Question: feedback loop for temperature control via peltier #562

I could really be misunderstanding still (sorry!)

Do you mean to simulate or do you want to drive an actual controller with input signals from sensors and output going to actuators?

Drive an actual peltier (in this particular case). I don't even think I can build a model for this, because I'm not trying to drive a single car, but many different cars (to use the metaphor of the cruise example). In this case, we're driving the peltier (no actuators) by setting the voltage.

But you still need to model what we call "the plant". How does your peltier element react to input of some sort (voltage) and how does it interact with the rest of the environment?

This is the part I'm still struggling with (and I'm not sure I want to try and model the incredibly non-linear portion of temperature propagating through various materials of different conductivities - unless that's what you're proposing?).

To clarify (including the "non-deterministic" part) -- we're cooling down a sensor-on-chip and the chip itself is performing scans to read out the sensor. Depending on the radioactive source in play, as well as the sensor performance and behavior, will heat up the entire chip. The goal of the PID controller would be to receive, as input, temperature of the system, and set the voltage of the peltier to some value in a range of [0, 5V], in order to achieve a setpoint temperature.

There's two things that (in my mind) make this different from the cruise example:

1. delayed response (the conductivity of these materials and how fast the temperature propagates is a function of the temperature of the system) where the peltier has to be driven a bit longer before seeing an impact on the temperature
2. thousands of chips+sensors will be placed in the housing [all with, of course, different behaviors which means different models] but the same software controller should still be able to cool down the chips to the setpoint temperature.

If you do say that this is possible, it would help if you could point me at something like FBS talking specifically about driving/controlling anything temperature-related. I can find many examples of mechanical systems involving speed/thrust/motion -- but I'm at a loss for anything temperature-related. If I was going to build a model, I'd need to do Finite-Element-Analysis for the thermal portions here in order to model it properly... Or am I somehow overcomplicating things?

In this case, we're driving the peltier (no actuators) by setting the voltage.

So the peltier is the actuator.

But I think I also misunderstood you or still do. Now it sounds like you are more looking for software to do realtime calculations including talking to the interfaces where you get the sensor inputs and set the peltier voltage output. Neither python-control nor MATLAB, which you mentioned are designed for that. (Although with some tweaks, Python or MATLAB may be abused for it)

To simulate anything, you need to model. The degree of approximation used for the model is at the discretion of the engineer. So is the choice of type of controller. It does not have to be a PID. A Bang-Bang controller would be even simpler to implement (but not to model). On the other hand, if robustness against different chip behaviors is key, you might even go overboard with the topic of "robust control".

But I think I also misunderstood you or still do. Now it sounds like you are more looking for software to do realtime calculations including talking to the interfaces where you get the sensor inputs and set the peltier voltage output. Neither python-control nor MATLAB, which you mentioned are designed for that. (Although with some tweaks, Python or MATLAB may be abused for it)

I think this is exactly what I want. Ok, I wasn't aware. I thought one could use python-control to actually drive something, but if it's purely a simulation-based tool [e.g. to understand exactly your system that you've modeled] then it's different than what I was looking for!

I think if I was to use the cruise metaphor (poorly), this would be like someone giving you a parking lot full of cars of various makes/models and various states of wear and tear -- and giving you the instruction: "give them all cruise control functionality". This probably answers my question then (sorry for misrepresenting it, as I'm not super familiar with the industry-specific jargon here).

Hi,

Maybe you should see this one:

https://github.com/robertobucher/pysimCoder

Best regards

josu

Thanks Josu! I will look into that. I found this one as well (https://github.com/m-lundberg/simple-pid/) so there seems to be examples I can look at.