OPC Connection Tag Limit?

Little late to the conversation but I am having a problem related to this. I am using a struct for positions on a conveyor. I am using indraworks/bosch PLC. Randomly one day, some of these tags were broken with “error configuration”. My fix was to create another OPC connection with the same end point, I counted it out, each new connection could only handle 76 of my position tags. I am happy to share a screen shot of my UDT for this tag if necessary to understand my issue further. My fix works for now but I can’t believe that 76 tags would tap out an OPC connection and the fix is to create another connection with different name but same endpoint…

There’s no client side limit on the number of tags in an OPC connection.

Combined with the info from your other post I saw just now it seems pretty clear the server has some limit to the number of MonitoredItems per Subscription or something like that. Your “excess” tags go to Error_Configuration in Ignition, which is likely due to a failure to create the MonitoredItems for some reason.

The loggers found searching “OpcUaSubscriptionModel” and “OpcUaSubscriptionSynchronizer” and setting them to TRACE can confirm this. When the items fail to get created the StatusCode returned by the server will be logged.


That helps me understand what happened, thank you! How would you approach fixing this problem? I don’t want to go down the wrong path here.

Start by confirming this is the issue with loggers.

If it is, I’d then call to the vendor to see if it’s configurable.

If it’s not configurable, you should at least be able to use separate Tag Groups instead of separate connections.

Worst case, you can use a single Tag Group just for this server but put it into OPC Read Mode instead of Subscribe Mode.

The annoying this is that I had a screenshot of the issue you are explaining, I just did not understand it fully until now.

I will reach out to the vendor, thanks for the help!

Would OPC read mode work in my situation? There are parts of this struct I do need to be able to write to. For instance, I have a template that allows me to shift data to a new position. I.e. - I can move my information for position 1 to position if needed.

I am hoping it is configurable to save the hassle in the future, but for now it works, so I appreciate the help once again!

Read vs Subscribe mode is just about how data is acquired, you can still write to those tags in either mode. Subscriptions just generally offer better performance for both sides.