That the thing i did about week ago:
R6 - 10K thermistor, 5K around +32C, it makes around -1Kohm / 1C slope
2x2K - hooked to hp3456 to measure temp deviation, in sequence resistance changing around -75 ohm / 1C , at 33 C
thermistors from aliexpress, defined as MF58.
heater 2 mosfets, pick 2 from around 6 with close characteristics, mounted on opposite side.
when ON consumed 200ma total, around 1 sec on, 5 sec off, cycle. ( the hysteresis produce very small level of a temperature jumping, thermistor sensor changing at 0.15 ohm much less then 0.001 C )
the whole board tossed inside the case, so it relatively stable ....
What I'm observing:
assuming 2x2K thermistors are stable - my resistance deviation for 6 hours 2 ohm == 0.05 C; over 24h == 8 ohm -> 0.1 C
and drifting per day approx. 0.08C, it drift up and down, around 0.2-0.3 C per week. ( i had just a week of running)
when I use single 2K thermistor, (1K at +43C) due to much less slope i had 0.3C per day stability.
it basically my first attempt, so I wonder:
about overall direction, are thermistors as sensors are stable enought, or I should think about to use diode instead ...
2K and 10K - has a differ material , guess, in my understanding, wonder if 2k are more stable, then schematic need a change to sense much less slope, same for diode.
To decrease hysteresis more , i'm thinking a rectangular aluminium plate , drill a hole for thermistors or diode , and use it between heaters and the frame,
also thinking 2 transistors, but only 1 are monitoring it may produce more uncertainties ... so to change to one transistor only,
And I didn't count a self-heating effect of thermistors at all - even don't know if it matter ( when I manually switch resistance range on HP, a diff voltage apply, and self heating was very-very visible)
So here we go again ... assumed it was a finger snap but .... like ... drifting a 2C per year - at the best , it will spoil everything ...
schematic:
the box:
10K thermistor as sensor:
2k thermistors: