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Timestamp refresh time - server side

Stefano Di Monte

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10/26/2017

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10/26/2017 - 05:40

Hi,
i’ve a question about management of refresh time of item’s timestamp value, server side in OPC DA.
Is there a specification about it?

I wonder why i have two differente implementations of OPC DA server that refresh the value of group’s timestamp in two different way:
– the first one refresh the value of timestamp every time it reads group’s values.
– the second one refresh the value of timestamp only when there is at least one value that changes.

Is anyone wrong?

Thanks

Guest

Guests

10/26/2017 - 22:43

I cannot comment on implementations, the OPC-F samples are quite old and haven’t been updated for more than a decade.

The timestamp handling is specified in the DA specification. See 4.2.6 “CACHE data, DEVICE data and TimeStamps”. Here an excerpt:

The Timestamp should indicate the time that the value and quality was obtained by the device (if this is available) or the time the server updated or validated the value and quality in its CACHE. Note that if a device or server is checking a value every 10 seconds then the expected behavior would be that the timestamp of that value would be updated every 10 seconds (even if the value is not actually changing). Thus the time stamp reflects the time at which the server knew the corresponding value was accurate.

Stefano Di Monte

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10/27/2017 - 00:52

Thanks a lot!

I found the same text in “Data Access Custom Interface Standard -Version 2.05A-” document, but I suppose this is an old specification.
How can I get the last version of OPC DA specification?

I am a member of OPC Foundation, but I don’t have permissions to download this kind of document.
Can you help me?

Thanks in advance,

Stefano

Guest

Guests

10/28/2017 - 05:39

The DA3.0 version is here: https://opcfoundation.org/deve…..ta-access/

It is a superset of 2.05A. So just using 2.05A you are good.

To download a specification you have to login. Make sure you login with the company eMail. If you are a member and not allowed to download after logging in I suggest you send an eMail to admin@opcfoundation.org. Specify the eMail you use to login and describe the behaviour.

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