[sdiy] Ways of simulating thermal drift and stabilization?

Spiros Makris spirosmakris92 at gmail.com
Sun Apr 18 11:37:57 CEST 2021


Hello list,
I know this is far fetched, but is there a method to simulate temperature
effects in circuits? Specifically, I would like to look closer to oven
stabilization, which I have implemented before, but designed on a
completely empirical level.
That is, I first tried on/of control (opamp with no feedback), then I tried
simple proportional control and finally added a capacitor to reduce the
loop bandwidth, all on the breadboard, with 15-20 minutes required for each
experiment, and it was fairly hard to visualise the data (looking for a
30-50mV signal on a scope over the course of 20 minutes...).
Are there any realistic alternatives to trial and error? Could SPICE do
such a thing? Or perhaps are there some thermal models I could load up in
Matlab and design a controller around it? I don't know enough about control
to extract these by experimenting, but I think I can handle it if there's
some transfer functions already available for me to play with.

Just for reference, I attach the circuit I came up with last time, and its
measured output during power up. To calibrate, the circuit is first powered
with heat enable disconnected, and the voltage of the diode connected
transistor is measured. The voltage of T_ref is set 50mV or so above that,
then heater enable is connected. This sets the operating point at 50C or so.
This module has a couple of rookie mistakes, such as using the rails
directly as voltage references, but I think they are irrelevant to the
question itself so let's try to ignore them 😂

[image: image.png]
[image: image.png]

On off control
[image: image.png]
Opamp output at startup
[image: image.png]
opamp output at steady state
[image: image.png]

it's interesting that this waveform was 80hz or so, and the duty cycle was
depended on the temperature reference. Touching the chip (therefore
changing its thermal properties) changed this frequency.
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