A current-excitation based circuit for resistive sensors with lead resistance compensation

Abstract

IoT-assisted measurement systems form the backbone of any kind of automation system. Resistive sensors in such systems are indispensable due to the ease with which they can be interfaced and integrated with an IoT-based system. However, in these systems, it is very commonplace to have a considerable distance between the digital processors and the sensor. Corrective measures, such as the 3 Wire or 4 Wire configuration, have been used to cancel out the lead resistance. Such systems are mostly based on DC-excitation signals. However, the DC-excitation-based resistance measurement systems are affected by the non-idealitities of the components, thermoelectric offset and offset voltages. In this paper, a square wave current excitation-based resistance measurement system for remotely connected resistive sensors is presented. To overcome the limitations posed by the large lead resistance the system is equipped with a 3-wire system. The proposed measurement circuit is experimentally tested with discrete resistances. The system can be programmed to work in the low resistance measurement mode exhibiting a dynamic range of 0.5Ω to 56Ω or the wide resistance measurement mode having a range of 10Ω to 148Ω. It has been verified experimentally that the measurement system is insensitive to lead wire resistance for a change of 1Ω to 22Ω. The results show that the circuit can detect variations in resistance as low as 4.75mΩ while maintaining a wide range of sensor resistance measurements with high linearity. The measurement error of sensor resistance using the proposed circuit is calculated to be less than 2% over the entire working range.