A Microcontroller-Based Interface Circuit for Three-Wire Connected Resistive Sensors

Abstract

This article proposes and experimentally characterizes a novel microcontroller-based interface circuit to read three-wire connected resistive sensors, which are quite common in industrial applications to measure, for instance, temperature. The circuit relies on measuring, via an embedded digital timer, four discharging times corresponding to four different RC circuits, which include the sensor resistance and the parasitic resistance of the wires. A prototype has been built with a commercial microcontroller measuring resistances that correspond to a Pt100 thermal sensor and with different values of wire resistance. According to the experimental results, the error, with respect to the case with null wire resistances, is lower than 25 mΩ for a 5-m interconnecting cable. In addition, the non-linearity error is lower than 0.02-0.03% full-scale span, regardless of the wire resistances and also of any potential mismatch between them.