Design and modeling of a linear speed sensor with a flat type structure and air coils

Abstract

This paper presents the design and modeling of a linear eddy current speed sensor with a flat type structure and an air coil configuration. The theory of the eddy current speed sensor is based on utilizing the speed component of the induced currents in a solid moving conductor under stationary or alternating source fields. The stationary part comprises one rectangular excitation coil and two antiserially connected rectangular pick-up coils on the left and right sides of the excitation coil in the direction of the trajectory of the moving part. The moving part is considered firstly as a rectangular conducive ferromagnetic solid iron plate, and secondly as a rectangular aluminum plate. A 3D analytical model using Fourier series is developed to analyze the linear speed sensor in Cartesian coordinates. In addition, the 3D numerical finite element method is used for simulations of the linear speed sensor, and the results are compared with the results for analytical methods. The effects of iron permeability on the speed sensor are calculated for a rectangular ferromagnetic solid iron bar or conductor. The experimental results are presented for a linear speed sensor for a rectangular ferromagnetic solid iron plate and also for a rectangular aluminum plate, at variable speeds. The calculation and the experimental results show that the speed sensor outputs differ completely for solid iron conducive plates and for aluminum conducive plates, due to the different electrical conductivities and magnetic permeabilities.