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

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 $\text{m}\Omega $ for a 5-m interconnecting cable. In addition, the non-linearity error (NLE) is lower than 0.02%-0.03% full-scale span (FSS), regardless of the wire resistances and also of any potential mismatch between them.

Automated summary

This article introduces a microcontroller-based interface circuit for reading three-wire connected resistive sensors commonly used in industrial applications. The circuit measures the discharging times of four different RC circuits, including the sensor resistance and wire parasitic resistance. Experimental results show that the circuit has low error and non-linearity error under specific conditions.