Temp oscillation - Analysis needed

[merkur]

Hi - I have BrewPi running on a Raspberry Pi with the Arduino Uno and it is used to control my Fermentation Chamber which is a freezer. I am fermenting 5 gallon batched and the temp probe is in a thermowell in the center of the beer.

The heat source is a 250W ceramic heater. Typically control is +/- 0.5 degrees but the beer has just started a ramp-up in temperature and I am getting an oscillation of around +/- ).5 degree F. I believe that this can be optimized by tweaking the control parameters, but I am reluctant just to make changes without the full knowledge of what is happening.

All the settings are stock and I have been reluctant to change them.

Thanks. Screen captures below.

Paul

[Elco]

The integral is doing too much work and the proportional part too little. Increase Kp and decrease Ki.

[merkur]

Thanks Elco. I’am giving it a try.

Paul

[merkur]

Just to report back on this. I changed Kp to 6 and Ki to 0.2 and the oscillation settled out nicely as can be seen from the trace below.

Thanks for the quick response and good information.

Paul

[Elco]

I still think that the oscillation in your ramp is too much.
I would decrease Ki further and increase Kp more.

Something like Ki 0.05 and Kp 10.

[merkur]

Thanks Elco. Will give it a try.

[r_vandenbroek]

Hello! What a nice representation of the PID. Well, better than it is anyway. How did you get that onscreen?

CHeers, Rodge.

[merkur]

Hi Rodge - I used the standard Windows 10 ‘Snipping Tool’ to draw a box around the graph and then selected ‘Copy’ (Ctrl-C) and then went to the posting I was making on the BrewPi Forum and just pasted it into my message with Ctrl-V.

Quite easily done - for once!

All the best,

Paul

[j616s]

I think @r_vandenbroek means the screen for the parameters. I think the screenshot above is the legacy branch. The parameter view is different now.

[r_vandenbroek]

Yes, that is what I meant. My question wasn’t clear. Thanks!