# Temperature due to resistance calculator?

ISX
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!

zhermes
By:
... 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?

ISX
Yeah just a little thermistor.

Guess it would be this equation then. http://en.wikipedia.org/wiki/Steinhart–Hart_equation

Temperature range of interest would be -40 to 212F. I just need help on the coefficient stuff.

lzkelley
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.

ISX
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

Sakha
I think you should use a thermistor because the temperature varies greatly with the heat-dissipation of the resistors.

ISX
It is a thermistor..