Temp oscillation - Analysis needed

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.


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

Thanks Elco. I’am giving it a try.


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.


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.

Thanks Elco. Will give it a try.

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

CHeers, Rodge.

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,


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.

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