GB134338A - Detector for Varying Magnetic Field. - Google Patents

Abstract

134,338. Hunt, F. O. Nov. 4, 1918. Magnetic measurements; electro-magnetic current meters.-For detecting the presence and direction of weak varying or alternating magnetic fields and for use in oscillographs and vibration galvanometers, pole-pieces are employed which are magnetized by permanent magnets or electromagnets to a flux-density corresponding to the steepest part of the magnetization curve. In the form shown in Fig. 1, two laminated pole-pieces P are magnetized by an electro-magnet M. Over the gap between the pole-pieces P is adjustably mounted a vibrating reed R of magnetic material. The presence of a varying or alternating magnetic field is indicated by vibration of the reed, its direction being determined by cessation of this vibration when the axis of the pole-pieces is at right-angles to the field. The reed may tilt a mirror or cause a diaphragm to emit a sound- Alternatively, the magnetic changes may be detected by coils C on the pole-pieces connected to a vibration galvanometer or telephone T, the reed acting as an amplifier; or the reed may be omitted and an external amplifier V utilized, in which case the pole-pieces may be replaced by a continuous laminated bar. The reed R may enter the space between the pole-pieces, or may be edge or end on to the pole-tips. In the form shown in Fig. 2, the pole-pieces P are magnetized by permanent magnets M. The reed is replaced by a suspended member R', the period of oscillation of which can be varied for tuning by varying the current in a coil t on a central projection providing magnetic control. When used as a vibration galvanometer, the current to be measured is sent through the coils C. To avoid disturbance by external fields, the pole-pieces P mav be set parallel to one another and polarized in the same direction with the controlling pole-piece between them. When permanent magnets are used for pclarization, the adjustment of magnetic strength may be effected by magnetic shunts. According to the Provisional Specification, the invention may be applied to the detection of the presence and form of hidden magnetic bodies.