Combined Variable Reluctance-Hall Effect Displacement Sensor

Abstract

A new noncontact displacement sensor employing a combination of variable reluctance technique and Hall effect sensing is designed and developed. The magnetic part of the sensor consists of a sensor head that moves over two identical trapezoidal elements. It is also possible to fix the sensor head and move the trapezoidal parts over it. A permanent magnet (PM) provides magnetic excitation and a couple of Hall sensors sense the fluxes in the magnetic circuit. The direct digital output of the sensor, obtained with a signal conditioning circuit, is unaffected by variations in the strength of the PM as well as variations in the permeability of the magnetic parts. Since, the digital output is insensitive to variations in the actual value of the strength of the PM, any change in the magnetic strength of the magnet (either due to decay or misalignment) will not affect the performance of the proposed displacement sensor. Error analysis presented herein establishes the ground rules to be followed while designing the sensor. Results from simulation and that obtained from a prototype sensor built and tested establish the practicality of the proffered sensor.