Emerson Exchange 365

Getting Proportional Kick in PID controller when I shouldn't

Hello,

I've noticed that I am getting a proportional kick in some PID controllers which have the structure: "I action on error, PD action on PV". This structure sets BETA = 0 which means I should get no kick.

Any ideas on what am I missing?

I have other PID controllers with no proportional kick on SP change with the "I action on error, PD action on PV" structure.

Thanks

Richard Hadidian

• 23 Jul 2018 6:09 PM
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2 Replies

• James Beall

  

  • 23 Jul 2018 7:56 PM

  Do you have happen to be using the FRSIPID "Non-linear Gain" Option? I have not tested this statement on V12 or V13, but V11 and prior, "If the Non-linear Gain option is enabled, the “P” action will always be applied to the Error, not PV, regardless of the PID Structure chosen (including 2 degrees of freedom). So if you move the SP such that the error is outside of NL_GAP+NL_HYST, there will be a “proportional kick” of the output".

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• Richard Hadidian

  

  • 23 Jul 2018 8:28 PM

  In reply to James Beall:

  Thank you James, Yes, it was the non-linear gain option. I just tested two controllers. One Temperature controller with no FRSIPID, and indeed there was no kick. Then tested a Level controller with FRSIPID and the only difference is that no matter what SP change I make (even when the error is still within NL_GAP) I still get the proportional kick (mind you, it is the MINMOD proportional kick, so it is a smaller one)
  
  Thank you again James,
  
  Richard

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