Dual PID possible?

[ilgrank]

Hi
I was thinking of using a PID control on my oven, which has dual independent heating elements to control both upper and lower temperature.
I understand that is beyond the ESP32resso goal:.,in fact I wanted to kindly ask your opinion if it is something that can be done with some light modifications (I am not a programmer but I am able do some minor modifications to the code)
Thanks!

[Kolkman]

Interesting question.

I am not an expert either, but here is a (flow of) thought.

If you have two temperature sensors then you could have one control the upper and the other one the lower. There may be some interference on how the two PIDs converge. e.g. suppose that the lower element heats the upper part then the differential will probably suppress the power on the upper element. What could happen is that the whole system starts to oscillate. Given that the elements do not supply a negative force (cooling) I think that the odds of that are small, but it may have an influence on convergence.

If you have one sensor and two elements than I would have one pid drive both elements, perhaps with a power compensation if the two elements do not supply equal heating.

[Kolkman]

Oh.... as an additional thought: Whatever you do: don't rely on the ESP32 pid alone for runaway protection. My espresso machine has a second thermostat, that for the steam valve. That sets an upper limit to the heating. If you use this for your oven, you want to make sure that the upper limit of the temperature is controlled independently.
You don't want to have your house burned down because of a fault in the ESP or its software.

[ilgrank]

Hi
Thanks for your reply (sorry, I missed it initially)
You're right, I completely missed the fact that having two heat sources next to each other could lead to oscillations.. but given a second tought, I wonder if someone has already addressed the problem (in an open sourced project I mean) since I've recently seen a commercial oven with a single PID driving the two heating elements.
Guess for now the simplest (and most convenient) solution would be to use ESP32Resso as it is driving just the most critical (upper) heat source (the lower one has lots of thermal mass so it's easier to regulate manually)
Thanks again for your reply!