NTC Thermistor Performance and Linearization of its Temperature-Resistance Characteristics Using Electronic Circuit

This paper critically discusses the performance of an NTC thermistor sensor in the temperature range 20 oC to 85 oC and provides a technique for linearization of the temperature sensed by the thermistor. The linearization was achieved by utilizing Wheatstone bridge electronic circuitry which responds to the thermistor and produces an output which is an exponential function of the temperature sensed by the thermistor sensor. A further simple and low-cost electronic circuitry responds to such output and converts the resistance measurement to provide a signal which represents the temperature. Moreover, the Wheatstone bridge signal conditioning circuitry was designed to have 0 – 100 mV output voltage within the considered temperature range. The physical characteristics of the thermistor (constant A and b ) were found to be 4.0015 x 10-5 ± 0.2956 x 10-5 Ω and 3514.8 ± 11.6 K respectively. The result also shows that the percentage nonlinearity was as low as 1.7 and a sensitivity value of 1.5661 mV/K was found for the thermistor, but the resolution of this thermistor sensor is 2 oC. However, the percentage of nonlinearity obtained was in agreement with the theoretical percentage nonlinearity.