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Topic: Increasing thermistor accuracy (Read 975 times) previous topic - next topic

kendreaditya

#60
Nov 14, 2019, 11:36 pm Last Edit: Nov 15, 2019, 12:43 am by kendreaditya
Look up a resistance vs. temperature table for your NTC (or any NTC for that matter).
Use it to calibrate the Steinhart-Hart equation (it can't get better than that).
Plot them both, and see how much they deviate.
So I did that and resistance and temperatures were very close:

NTC table:
20.80   11,868.8
20.85   11,844.3
20.90   11,819.9

My NTC thermistor values with Steinhart:
20.819 C
11858.97 ohm

NTC table:
59.30   2,825.33
59.35   2,820.58
59.40   2,815.84

My NTC thermistor values with Steinhart:
59.362 C
2819.55 ohm

They deviate to a reasonable amount, I don't think that is causing my error.

I think it's my calibration thermister, that is the only one that makes sense that is causing my error.

Edit: Just tested another vernier probe, doesn't seem like that's the problem but might also be the fact that this probe was a stainless steel one which has higher specific heat than my thermistor.

Wawa

As said, compare it to a DS18B20. I would trust that more than a calibrating thermistor.
An even 16 steps/degreeC all the way, and they also come in a waterproof/encapsulated version.
Calibrating that to <0.1 with melting ice (from distilled water), if needed, should be easy.
Just add/subtract the difference, if any, before printing.
Leo..

kendreaditya

As said, compare it to a DS18B20. I would trust that more than a calibrating thermistor.
An even 16 steps/degreeC all the way, and they also come in a waterproof/encapsulated version.
Calibrating that to <0.1 with melting ice (from distilled water), if needed, should be easy.
Just add/subtract the difference, if any, before printing.
Leo..
So use it in place of the vernier probe?

Wawa

Yes.
A semicinductor-based sensor with integrated 12-bit A/D (don't tell them that part) doesn't need a precision resistor or a Steinhart-Hart equation that can influence the end result. You just request the temp in degreeC (or degreesF) from the sensor directly.
Leo..

kendreaditya

Yes.
A semicinductor-based sensor with integrated 12-bit A/D (don't tell them that part) doesn't need a precision resistor or a Steinhart-Hart equation that can influence the end result. You just request the temp in degreeC (or degreesF) from the sensor directly.
Leo..
As much as I would want to do that, I can't. Plus, the sensor cannot come with a waterproof housing :(

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