Investigation of leakage flux in a capacitive angular displacement sensor used in torque motors by 3D finite element field modelling

Abstract

This paper describes the finite element (FE) investigation of leakage flux in a capacitive angular displacement sensor used in specialised limited-angle torque motors for rotor position sensing. The investigation is carried out by 3D FE modelling and computation of electrostatic field distribution in the complex geometry of the cylindrical sensor. The effects of the axial leakage flux are investigated by comparing the results of 3D and 2D electric field distribution in this small length-to-diameter ratio sensor. Results are presented in terms of 3D potential plots and the effects of leakage flux are assessed by comparing the output characteristics, V= f( θ), of the sensor obtained by modelling and experiment. It has been shown that the axial leakage flux does not have much effect on the magnitude and linearity of this output characteristic which is attributed to the shielding effects of the earthed motor back plate and other geometric features of the sensor.