Hi,
Recently within the team, we’ve been a bit confused about the difference between the historic and basic tag groups. Could someone please confirm whether data collection is performed independently for both tag groups?
We’re considering the following scenario: we assign tags to the basic tag group for leased polling, to poll the PLC at a 1-second interval when the tags are displayed in the client. At the same time, we collect the same data to the historian with a 5-second polling rate.
If the tag groups operate independently, then I would expect this behavior:
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If a tag is not displayed anywhere, it is polled with a 5-second interval.
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If a tag is displayed in the client, it is polled with a 1-second interval.
I’d appreciate any thoughts or guidance you can share on whether this is accurate (and, if not, what the expected behaviour would be).
Thank you!
Hi there,
The tag group of a tag is determine how the tag is updated. With the leased tag group (1 second for displayed tags and 5 seconds for not displayed tags) it will update as you expect.
However, historization is another matter.
Using Tag Historian it obeys the Sample Mode for when to historize the data point.
If you want it to historize the data similar to how it is updated in the leased tag group you would need to select the Tag Group under Sample Mode and then select the leased tag group under the Historical Tag Group.
The Periodic Sample Mode will always regardless of any value change store a value at the selected sample rate.
The On-Change Mode will only store the value when the value is changing outside the specified deadband. In the case where the tag itself is following the leased tag group the On-change mode validate the change based on that group. But it might not necessarily store a value if it is not outside the deadband.
In your case with the polling mode as the Sample Mode it will always store a value every 5 seconds regardless if the tag is displayed or not. You should select Tag Group or On-Change if you want it to follow the behaviour as the real time tag updates.
Just to clarify: I want to configure a single tag. In the Basic tag group settings, I configured the tag as “Leased”, which should poll with a 1-second interval when the tag is displayed.
In parallel, in the History section, I configured Sample mode = Tag group and set the Historical tag group to “Historical” with a 5-second polling rate.
My question is: will these two collections work independently, meaning the historian will collect the tag value at a 5-second interval regardless of whether the tag is displayed (while the basic leased polling switches to 1-second only when displayed)?
If not, could you please confirm what the expected behaviour is?
Kind regards