Hi
I define a tag expression with now(0) as expression.
The problem is the value of tag in update in every second with current time. When I set now(0) it should mean it only run only once. why my tag value update every second?
Even i try to use change scan class to 10 s but it always updated every second.
I can’t imagine it would be useful as a gateway tag. Did you try it as a client tag?
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I believe the poll rate of the now() expression tag only is meaningful within Vision scripts (not tags, in tags it follows the execution mode or scan class). EDIT: Also possibly Client Tags, @JordanCClark might be right on that.
I just tested this behavior under 8.0.2 with a tag configured with execution mode of “Tag Group” (so that it respects the configured Tag Group/Scan Class).
It was updating once per second as expected with the Default scan class. However, changing the scan class from Default to Slow (a Direct scan class I created with 10000ms rate) did not result in a change in update times. Only when I copied, deleted, and re-pasted the tag did it start to update at the expected 10000ms rate. This might be an issue in 8.0.2.
I also tested this under 7.9.12 with a similar tag configuration and changing the scan class and applying the changes to the tag had the expected results (tag updated per the configured scan class).
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It sounds like the tags scan class/tag group is overriding the now(0) .
There is similar behavior when using runScript() in tags.
snippet:
link: runScript()
I would look into using a different scan class/tag group for that tag(s) to suit your needs.
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The scanclass triggler the now() if I use tag in gateway. Even with now(10000). Hope IA fix this bug.
Not a bug. Documented behavior. Same for runScript in a tag expression. There’s new functionality (that I haven’t used yet) in v8 that addresses this.
What would the use case be for using now(0) in the gateway?
I just try to create a timer event in tag change event with now(1000) for every second but it didn’t work so try now(0) to see if scan class really trigger the tag change event.
