Emerson Exchange 365

How to disable integral action (RESET) to get a Proportional-Only Controller

Dear experts here,

Currently I am working on a Closed-Loop Setpoint Response tuning method which need me to switch the PID controller to Proportional-Only. What is the right method to get this type of controller? Set the RESET to 0 in order to disable the integral? Or is it necessary to change the STRUCTURE parameter at the PID block to "P on Error, D on PV"? Currently at DCS, the settings is "PI on Error, D on PV". I tried to change the settings into "P on Error, D on PV" to disable the integral action. But when I turn the controller from manual to Auto, suddenly the controller output goes to zero. It caused an upset to the process. I am not sure what is the problem, because before this no such problem occurred in the plant. Can anyone here provide me the correct procedure to get the P-Only controller? Thank You.

Haris Badrul

• 19 Sep 2016 7:17 AM
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18 Replies

• Jean-Marc Dufert

  

  • 15 Jun 2021 11:44 AM

  Haris,
  
  I had the same problem, if you have a pid structure, you don't know how to cancel the i, neither by 0, nor by 9999, nor by 99999, which I was told.
  To make tests in pure P, it is obligatory to put the structure PD with d = 0. The pid with I = 0 or = infinite, will nevertheless integrate. I made a PID block alone, to simulate and we see the output integrate little by little with an i at zero!
  Today, I have no other solution!
  
  Jean-Marc

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• James Beall

  

  • 15 Jun 2021 12:51 PM

  Haris,
  The PD Structure with D=0 should be a P only controller. Any PID structure will have some Integral, it is not "turned off" with 0 (this is very fast integral) nor a very large number though a large number like 999999 makes it VERY slow. When I used either of the two PD structures, I got the output bump as you did when I switched from Manual to Auto. However, I selected the PID/ControlOpt "Act on IR" and the bump did not happen. I will check into this in more detail and let you know.
  James

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• James Beall

  

  • 15 Jun 2021 12:56 PM

  In reply to James Beall:

  Haris,
  I noticed that "Act on IR" (initialization request) made the PID/BIAS parameter to automatically adjust as needed (OUT=P*errror + Bias) to prevent the bump.
  James

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