Hello,
I use the thermistor "B57861S0103F045" (https://en.tdk-electronics.tdk.com/inf/50/db/ntc_13/NTC_Mini_sensors_S861.pdf ) to measure the temperature connected via Excitation circuit # 1 - 10 µA Current Source.
To calculate the Steinhart-Hart coefficients, I use a script from the site: https://www.thinksrs.com/downloads/programs/therm%20calc/ntccalibrator/ntccalculator.html.
I substituted the values from the datasheet into the script and got the coefficients A, B, C.
Next I wrote a Lua-script to read the thermistor data, the temperature values are very different from the calculated ones (see attachment). What am I doing wrong?
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I suspect the problem is that you have computed the 3-term coefficients but we use the full 4-term model.
https://daycounter.com/Calculators/Steinhart-Hart-Thermistor-Calculator....
Actually, it looks like the difference is that model uses "R" where our model uses R/Rt. So 2 things:
1. Your C is the ^3 term so should be passed as D. C should be set to 0.
2. Set R25 to 1.
... but that does not seem to work for me either as shown in attached.
Then I just do not understand how to calculate these coefficients on a datasheet. Everywhere it is proposed to simply enter 3 points of temperature and resistance from the datasheet and the coefficients are calculated. Here, for example, on the site:
https://edwardmallon.files.wordpress.com/2017/04/ntc-steinhart_and_hart_calculator.xls
offer to do it too. The result is the same as my coefficients.
As I understand it, when using 4 coefficients it should just slightly increase the calculations exactly as compared to the method using 3 coefficients, but there should not be any fundamental differences in the coefficients.
It does work. I was just missing a 0 when I entered D. See attached.
I made a tab for your part on our thermistor calculator spreadsheet. See that last set of calculations labeled Steinhart-Hart with "R/Rt" with "R" constants.
https://docs.google.com/spreadsheets/d/1hWFXV-46-L376f4q8T55wZmOqX9fUcbb...
Thank you for help. Everything works perfectly!