Development of Modified AC Bridge Network for Accurate Measurement of Passive Parameter of a Temperature Sensor

Abstract

The Resistance Temperature Detector (RTD), acts as a resistive transducer, in which a small resistance changes linearly according to the change of temperature in industry. The inferential technique of temperature measurement by resistance temperature detector needs bridge circuit to measure the temperature in terms of resistance. But the effect of stray capacitances generally produce errors in measurement using bridge network. Wagner-earth technique is very useful to eliminate these errors but this method is suitable for intermittent measurement and not acceptable for direct as well as continuous measurement. In this paper, an AC Wheatstone bridge circuit has been modified by operational amplifiers, so that stray capacitances are assumed to be minimised and with the additional linear potentiometer which provides the variable sensitivity in the bridge measurement. For a constant and selected value of bridge sensitivity potentiometer, the change of resistance with the change of temperature has been observed and found satisfactory with respect to good accuracy, linearity and repeatability. A comparative study of this technique with the laboratory standard instrument has also been reported in this paper.