An Improved Temperature Sensing System for Diesel Engine Applications

Thermistors are used for temperature measurement in the automotive industry because of their low cost, reliability and sensitivity to small changes in temperature. The thermistor resistance is a nonlinear function of the measured temperature. Normally, a bias resistance is used to linearize the thermistor characteristics. Unfortunately, this leads to reduced resolution at the low and high end of the temperature range. In this paper, a novel design scheme is proposed in which comparator-based logic is used to select one of four bias resistors. The resistor selected depends upon the magnitude of the temperature being measured. This approach provides improved resolution (and consequently improves the overall measurement accuracy) while requiring lesser memory and execution time than existing schemes. The proposed approach also improves the ability to diagnose open and short circuits as well as sensor faults.