Client Tags Not Reading

Well i have came across a wierd one today. We are running 7.5 with 2 projects running. We are having issues with the clients not reading OPC data when they are started up. You can let it set for several minutes and sometimes it will start reading values. The thing is a designer running on the same machine has no issues with reading OPC tag values during this same time. We are seeing this behavior with both projects and on every client dosent matter which machine. We reset the gatway yesterday evening and all was working like we would expect but came in this morning and we were back to having the client read errors.

Note that the overlay on the components are a green ? if that gives you anymore info.
Any Ideas??

Are there any useful errors in the System Console logs in the gateway? Also, does you OPC server show as “connected” on the Status -> OPC Connections page in the gateway?

I would recommend upgrading to the 7.5.1 beta. I’m fairly certain that what you’re seeing is a problem with the quality overlay system that has been fixed.


Ok we will try that and see how it goes. Not sure this will be the entire issue because we are seeing some other weird behavior out of the system. All of a sudden this morning all expression tags stoped reading value from OPC. The all threw null exception errors even though the tags they were looking at had a valid value and showed good quality. Once again after resetting server this has gone away for now. Will let you know how upgrade to the beta goes though.

Well upgraded to the Beta and still doing the same thing. I have looked at the logs and don’t see any indications of any issues.

Here is a bit more detail on what is happening.
When gateway is first started and client is opened the tags in the client take around 10 or so seconds to load when opening screen.
This morning after gateway has been running 14 hours opening a client the same screen takes over 1.5 minutes to load the tags.
In both instances this time delay happens each time a screen is loaded with tags from a different OPC-UA device for the first time. After that the tags update as expected.

I could see some delay on loading the tags for the first time on a client depending on how they are cashed to the client but what i don’t understand is the longer the gateway runs the longer it takes for the tag to initialize on the clients.

Let me know what log files to look at and i will be glad to look at and send along. Also i am not resetting the gateway till we can resolve this issue. Also note i have tried running only single project and also tried running on a different physical server with same results.

We got a chance to look at this project and found the solution. It will be in 7.5.1.

The root problem was the combination of expressions that reference other tags along with leased scan classes with a non-0 slow rate were causing the tags to cycle between leased and not leased. A temporary workaround for anyone seeing this issue is to change over to a direct scan class until you can upgrade to 7.5.1.