1 Reply Latest reply on Jul 11, 2018 9:36 PM by jru

# PI performances equations

Hi all;

I have a problem with the
PI process book, I need to run an equation whose result is summed for
every minute; Here is the syntax: (Tagval ('flowrate','t+1m')-Tagval ('flowrate','t'))*Tagval ('density','t+1m)

In addition, I need to sum up this result for every minute until 24h achieved.

I wonder if there is any solution in PI process book using performances equation, to solve the nested series problem .

I have tried to do it in the hard way by writing all the algorithm in PI calculation range, but there was a problem of having all the equations written down.(It mentions "calcul failed " after having 18 syntax written).

Thank you so much

• ###### Re: PI performances equations

Hi Ranim,

I apologize for the slow response rate.  If you were able to find an appropriate solution for your use case, please feel free to let us know.  In the meantime, here are some of my thoughts on the matter.

First of, based on the syntax of the formula you are using, it looks like you are trying to calculate the change in volumetric flow in the span of that minute.  And you would like to totalize that measurement over the course of 1 day.

Based on the formulaic complexity of this calculation, I'd recommend that you create a PI Performance Equation Tag or PI Calculation with the following syntax:  (TagVal('FlowRate','*') - TagVal('FlowRate','*-1m'))*TagVal('Density','*')

Then you can use the Total data retrieval method with a calculation interval of 24 hours to get your desired result.

If you want to use a running total for the day, you'll need to use a PI Performance Equation so that you can historize the results of your volumetric change calculation to a PI Tag and use a Totalizer tag or another PI Performance Equation Tag or PI Calculation with the syntax: TagTot('VolumeChange','t','*') to get that result.  Bear in mind that this requires you to use a PI Performance Equation tag for your volumetric change calculation as you are not able to reference a PI Calculation in another PI Calculation.

If I misunderstood your use case, please feel free to let me know what your end goal is.

~Jesse

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