Simplified Three-Wire and Four-Wire Interface for Resistive Sensor Measurement Using Microcontroller ADCs

This article presents a simplified three-wire and four-wire measurement method for accurately determining the resistance of sensors, such as resistance temperature detectors (RTDs), using an Anderson current loop configuration. The proposed system employs a resistance-to-voltage (R-to-V) conversion approach, ensuring high accuracy and simplicity while eliminating the need for additional components, such as capacitors, op-amps, or complex timing circuits commonly found in resistance-to-time (R-to-T) conversion techniques. In addition, a tuning technique is incorporated to compensate for analog-to-digital converter (ADC) errors, reference resistance deviations, and lead-wire mismatches, thereby improving measurement precision. This tuning technique requires an initial calibration to determine optimal correction factors, tailored to specific hardware and wiring conditions. A prototype was developed using a commercial ATmega2560 microcontroller with 10-bit ADCs to measure resistances ranging from 50 to $317~\Omega $ , corresponding to a Pt100 thermal sensor, under varying lead-wire resistances. Experimental results, incorporating tuning factor calibration, demonstrate that the proposed technique achieves a relative uncertainty error below 0.1% for both three-wire and four-wire configurations, ensuring accurate and reliable measurements even in the presence of lead-wire variations.