Hi,
Why would my OPC tag with history enabled get a sample every second if the value doesn't change?
As long as I don't have Max Time Between Samples configured, I would not expect multiple samples with the same value. Is there anything I am missing? The table is populated with As Stored so there is not interpolation...
Thanks.
Daniel.
I think you do have Max Time Between Samples configured. A value of zero is not "not configured". You've told it zero delay - so record the tag value at the polling rate, which I assume is default and set to 1000 ms. [This is incorrect. See Chris_Bingham's docs reference in post #5 below.]
Instead change it to a value that ensures you get at least one reading in every period of likely interest. This will avoid problems when you select a timespan when no changes were recorded.
You can also get multiple collections of the same value if the OPC quality on the tag is changing.
Thank you Transistor and Steve! Solved.
You were both right. I didn't realize 0 does not mean "nothing" in Max Time Between Sample. And this was basically choking the OPC which kept changing quality from Good to Good Overload, and this also explains what Steve mentioned.
It seems to be good now and I took Transistor's advice to have a Max time also to guarantee some data in the historian...
From: Tag Properties | Ignition User Manual
Max Time Between Samples
"Setting this value to 0 will disable automatic record collection. Default is 0."
@Daniel_Calderon, what version of Ignition?
What is the data type of the tag?
What are the specifics of the tag group you are using?
Thanks for the correction, Chris. I need to read it a few more times to see if I understand it now.
No problem. I still like your recommendation to set a reasonable value. 1/hour, 1/day…whatever makes sense to collect “as little data as possible for that point, but no less…”
I suspect that @Steve_Laubach was correct, in that tag quality might be contributing excess data.
^^^ @Daniel_Calderon - This is worth investigating further ^^^
Though, perhaps data type is a float, we’re not seeing the truncated data (additional decimal places), and compression settings (absolute @ 0.01) are working as expected?
Chris thanks for the correction. Good to know.
The type is integer and I moved them all to 10 sec poll rate and now they are always GOOD and not repeating values. I think root cause was quality status changing, I saw an older post
I am running 8.1.45.
