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How to properly totalize a flow tag

Question asked by jmgilman on Oct 9, 2015
Latest reply on Oct 12, 2015 by bala



I have an instantaneous flow tag in the units of GPM that I am trying to totalize over a 24 hour period. I'm attempting to use PI Datalink to obtain a month's worth of this totalized data. The issue I'm running into is the perceived inconsistencies I see within the data being returned.


For instance, I setup the following two Calculated Data queries:


  • Tag: Flow (GPM)
  • Time Interval: 1d
  • Conversion Factor: 1
  • Calculation Mode: average
  • Calculation basis: time-weighted
  • Expression Sampling: interpolated


  • Tag: Flow (GPM)
  • Time Interval: 1d
  • Conversion Factor: 1440
  • Calculation Mode: total
  • Calculation Basis: time-weighted
  • Expression Sampling: interpolated


Taken one day at random, I get the following data:


  • Average flow (first query): 46.67 GPM
  • Totalized flow (second query): 53,119.61 Gallons


Now, if we do the math: 46.67 * 1440 = 67,204.8 Gallons


Where did the extra 10,000+ gallons go? Isn't the total function just basically averaging the flow for the day and then multiplying by the conversion factor?


This particular data has legal requirements to be accurate and I would like to understand what the most accurate method is for totalizing a flow tag.