Using another tag as the time parameter for TagVal()

Question

I am trying to create a tag that reports the value of tag A a number of minutes in the past determined by tag B. Tag B changes (it is a retention time).

TagVal('A', -'B')

Trying to do this throws the following error: Error -2147220186: Failed to retrieve events from server. [-15017] PIvalue Type is Not Allowed For This Call

I tried to circumvent this restriction by using TagAvg(), but the second time argument will only accept the current time '*'.

Does anyone know how I could make this work?

Community User · Accepted Answer

What are the units of retention time? If they are the number of minutes you could do something similar to the following to get the time:

'*'-'TagB'*60.

The above will get the start time back from now if tagB has the value in minutes.

Using another tag as the time parameter for TagVal()

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