An Inductive Sensor System for Linear and Angular Displacement Measurement With Negligible Cross-Sensitivity

This article presents a novel inductive sensor system that can simultaneously measure linear and angular displacements. The proposed sensor system aims to mitigate the drawbacks of existing linear and angular displacement sensors, specifically their interdependence on the measurands and sensitivity to harsh environments. The proposed sensor system comprises two main components, the sensor and the interfacing circuit. The sensor has a fixed part and a moving part. The fixed part includes two solenoidal inductor coils and two pairs of planar square-shaped inductor coils wrapped over a bobbin. The moving part, referred to as the shaft, can rotate around its axis and can move transversely along its axis. A thin ferromagnetic core is affixed to the shaft. The axial movement of the shaft alters the inductance of the solenoidal coils, while the rotational movement affects the inductance of the planar coils. The sensor design ensures that both measurements are independent of each other. The interfacing circuit measures the variations in inductance caused by the axial and rotational movements of the shaft. A detailed error analysis has been performed to quantify the potential errors from the sensor and the interfacing circuit. A prototype of the proposed sensor system, capable of measuring 360° for angular displacement and ±20 mm for linear displacement, was built and tested in the laboratory. The measurement results indicate that the worst case linearity error is less than 0.75% for linear and angular displacement with a resolution of $47~\mu $ m for linear displacement and 0.169° for angular displacement. The sensor system exhibits negligible cross-sensitivity between measurements, emphasizing its suitability for various practical applications.