GB934606A - Improvements in or relating to the measurement of magnetic field strength - Google Patents

Abstract

934,606. Magnetic testing apparatus. GENERAL ELECTRIC CO. Ltd. April 13, 1960 [April 22, 1959], No. 13784/59. Class 37. Magnetic field strength or direction is measured by apparatus which includes a measuring coil and a comparison coil, and means for synchronously rotating the coils in the field to be measured and the constant field of a comparison magnet, respectively. A cylindrical body 1, Fig. 1, rests in and can be rotated in saddle-shaped mounts 2a and 2b. The coaxially mounted tube 3 contains the measuring coil 6 and the comparison coil 7 mounted in end sections 3c and 3b of insulating material, with the planes of their windings parallel to the axis of rotation. Tube 3 is rotatable by motor 12, has a middle section 3a of a non-magnetic alloy, and three slip rings 14, 15 and 16. The comparison magnet consists of bar magnets 8 mounted between two annuli 10 (one not shown) of soft iron, and is shielded by Swedish iron 11. In the circuit of Fig. 2, 20, 21 and 22 represent the brushes contacting slip rings 16, 15 and 14 respectively, and block 29 includes an amplifier. The field component at coil 6 perpendicular to the axis of rotation is determined by driving tube 3 with motor 12, rotating body 1 in saddles 2a and 2b to give coil outputs in anti-phase, and adjusting resistor 23 to give zero output from amplifier 29. An angular scale may be provided on body 1 for measuring the direction of the field component, and the effect of stray magnetic fields on coil 7 may be eliminated by providing a reversing switch in the circuit of one of the coils, rotating the body through 180 degrees subsequent to operation of the switch, and averaging the readings obtained.