GB619525A - Apparatus for measuring and detecting magnetic fields - Google Patents

Abstract

619,525. Electric indicating systems. HINE, A., and HITCHINS, H. L. June 7, 1946, No. 17297. [Class 40 (i)] [Also in Group XXXVI] In apparatus for measuring and detecting magnetic fields, a saturable inductor detector D comprises high-permeability cores a, Fig. 1, having opposed primary windings p coupled to a secondary winding S connected in circuit with a potentiometer R, a choke L, and a transformer T. The primary windings are excited by an A.C. of frequency f and a considerably lower frequency f2 is injected between the centrepoint of transformer T and the tapping of potentiometer R. An external magnetic field threading the core a produces an alternating voltage of frequency 2f1 across the secondary of T, dependent in magnitude and phase on the intensity and direction of the external field, and modulated by f2. After demodulation and amplification a signal is produced at frequency f2, magnitude and phase sensitive to the strength and direction of the external field, which frequency may be applied to a phase-sensitive detector to produce a similarly varying D.C. signal, which is fed back into coil F coupled to the detector' so as to oppose the applied field and stabilise the system, and which may operate an indicator of the external field direction, or control a gyroscope. Modifications of the detector circuit are described (Figs. 1A, 1B, not shown) and a mathematical analysis of the detector action is given. In an application to a compass, Fig. 9, two magnetic detectors D1, D2 are arranged along the axes of a craft to measure the components of the earth's horizontal field, and are excited with A.C. of frequency f 1 by generator E, the outputs being modulated at M by A.C. of frequency f2 from generator O. The signals are amplified, demodulated, and fed to a rectifier R in which they are mixed with the original modulating signal f2. Part of the rectified signal is fed back to the detectors and part operates an indicator X.