An Inductive Angular Displacement Sensor Based on Planar Coil and Contrate Rotor

This paper introduces a noncontact, low-cost, and reliable inductive sensor for angular displacement measurement. It is suitable to work in harsh industrial environments. The sensor has simple structure consisting of three key parts: 1) a ferromagnetic stator, which is a pure plane; 2) a ferromagnetic rotor, which has face slots; and 3) four layers of planar copper coils, including primary and secondary coils. Primary coils are supplied with two orthogonal 4000-Hz ac, and secondary coils output a signal whose phase is proportional to angular displacement. Primary coils are designed with sinusoidal shape, so that magnetic field between the stator and rotor has approximately sinusoidal distribution, and finally linearity between the phase variation of output signal and angular displacement is well helped by this design. The structure and working principles of the sensor are explained in detail. Moreover, a sensor model was simulated to verify the feasibility of the sensor working principles and a sensor prototype was designed for actual experiment. At last actual experiment results are given and analyzed, showing that the sensor prototype has achieved accuracy better than +/- 12 arcsec in the range of 0 degrees-360 degrees, and this kind of sensor may have a better performance by improving the layout of primary coils and front-end signal-process circuit.