Noncontact Current Measurement Based on 3-D TMR Sensor Array

This article proposed a noncontact current measurement system for in-wall concealed conductors using a 3-D tunnel magnetoresistive (TMR) sensor array. The system employs a linear strip array of three coaxial, collinear TMR sensors (S₁–S₃) with an optimal spacing of 15 mm, designed to detect magnetic fields in three spatial dimensions without physical contact or wall damage. To address positional deviations, including horizontal displacement (eccentricity up to 3 mm) and angular tilt (up to 30°), a geometric correction algorithm is developed based on Biot-Savart law and sensor output ratios; this algorithm calculates the conductor’s intersection point and direction vector to correct for errors. For crosstalk from adjacent wires, a dual-conductor optimization model is introduced, leveraging the Levenberg-Marquardt method to solve nonlinear equations and minimize interference effects in scenarios with parallel conductors (e.g., spacing from 10 to 50 mm). Implemented with the AK09940A sensor (10nT/LSB resolution, ±1200 $\mu $ T range, and 40–70-nT rms noise in low-noise mode), the system achieves a signal-to-noise ratio (SNR) of 50.7–66.9 dB through hardware calibration and averaging of 100 samples. Experimental validation under complex conditions—including horizontal displacement, tilt, and interfering conductors—demonstrates a relative error of less than 2% for currents of 15–40 A at burial depths of 20–40 mm, confirming high accuracy and robustness for building electrical safety applications.