Temperature due to resistance calculator?

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Discussion Overview

The discussion revolves around creating a calculator to determine temperature based on resistance readings from a thermistor. Participants explore methods for deriving coefficients for relevant equations and the accuracy of their measurements within a specified temperature range.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the question is more physics-oriented and expresses uncertainty about using exponential methods for calculations.
  • Another participant inquires whether the resistance readings are from a thermistor or other electronics, noting that the answer depends on the specific situation.
  • A participant confirms the use of a thermistor and references the Steinhart–Hart equation for temperature calculations.
  • It is proposed that measuring values at known temperatures and fitting them to the equation is necessary, with a recommendation to use the boiling and freezing points of water for reference.
  • A participant shares several resistance and temperature measurements, indicating they have data to work with.
  • Another participant emphasizes the importance of using a thermistor due to the significant variation in temperature with heat dissipation of resistors.
  • A suggestion is made to use spreadsheet software for curve fitting the provided data, along with a caution about the limited range of the current measurements.
  • Participants discuss the need for additional measurements at the extremes of the intended temperature range to improve accuracy.

Areas of Agreement / Disagreement

Participants generally agree on the need for more measurements and the use of a thermistor, but there is no consensus on the best method for deriving coefficients or the accuracy of the current data.

Contextual Notes

Limitations include the dependency on the accuracy of the resistance readings and the need for additional data points to improve the reliability of the temperature calculations.

ISX
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Think this question is more of a physics than math question. Anyways I am trying to figure out how to make a calculator to figure out what temperature something is at based on the ohm reading I get. I have several readings to go by but I think doing it exponentially is the wrong way to go about it since the readings I calculate are not very accurate based on the quadratic regression method I have been doing.

Wikipedia shows the formula on this page (http://en.wikipedia.org/wiki/Callendar-Van_Dusen_equation) but I don't know how to figure out any of the coefficients or anything.

Thanks for any help I can get!
 
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ISX said:
... I am trying to figure out how to make a calculator to figure out what temperature something is at based on the ohm reading I get...
Do you mean using a thermistor, or just by plugging into any random piece of electronics?
The answer depends sensitively on your situation.
 
Unfortunately I think your best (if not only) bet is to measure some values at known temperatures and fit those to the equation. You have 3 constants, so you need at least 3 measurements, more would be better. The boiling and freezing points of water would be the easiest to do. If you don't have/want-to-use a thermometer, you could use the temperature of boiling and freezing of both pure and salt water for 4 total points.
 
I do have many measurements. Here are a few. kOhms is first number Temp (F) is the second.

73.00 5.0
65.00 6.6
56.00 13.0
39.00 28.0
25.80 43.0
24.57 46.2
18.96 53.7
 
I think you should use a thermistor because the temperature varies greatly with the heat-dissipation of the resistors.
 
It is a thermistor..
 
Hi ISX
ISX said:
I just need help on the coefficient stuff.
Do you have Excel or some other spreadsheet program? Just put the numbers you have for temperature and resistance and have the program do the curve fit to a polynomial for you.

For the values you provided, the chart is rather limited and I wouldn't suggest using it for values outside the tested limits, but attached is what you'd get. I'd suggest getting some more measurements, especially at the limits of your intended range (ie: test in boiling water, 212 F, and at -40 F).

Another alternative is to get an equation from the thermistor manufacturer.
 
Last edited:

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