GB1377748A - Apparatus for measuring a magnetic field - Google Patents

Abstract

1377748 Magnetometers MISHIMA KOSAN CO Ltd 9 Nov 1971 [9 Nov 1970 21 Nov 1970] 52093/71 Heading G1N In a magnetic thin film fluxgate magnetometer, an alternating bias current of a value corresponding to the width of the hysteresis loop of the output of the sensor Fig.4, is applied to the film, in addition to the driving alternating current, so that weak magnetic fields Hex of values less than the width of the hysteresis loop can be detected. The film (5) may be of permalloy and may be applied by electro-deposition or winding to a glass tube (6) surrounding a copper wire (4) to which the driving A.C. is connected. The glass tube may be omitted. The film may be laminated. In Fig.1, the film is surrounded by windings 7, 8, winding 8, the pick-up winding, being either in two oppositely wound halves or at right angles to the driving current. A capacitor 12 is connected across winding 8 to form a resonance circuit. The A.C. bias current is applied to terminals 16 and 17 or 18 and 19. 14 and 15 are high value impedances. Alternatively a drive winding (21) and an A.C. bias and pick-up winding (23) may surround a plate-like film Figs.7a, 7b (not shown). The drive winding (21) or the winding (23) may be reversed half-way. In Fig.10, an A.C. driving current from source 30 is amplified at 31 and fed to the magnetic sensing element 32 and reference phase generator 33. The output of the element is phase-detected at 34, integrated at 35 and fed to an indicator 36 and, as negative feedback, to the element 32. The negative feedback may be sufficient to reverse the field being measured, the system oscillating between two states in which the output of the sensing element has O and # phases. Alternatively, a non- oscillating mode of operation may be employed in which feedback is used merely to cancel the sensed magnetic field.