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PI Vision Calculations

Martin.Wildeman

When I create a calculation for total flow from a well (in this case) the calculation continuously changes with no flow.

The calculation looks like this:

tagtot('GlenH1W.Prcs.FT_StnDchrg','1-jan-13','*')*1440

The tag is the well flow meter in gpm and it is set in the PLC to be zero when the pump run status is "OFF".

1-Jan-13 is the beginning of my archive

The resultant value changes every 5 seconds to a lower number with no pump run. Why?

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    As the PI Vision documentation says, "Expressions that require a specified time interval are not supported." see the bottom of Calculation syntax

    This is to prevent your display from freezing up from a long archive call.

    For such a long calculation, you should implement it as an analysis and write the result to a PI tag, then use that tag in PI Vision. You should not be dynamically asking for a total of 12+ years of data every time a display is loaded.