Re: PI OPC Interface Excmax sends wrong value
              Olav

              I have now checked the message log on the interface node. It seems that the timestamps are coming from the OPC Server, which is on the same node as the interface. However, there is about close to a two minute delay between the timestamp and the time that the value comes in to the interface and is being sent to the PI Server. This means that the new value is being sent after ExcMax value has been sent, but with an earlier timestamp.

               

              So, any suggestions on how to solve this? Does the timestamp come from the device that the OPC Server is reading from? Is the only solution to drop ExcMAx, or to make sure all nodes are time synchronized?

                • Re: PI OPC Interface Excmax sends wrong value
                  gmichaud-verreault

                  This will also depend on your scan frequency (scan class) since this is a polled tag. If you want to get the event as soon as it changes between "0" and "1", then I would suggest setting the tag as advised. You will want to make sure to run the latest version though since older ones has issues with ExcMax and advise tags.

                   

                  Concerning the timestamp, you can configure the timestamp source at the interface instance level with the /TS parameter.  In ICU:

                  --

                  Gabriel

                • Re: PI OPC Interface Excmax sends wrong value
                  Olav

                  It should be an advise tag. It is set with location 3 = 1. And scan class 1, which is set to 53 ms as far as I can tell. The OPCInt version is 2.5.0.9. UniInt version is 4.5.5.22.

                  • Re: PI OPC Interface Excmax sends wrong value
                    Olav

                    Thanks for all your help. It might take a few weeks to get the upgrade done, due to operational limitations. I will report back with the results.

                    • Re: PI OPC Interface Excmax sends wrong value
                      Olav

                      I have a follow-up question. I have proposed to upgrade the OPC Interface, but I've been told there is a problem with that, because the interface node is running PI APS, and I understand the interface version we have is the last version to support PI APS.