Maybe I can help with the PID. Basics:
Lower I parameter (K_I) = integration of error has a larger effect
Lower D parameter (K_D) = response to changes is larger
Since you work with larg time scales you need large K_I and K_D to make everything slow and smooth. However, since you may also want to have a fast initial heat-up phase instead of having to wait lots of hours it could be best to use 2 sets of parameters, maybe whatever you use to controll has such a option. Otherwise you can (maybe) change the parameters while the system is running or just turn it off and change them after it reached the target temperature.
What were the parameters with oscillations? With the highest possible K_P with stable oscillation you can calculate good starting points for the parameters.
Ziegler–Nichols methodWhy im actually here: I want to measure temperature with high precision and resolution (0.1 mK). Regarding the signal processing: Is the
LTC2983 good or the best? I would buy the whole
evaluation kit and use that.
Any recommendations regarding the sensor? I would prefer Pt1000, but maybe thats nonsense?
What about tolerance? B 1/10 has a max. error of +-1.55°C at 250°C. Doesnt really blow me away. Even AA is +- 0.525°C at 250°C.
Are there easy temperature-references to check things? The triple point of water is a option as well as the meltingpoint of highly pure gallium. What about higher temperatures? Melting point of pure tin/lead/...? How accurate is that? Can I reliably check for absolute precision like that?
There is also the question about linearization parameters [the f in T = f(R)], they only need to be a little bit off to introduce a lot of error. Are they known to be good enough?
Now keep in mind that I want to stay well below 500 € with the thermometer. The 200 € for said evaluation kit is already a lot. I dont need to get the very last bit of precision, but I would need a way to verify it. 1°C off at 250°C is no problem, I just need to know about it.
I have a reference thermometer that was NIST-traceable calibrated until 2018 and had ~1mK error according to the cerfiticate. A quick test with a pure water ice-bath (at 1020mbar in a dewar) resulted in a reading of -0.0043°C averaged over a duration of 4h (0.7mK standard deviation). But I was unable to find a high resolution melting temperature of water ice (Ih). All I found were some models etc. and how they didnt really get it right. They didnt mentioned the melting point with high resolution since they were off >>1°C anyway.