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Dears all,

Happy new year to all,

Today I have a discussion with our engineering team in our Petrochemical plant regarding implementing the square root in the Local field transmitter or in the DCS ((System))

Where is the best practice to implement the Square Root Function, in the Transmitter or System?

Please can any one advise what is the advantage and disadvantage for each principle, and what is the best from control point of view.

Your reply is highly appreciated.

BR

Happy new year to you also

Where to implement the square root?
I usually do it in the transmitter however it's been a long time since I purchased a DP flow device. I assume you are talking regular 4-20mA transmission. Suppose you had a 1% error in the 4-20mA signal. Would it make more difference before or after square root? Before I think especially at low flow rates. For Foundation Fieldbus it likely makes no difference where you do it except that the transmitter may have some special features that the DCS doesn't.

Good Question
Roy

Mathematically and from control point of view it doesn't make any significant difference EXCEPT:

1. putting the square root extraction in the transmitter unloads the DCS by one calculation, not very significant with today's processors.

2. for a compressible fluid, temperature and pressure compensation should be done before the square root extraction so unless the pressure and temperature devices are also part of the flow transmitter, then it is better to do the calculation in the DCS.