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Advises on programming/tuning a PID for Peltier element
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perieanuo:
I had in a company I worked a module for a peltier that did reverse temperature control (heating or cooling), the output stage was triacs with moc's (and a second variant with mosfets, that one was    Ok too) the micro msp 432 something, an lcd and some switches attached and as sensor we had analog parametrable input (lm72 if I remember correctly).The limitation was the sensor to 115 deg C but as sensor was parametrable it was adaptable(the project focused on 37 deg C as middle temp).
Beside the power heating/cooling comming from peltier type solution, the idea is not bad.
The PID was configurable via PC app to adapt to different heat capacity and peltier modules.
Me, I was using it to preheat pcb-s combined with hotair soldering or for big radiators (later I replaced with an arduino with thermocouple amplifier for raising the temp ).
I don't have the code for the pid...but it was stable with the Derivative part too (I usually tune mostly the P and I part).
I love triac style cause of EEM stuff but for hobby cost decides.
Regards,Pierre


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arronar:

--- Quote from: chemelec on November 22, 2018, 05:44:59 pm ---I use Mosfets to turn them on and Off.

--- End quote ---

I thought that too but I wasn't sure that there are MOSFETs that can afford the currents and voltages that a Peltier consumes. Can you describe the way you follow to choose a proper MOSFET to use?
rstofer:

--- Quote from: arronar on November 23, 2018, 10:39:01 am ---
--- Quote from: chemelec on November 22, 2018, 05:44:59 pm ---I use Mosfets to turn them on and Off.

--- End quote ---

I thought that too but I wasn't sure that there are MOSFETs that can afford the currents and voltages that a Peltier consumes. Can you describe the way you follow to choose a proper MOSFET to use?

--- End quote ---

Perhaps a link to the actual Peltier?  If there is some kind of commercial controller, perhaps a link to that?  Since there are MOSFETs working up to hundreds of amps and quite high voltage, I suspect they will work quite well. The fact that this setup requires a servo type pulse is puzzling (to me).

I got rather too interested in this project, more specifically, control systems in general.  In watching the Brian Douglas videos, he plays around with heating and PID.  He uses this gadget for the demo board and links it to MATLAB but it also has Python code.  Lots of Python code...

http://apmonitor.com/pdc/index.php/Main/ArduinoTemperatureControl

For $35 out of Amazon, it is quite useful.  Among other things there is a PID control loop written in Python and the results of set point and temperature are displayed on a nice chart along with captured data in a file.

You really can't get very far with control constants without knowing step response of the system.  You already have a start on that with your data file.

A simplified approach that doesn't include Derivative, similar in concept to Ziegler-Nichols but here the presenter gets time constants from the step response curve.




Vtile:

--- Quote from: rstofer on November 24, 2018, 10:41:03 pm ---
--- Quote from: arronar on November 23, 2018, 10:39:01 am ---
--- Quote from: chemelec on November 22, 2018, 05:44:59 pm ---I use Mosfets to turn them on and Off.

--- End quote ---

I thought that too but I wasn't sure that there are MOSFETs that can afford the currents and voltages that a Peltier consumes. Can you describe the way you follow to choose a proper MOSFET to use?

--- End quote ---

Perhaps a link to the actual Peltier?  If there is some kind of commercial controller, perhaps a link to that?  Since there are MOSFETs working up to hundreds of amps and quite high voltage, I suspect they will work quite well. The fact that this setup requires a servo type pulse is puzzling (to me).

I got rather too interested in this project, more specifically, control systems in general.  In watching the Brian Douglas videos, he plays around with heating and PID.  He uses this gadget for the demo board and links it to MATLAB but it also has Python code.  Lots of Python code...

http://apmonitor.com/pdc/index.php/Main/ArduinoTemperatureControl

For $35 out of Amazon, it is quite useful.  Among other things there is a PID control loop written in Python and the results of set point and temperature are displayed on a nice chart along with captured data in a file.

You really can't get very far with control constants without knowing step response of the system.  You already have a start on that with your data file.

A simplified approach that doesn't include Derivative, similar in concept to Ziegler-Nichols but here the presenter gets time constants from the step response curve.



--- End quote ---
Yes. That is coined also as Ziegler-Nichols, but step response (or closed loop) method I were referring earlier. Much better in general than the Ziegler-Nichols open loop / oscillation method. There is lots of variations (the coefficient multipliers) for this closed loop response method. Also many PID autotuning methods are rather simple algorithms and use open loop tuning, might be interesting to take a peek...
rstofer:
Attached is the graphical output of the Python PID controller test program for that TemperatureLab gadget I talked about in Reply #17.  I have left the coefficients as given.
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