Some PI Excel formulas allow interpolated values to be returned in addition to those archive values actually stored in the Historian database. Having tried to use this today I have hit a snag that I thought should be shared.

Say we have two time/value pairs in PI:

10:00:00 / 5MW
10:30:00 / 10MW

Interpolated should (I believe) return a point ON the line between those two points. So if an interpolated archive value is requested at 10:15:00 you would expect to get an answer of 7.5MW! However I noticed that the a value corresponding to 10:00:00 (i.e. 5MW) was being returned. The PI Help pages for Archive Value clarify matters:

“Interpolated - Interpolates the value at the specified timestamp except for ... tags with step attribute set .... For this special case, the previous value is simply carried forward.”

As all of our tags are configured with the step attribute set we cannot currently utilise the interpolated method of retrieving data.

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Intersting point about getting PI data into MS Word. I wonder if there are there other applications that that would work with?

Don't yet use the SMT (use the Beaver Valley Tag Manager) but looking forward to it's bulk editing capabiltiy when we move to the MDB. We'll have to consider the 'Step' question later. :-)