When the tunings are changed, it might be good to reset the integrals. about arduino-pid-library HOT 9 OPEN

Setting a high proportional constant (e.g. Kp=255, Kp=1e6...) makes the proportional band narrow, and then PID acts like bang-bang because either kPerror>outMax or kPerror<outMin.

Looks like AutoPID doesn't do anything at all to limit the integral:

https://github.com/r-downing/AutoPID/blob/fea6b99a4f05f2b53669d684fae6fe09b5391754/AutoPID.cpp#L43-L69

Maybe it behaves as a sort of conditional integration, where integration is depends on being within the band.

AutoPID does expose the integral, so a user could periodically check if it was wound up above outMax or outMax-error*Kp, etc., and reset it as desired.

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I was playing around with it and added a SetIntegral(double) and GetIntegral(double) in this sample at Wokwi:

https://wokwi.com/projects/358122536159671297

(If you play with it, be sure to toggle the SerialMonitor/SerialPlotter graph icon in the lower right corner.

I added a pull request: #132

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will be taken care of in the next task cycle, no need to duplicate code.

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Why? If you don't reset the integral, then the tuning changes should be bumpless, per http://brettbeauregard.com/blog/2017/06/proportional-on-measurement-the-code/ and http://brettbeauregard.com/blog/2011/04/improving-the-beginner%e2%80%99s-pid-tuning-changes/

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In my case, resetting the integral helped a lot, it reduced the overshoot a lot.

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Is this issue about overshoot? Or is it about SetTunings? I can't imagine the use-case for making SetTunings non- bumpless. I often operate heaters with PV far from zero, and resetting the integral to zero in SetTuning() would induce a bump.

If overshoot, I could see doing an integral reset to zero when crossing into the proportional zone at (SP-PV)>=outMax/kP.

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I used two parameters and they are toggled when the input is close to the setpoint.

Below 2.5 degrees uses a softer parameter, above 2.5 degrees difference uses a more aggressive parameter.

I saw an additional function in another library, maybe it's related to this behavior.

AutoPID::setBangBang

Ref.: AutoPID

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A smaller change to the library than #132 adding functions is to move the PID_v1.h:: outputSum variable from private up to public, which enables all sorts user-space tricks.

PR #133 -- Expose integral to enable user-space hacking:

It has a live example at https://wokwi.com/projects/358190033668210689

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