An absolute vector magnetometer

Abstract

A new method of measuring the absolute direction of the Earth's magnetic field has been developed, comprising a cylinder with a radial hole spinning about its axis on air bearings. The device acts like a single-turn coil and a misalignment between the spin axis and the direction of total field causes currents to flow in the cylinder which are detected by static quadrature coils fixed to the instrument frame. The signals are phase-sensitively rectified and fed back to small Helmholtz coils to cancel the small fields producing the misalignment. When combined with an absolute scalar instrument, the vector magnetometer provides complete and continuous absolute vector information, and could find application as a standard observatory instrument.