Help with tuning PID conical

1

For a while now I am struggling with tuning my PID for my conical. The conical is a SS brewtech ½ bbl heated with the heating pad from SS brewtech and cooled with a home made glycol cooler. Temperature of the cooling water is 2 degrees.

Hopefully somebody can help me out.

If more information is needed or more detailed graphs please let me know!

Settings that I have now:

Cooling minimum ON period 2seconds
Cool PWM period 10minutes
Heat PWM period 10 seconds
Mutex heater and cooling is 2hour
Cool PID P -10 Ti 2h Td 10m
Heat PID Kp -50 Ti 2h Td 10m

Screenshot of beer temperature with actuators and PWM

graph (11)
graph (11)3000×1500 275 KB

Screenshot with PID of heater and cooler

graph (12)
graph (12)3000×1500 325 KB

2

Is this correct? It looks like you wrote out cool settings twice.

This is very long for a glycol setup. Depending on your system, 5-15m is more appropriate.

I suspect the temperature swings will be smoother already with a shorter mutex lockout. With that noise eliminated, we can further finetune PID settings.

3

oh my bad. The Kp is 50 for the heater. The rest is the same.

I set the mutex so long because I have a overshoot. Without that it was constantly heating and cooling. At the moment I am fermenting 50 liters of IPA. If I now set the mutex at 15 minutes the beer is constantly cooled and heated etc. I dont want that. Maybe wait untill fermentation is finished and do a testrun with water.

4

The PIDs keep building up output during the lockout, and then have react more heavily. This makes it harder to see what’s going on.
When to tune is up to you. The temp variance right now (~0.3C) is not terrible, merely suboptimal.

5

Ah that makes sense. I set the mutex to 15 min for the heater and cooler. Now wait and see what happens.

6

I disagree with Bob here. Mutex between heating and cooling of 2 hours sounds fine. The problem is overshooting the cooling.

Can you show the PID widget graph of both PIDs?
I think reducing Kp for the cooler is what’s needed.
And set Ti to 6h for both. It seems to take a few hours for the process to respond to heating, the integral time constant (Ti) should be a multiple of the process time constant. Perhaps even 12h for you.

Heating more gently too might help, with Kp at 25.

My conical is within 0.1 degrees, with the SS Brewtech heat pad.