A Phasemeter for Photoelectric Measurement of Magnetic Fields

Magnetic fields are sensed by means of the Faraday effect. Corresponding electrical signals in phase quadrature are generated. An auxiliary oscillator is used to obtain a phase modulation proportional to the magnetic field to be measured. Demodulation is performed by a phasemeter described in detail. This phasemeter keeps track of multiples of 2π by digital accumulation and performs linear analog interpolation with an accuracy of 2π/1000. The hybrid digital/analog output has an arbitrarily wide measuring range. In addition, a purely analog output is provided combining the count of increments of 2π with the interpolation. The sampling rate of 40 kHz insures fast measurement response. Results of an experimental magnetic field sensing system incorporating the phasemeter as demodulation unit are presented.