The thermistor resistance can easily be measured, but the temperature is buried inside an exponential. Since all R and T are positive real numbers, we can apply a logarithm ln to both sides of the equation. Doing so allows us to solve for the temperature T,
Alternatively, some references use the negative temperature coefficient (NTC) a to describe the sensitivity of a thermistor,
Typically, the value of a falls between 2% ~ 8%.
With the above equations, the temperature can be directly obtained from the measured resistance. Note that the material constant b may vary slightly with temperature and is usually provided by vendors. One can also use several well known temperature conditions as check points, e.g., ice water at 0 °C (32 °F) and boiling water at 100 °C (212 °F), or use other precalibrated thermometers to calibrate/curvefit the value of b.
However, b may vary considerably across the temperature range of interest. In this case, one should resort to a calibrated curvefit of the RT relationship and neglect the equations presented above. A suitable curve fit is suggested by,
