Using PID with a TC4

[Erichimedes]

Hi all, and thanks so much for your work on Artisan! I've used it for years to log/control my roasts via alarms but I want to try to set up PID control with the new features in 3.4. Roaster is a self build fluid bed, with a TC4 that connects heat and fan control from the roaster to Artisan. I'd like to control Environment temp.

The problem I'm having is there seems to be some kind of issue when I turn on PID, as it just usually locks up at 25% heat power. It seems to do this when the I value goes to 100. No idea why it's doing that, and if I turn it off, then back on, the I value doesn't reset, it just stays wherever it was. Here are my settings:

Please ignore the Mode: Background, since I do actually have it in Mode: Manual for testing purposes.

[Terracotta-6]

Possible Cause Analysis:

Integral Windup:

The I value reaching 100 is likely a symptom of integral windup: when a persistent error exists over an extended period (e.g., the setpoint is significantly higher than the current temperature), the integral term accumulates continuously, causing the output to become "stuck."

Solution: Enable an anti-windup mechanism or impose a maximum limit on the integral term.

Inappropriate PID Parameters:

Default or arbitrarily chosen P, I, and D values may cause system oscillation or sluggish response.

In particular, an excessively high I value can worsen integral windup.

Output Limitation Error？
Positive ，Clamp 50.

[Erichimedes]

It's definitely integral windup, the question is why is it happening. The P, I and D parameters are not chosen arbitrarily, they worked well in previous Artisan versions. I is also not excessively high, and it does the same thing no matter what values are entered. Something else is wrong, and it happened when I updated to the latest version of Artisan this morning

[MAKOMO]

You did add an output limit of 50% and a duty (mapping limit to 50%) of this. This results in a max burner slider output of max 25%. Set both to max 100%. If you want the integral term to reset on SP changes you need to tick IRoC and set an appropriate SP limit.

[Erichimedes]

This was it! Thanks for catching that. It unlocked the system and I was able to go about tuning PID parameters correctly. Even did my first PID controlled roast and it was better than I ever could have hoped for.
I don't understand anything in the Config box, that's all new. Is there anywhere I could read about those parameters to understand them better?
Also, when the PID is running and following a background profile, I see that the P, D and PID Error monitors usually just show u.u instead of a value. I'd love to understand that a bit more too.

Thanks again very much