Hello,
I have a level controller PID and its doing this:
Why when I set the PID Parameter STRUCTURE to PID Action on Error or PI Action on Error, D Action on PV , and MODE to auto, the output does not control the setpoint? The output swings from 15 to 45% (because I have low and high output limits of 15 and 45%).
However when I set PID Parameter STRUCTURE to P Action on Error, D Action on PV , AUTO the loop controls setpoint.
I would like to set the structure to PI Action on Error, D Action on PV, but when I do, output drops to 15%.
Anyone help would be great.
http://i.imgur.com/7Prj6Ai.png tuning parameters
http://i.imgur.com/nSdOUaR.png loop when in PI Action on Error, D Action on PV
Below is picture of working in P Action on Error, D Action on PV ok, but I want to use PI Action on Error, D Action on PV because this is level control.
In reply to Steve Elves:
Thank you Steve, This is helpful to know. This makes sense. If reset was higher, it would slowly decrease and not just jump to low and high limits. Do I need to set the structure back to PID Action on Error and then retune the loop?
In reply to Lou Heavner:
Thank you Lou for responding.
This control level loop will often (maybe once or twice a month) experience be needed to control at multiple set-points (60% 65%,77%, 80%, 84%, etc.) depending on production needs. Also at times, the product in the tank will be different at times.
Yes, I do not need D action. I will use Tune with Insight On Demand system, and set to PI control. I will set the structure to PI Action on Error, D Action on PV
Currently the tuning is stable with the attached results, but PV and SP has a bit of offset.
In reply to Carlos Velazquez:
Thanks Carlos,
We have a few level loops set for PI and the D is at 0. Yes, I am changing to PI.
Thanks
In reply to DCS Newbie:
As has been mentioned, the problem appears to be that the integral action (Reset) is much too fast (1.5 seconds). The reason it is stable with the "P action on Error and D on PV" is that the integral action is turned off. As Lou Heaver suggests, you should use Lambda tuning for this "integrating process" of the level. Try a Reset time of 600 seconds (or larger) to slow down the integral action. The structure you desire to use will work fine. For more information on Lambda tuning for integrating processes, see this article in ISA Intech magazine "Loop tuning basics: Integrating processes" - https://www.isa.org/intech/201604basics/ Hope this helps!James