Voltage divider resistance for high-resolution of the thermistor temperature measurement

When measuring temperature with a voltage divider, and changing the variation of the thermistor resistance from the temperature to the voltage, the divider resistance greatly impacts the resolution of each ADC step. This work presents a method for determining the divider resistance to minimize the resolution’s maximum value in a given temperature range. Since the function of the resolution strongly depends on the derivative of the thermistor resistance, we also investigated the effect on the resolution when the derivative was calculated by forward and backward finite differences and the Stein–Hart calibration equation. The results showed that the resolution’s maximum calculated by the three methods had only a 5% difference, for the four types of commonly used NTC thermistors. Also, we demonstrated that the divider resistance which minimizes the interval resolution’s maximum can be determined by the thermistor resistance and its derivative at each end of the temperature range.

► The divider resistance is optimized for thermistor temperature measurement.
► The resolution’s maximum per ADC step in a temperature interval is minimized.
► The thermistor resistance and derivative only at the interval boundary are related.
► One-degree finite differences provide the bounds to the optimum divider resistance.
► The Stein–Hart calibration equation can be employed for the derivative estimation.