A Robust Planar-Coil Variable Reluctance-Based Angle Sensor System With PWM Output

This article presents a novel planar coil-based sensor system for full-circle (0${}^{\boldsymbol{\circ}}$–360${}^{\boldsymbol{\circ}}$) angle measurement using the variable reluctance principle. The system generates a pulse-width modulation (PWM) output, where the on-time is directly proportional to the angle of rotation. It consists of a sensor and an interfacing circuit. The sensor incorporates two pairs of planar inductor coils wrapped around the shaft, with a thin ferromagnetic material attached to a movable shaft inside the bobbin. As the shaft rotates, the inductance of each coil changes, enabling precise angle measurement. Unlike conventional planar coil-based angle sensors, the proposed system offers a linear output, overcoming nonlinearity issues. Additionally, it is immune to misalignment of the shaft and variations in the permeability of the ferromagnetic strip, addressing common challenges in angle sensing. The quasi-digital output eliminates the need for microcontrollers, analog to digital converters (ADCs), or virtual instruments, simplifying system integration. The sensor ensures high-speed conversion with exceptional accuracy, making it ideal for industrial applications. A prototype was developed and tested in the laboratory, achieving excellent linearity (0.28%), high resolution (0.0124${}^{\boldsymbol{\circ}}$), and a low conversion time of 20$\boldsymbol{\mu}$s. Its compact, robust design and superior performance make it highly suitable for industrial and automotive applications.