A two-point calibration of negative temperature coefficient thermistors

Thermistors are the most commonly used temperature sensors. Depending on the required accuracy, they are either calibrated at one temperature point (low accuracy) or three points (high accuracy). In many mass produced instruments, a precision three-point calibration provides accuracy far better than practically required, while adding extra cost for the calibration. A two-point calibration method is described. It allows the reduction of the manufacturing cost while assuring calibrating errors of a thermistor less than ±0.03 °C for a temperature range from 0 to 70 °C. The method is based on the use of a simple logarithmic model where the material characteristic beta is not considered a constant but rather modeled as a linear function of temperature.