On the variance propagation of thermistor-based measurements with a digital temperature controller

Abstract

Thermistor-based measurement systems at constant temperature have been widely used in multiple applications. In this type of hot-wire measurement applications, either analog circuits or digital processors can be used to regulate the thermistor temperature. The sampled-data control is an interesting alternative for temperature regulation because measurement signals are commonly handled by digital processors nowadays. However, the temperature control of Negative Temperature Coefficient (NTC) sensors present a nonlinear behavior in closed-loop operation. Furthermore, measurement variance depends on the temperature of the ambient and the dissipated power, but these relationships are nonlinear. This work proposes an approximated closed-loop propagation model for the output variance of an NTC-based measurement system at constant temperature. The thermistor temperature is regulated with a digital controller. Simulation and experimental results are presented in order to illustrate the benefits of the proposed model.