Simple Two-Wire Lead Compensation for Resistive Sensors Using Microcontroller ADCs

This article introduces a simplified two-wire measurement system for accurate resistance measurement of resistive sensors, leveraging the Anderson current loop. The proposed configuration features a precision reference resistor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {ref}}$ </tex-math></inline-formula>) and two diodes (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}_{{1}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}_{{2}}$ </tex-math></inline-formula>), directly interfaced with the analog-to-digital converter (ADC) and output pins of a microcontroller, eliminating the need for external stabilization resistors. Utilizing ratiometric voltage measurements and an adaptive tuning factor, the system effectively compensates for lead-wire resistance and diode mismatches. A prototype implemented with an ATmega2560 microcontroller demonstrates accurate resistance measurements in the range of 60–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$320~\Omega $ </tex-math></inline-formula>, corresponding to a Pt100 sensor, achieving an uncertainty error of less than 0.13% for a lead-wire resistance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.87~\Omega $ </tex-math></inline-formula> and 0.15% for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10.0~\Omega $ </tex-math></inline-formula>. Experimental results confirm the system’s precision and reliability over long lead lengths, offering a cost effective and robust solution for industrial and remote sensing applications requiring accurate temperature measurements.