A demodulation inductive proximity sensor with suppression of background magnetic flux density

Abstract

A novel inductive proximity sensor system is accomplished in this paper. Primarily this system uses a modulated magnetic field generator (modulation of current in a coil) and a lock-in receiver which demodulates the magnetic flux density by using a Hall effect device. In contrast to published sensors this approach increases the signal-to-noise ratio (SNR) by a demodulation and a subsequent integration process which is implemented in the lock-in receiver at an isochronous suppression of DC or AC modulated background magnetic flux density. The performance is predicted by simulation and validated by a demonstrator. It is shown that the demodulation inductive proximity sensor works in a hostile environment in which the amplitude of a background magnetic flux density has a similar (or higher) amplitude compared to the active modulated flux density.