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Calculation function in DeltaV

Hello Everyone

A few years ago, I created a calculation tag in our PI system with a few functions like

Tagval (Tag number, Time): the value of the tag at that time 

Tagmax (Tag number, Start time, End time): max value of the tag

Prevval (Tag number): quote previous value of the tag

FindEq (Tag number, Start time, End time, Value): return the time when the tag value is equal to the value within the time specified.

I have tried to make same equation using above functions in DeltaV, but I couldn't figure out how to achieve the same result. 

Are there any functions of calculation in DeltaV I can use like the functions above?

Junggyu Yu

• 13 Aug 2020 1:20 AM
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6 Replies

• Michael Moody

  

  • 13 Aug 2020 2:34 PM

  For the PI system examples, were you using Performance Equations or ACE (Advance Calcs)? Those are purpose built functions.
  
  We've definitely had cases where we concatenated values (strings, floats, integers, etc.) into a single parameter - usually for display. I see no reason that time cannot be one of the components. These parameters can be collected in the DeltaV Historian if that is what you are asking.
  
  Can you explain your use case?
  Based on your PI system examples, are you updating Tagval based on a trigger?

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• Lun.Raznik

  

  • 13 Aug 2020 2:59 PM

  In reply to Michael Moody:

  This is not the same but this can be implemeted in DeltaV Excel Addin. Once the data is in Excel then imagination is the limit.

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• LaurentB

  

  • 13 Aug 2020 3:20 PM

  In reply to Lun.Raznik:

  I think DeltaV Excel reporter is more appropriate to build these advanced functions and already have some interesting calculation function ( use Configure Calculate data functions
  
  (Minimum value (including the following meta data: timestamp, parameter status, and/or collection status)
  Maximum value (including the following meta data: timestamp, parameter status, and/or collection status)
  Time average value
  Average value
  Total value
  Range value
  Standard deviation value
  Count of raw sample value
  Percent history available value
  Percent Ff status good value
  Percent Ff status not limited value
  Percent Ff status not bad value
  Composite parameter status
  Composite collection status )
  
  When data are into Excel cells that's easy to add powerfull calculation on them

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• Junggyu Yu

  

  • 14 Aug 2020 1:02 AM

  In reply to Michael Moody:

  Hi Micheal

  Thanks for your interest. I am not sure if you can clearly see the equations I used in our PI system. If you want I can send the image through your e-mail.

  According to our dryer regeneration operation principle, monitoring heat bump to see residual heat after regeneration of drier beds are important factor.

  However the direct temperature reading is not the ultimate indicator. The heat bump between the temperature when the rate of temperature change is increased and the max temperature is what we want to ultimately monitor to verify regeneration condition of driers.

  

  With the set of 4 calculation tags with temperature reading, I could get the magnitude of heat bump in PI historian.

  You can see the temperature reading(Green) and the heat bump(Black) in the trend below. As PI is not shown in our DeltaV, I wanted to make same calculations before, but I couldn't figure out how to do it. 

  If you can let me know the method, it will be very appreciated.

  

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• Junggyu Yu

  

  • 14 Aug 2020 1:03 AM

  In reply to Lun.Raznik:

  Thanks for your comment. You are right the excel Addin would have similar functions from historian. But I would like to make the real time calculation tags in the DeltaV. Can it be done as well?

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• Lun.Raznik

  

  • 17 Aug 2020 9:54 PM

  In reply to Junggyu Yu:

  By the way, some of the calculations can be done using OPC HDA as well using aggregate functions. If the aggregate functions does not provide what is needed, data can be read using ReadRaw and perform calculations based on that data.

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