Hello All,

We have created a calculation in PI PE. The calculation computes the difference in values for a source tag at 8 AM current day and 8AM previous day.

We have created the calculation in PE using tagVal function. The expression is as below.

**TagVal(tag1, 't+8h') - TagVal (tag1, 'y+8h')**

tag1 is the source tag that does not have values exactly at 8AM. So the PE returns results based on the interpolated value.

The calculation was previously performed in Datalink using ArcVal function and Auto retrieval mode. The results of PE and Datalink do not match.

We have tried using interpolated retrieval mode in datalink and still the results do not match. Please let us know why the interpolated values of the source tag at 8 AM do not match between PE and Datalink.

Please let us know for any additional details.

Thanks,

Nandhini.S

If you evaluate the expression in PI SMT>Points>Perofmrance Equations>Equation>paste in your equation and hit evaluate, do you get the same value as PI Datalink?

How is your PE scheduled to run? What time does it actually calculate? In PI Datalink is the Timestamp parameter the same as the day on which the PE was run? Be sure to turn on timestamps in PI Datalink so you can verify the expression is evaluated on the correct day.