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  1. Forum
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  5. QuickOPC-Classic in .NET
  7. Reading, Writing, Subscriptions, Property Access
  9. Older Tag Values Being Provided - Automatic Subscription Question

Older Tag Values Being Provided - Automatic Subscription Question

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28 Feb 2022 17:13 #10665 by support
Replied by support on topic Older Tag Values Being Provided - Automatic Subscription Question
Hello.

Do I understand it correctly that
- the customer is reading the items periodically from time to time, but is not subscribed to the same items at the same time.
- the customer is now using DADataSource.Device
- software version is 2021.3
- the item caching is disabled.

If the above is true, I actually believe it is much more likely the it is the OPC server that is delivering the stale values (even though it does not happen with Quick Client)

Can the customer deploy the OPC Analyzer and capture the communication - together with logs from his client app showing what were the values received?

Thank you

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28 Feb 2022 14:15 #10659 by ZParham
Replied by ZParham on topic Older Tag Values Being Provided - Automatic Subscription Question
Thank you very much!

We tested with an OPC-DA client not created with the OPC Data Client toolkit (Quick Client) and did not see the same behavior, which is what leads us to believe this is client-side.

I had the end user test with the examples at opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...ReadParameters~DataSource.html and he saw the same behavior.

Even after disabling the cache, he has continued to see stale values every so often. He also changed the DAReadParameters to DADataSource.Device to see if that might help, and he has been getting fewer stale values, but they have not completely gone away.

Do you have any insight as to what might be occurring?

Thank you again, as always!

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24 Feb 2022 14:35 #10652 by support
Replied by support on topic Older Tag Values Being Provided - Automatic Subscription Question
Hello.

Yes, in 2020.3 the default is that automatic subscriptions are turned off (kb.opclabs.com/What%27s_new_in_QuickOPC_2020.3#OPC_Classic_2 ); and, their parameters, if needed, are configured differently from what the "pinned" post suggested. I have unpinned it.

With 2021.3, if this is happening, I would most likely guess that this is a problem on the server side. It could/should be possible to use OPC Analyzer to figure it out.
Also, try reading directly from the device (I am not saying that is the right practice, but it would at least bring some more info; and if it does not harm performance, it can even ne the solution).

If, theoretically, there was a bug in QuickOPC item caching (because the caching seems to be related to the issue), it would go away when the caching is turned off - this is described here: opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...html#OPC%20DA%20Optimizer.html .

Best regards

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24 Feb 2022 14:22 #10651 by ZParham
Older Tag Values Being Provided - Automatic Subscription Question was created by ZParham
Hello!

I have a customer running 2021.3 who is running into an issue where despite using ByValueAge and having ValueAge set to 10, the server sometimes provides 2+ hour old values. We initially looked into turning subscriptions off as explained in the following pinned post: www.opclabs.com/forum/reading-writing-subscriptions-property...scriptions-made-with-opc-reads - However, the parameters do not seem to exist.

After doing some digging, the customer found the following statement in another post:

"In fact, we will be turning off the automatic subscriptions (by default) in the upcoming QuickOPC 2020.3, because except in cases like the one described above, it brings more problems than it resolves.” www.opclabs.com/forum/reading-writing-subscriptions-property...riptions-or-subscribe-manually

Did this ever happen? If so, do you have any other insight as to why we might be receiving older values for reads?

Thank you in advance!
Zachary Parham

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  5. QuickOPC-Classic in .NET
  7. Reading, Writing, Subscriptions, Property Access
  9. Older Tag Values Being Provided - Automatic Subscription Question
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