Patent GB-642650-A (GB)
Title: Apparatus for responding to magnetic fields
IPC: G01R33/04
Filed: 1946-12-02
Abstract: 642,650. Automatic control systems for magnetometers. GULF RESEARCH & DEVELOPMENT CO. Dec. 2, 1946, No. 35607. Convention date, July 21, 1941. [Class 38 (iv)] [Also in Group XXXVI] Alignment; magnetization control.-In a flux valve device responsive to ambient magnetic fields, magnetically separate core members comprising narrow thin strips of high permeability material which is saturable by a low intensity field are cyclically magnetized by separate electrically energized opposed primary windings whose field is superimposed on the ambient field. Each core member successively and abruptly reaches saturation at different phases in the magnetization cycle, the phase difference being variable by changes in the ambient field threading the cores. A resultant sharply pulsed voltage is produced in opposed separate secondary core windings by the phase differences between the saturation points, and is applied to a transducing and indicating device whose response is selective to the sharp voltage pulses and which indicates the ambient field strength. Fig. 1 shows a magnetometer device wherein saturable cores 20, 21 carry balanced opposed primary windings 22, 23 energized in parallel by a sawtooth waveform generator 26, the magnetic field produced in the cores being superimposed on the ambient field, which combines with the primary, field additively in one core and subtractively in the other core so that the waveforms representing changes of net magnetization in the two cores are displaced with respect to each other and there is a small time difference between the incidence of saturation in the two cores. Consequently time displaced voltage pulses are induced in opposed secondary windings 24, 25 and a resultant sharp differential positivegoing voltage pulse dependent on the intensity' of the ambient field is applied to the grid of tube 36 through transformer 33, an adjustable polarizing current from battery 47 being injected into the secondary to balance out a portion of the field. The output of tube 36 is coupled through transformer 39 to apply a positive-going pulse to the grid of tube 37, which is transformer coupled to apply a positive-going pulse to the leaking-grid detector tube 38, having an indicating instrument 35 in its anode circuit, combined with a bucking-out circuit. The diminution from normal of the detector plate current is proportional to the intensity of the ambient field. The coupling transformers are designed to pass high-frequencies while attenuating low-frequencies and the amplifying valves are biassed almost to cut-off. The magnetometer may be energized by a sinusoidal A.C. saturating the cores in opposite senses on alternate half-cycles, or the unidirectional saturating field may be eliminated so that a sawtooth energizing waveform saturates the cores in one sense only with respect to the hysteresis loop zero axis. Fig. 9 shows a modification applied to the steering of a craft, wherein saturable cores 20, 21 are orientable about a vertical axis. The primaries 22, 23 are energized in parallel by a sawtooth oscillation generator 26 , combined with a similar generator 126, the two generators being coupled through a common anode resistance 58 which causes them to discharge alternately. The opposed outputs of secondaries 24, 25 are transformer coupled to an amplifier 36 driving a gas tetrode 138, the anode circuit of which is supplied with voltage pulses from sawtooth generator 126, the phase-shift in the coupling being such that the anode of tube 138 is energized on arrival of a pulse on its grid, and is de-energized between pulses. The output of tube 138 is cathode coupled to a leaky-grid detector 56 having a motor 35 and a known relay device 57 for rudder control connected in its anode circuits. When the cores are at right angles to the earth's field, the total secondary output is zero, while deviations cause development of pulses having polarity dependent on the direction of deviation. Corresponding changes in the anode current of tube 56 operate the relay device and energize a servomotor to restore the alignment of the cores at right angles to the earth's field or to control the rudder of the craft carrying the cores. For the measurement of the total intensity of the earth's field from a craft, the magnetometer cores of the device shown in Fig. 1 may be orientated gyroscopically at the correct inclination to the horizontal, and orientated in the direction of maximum field by the device shown in Fig. 9. In other modifications (Figs. 10, 11, 12, 13, 14, 15, not shown) devices are described for measuring the time rate of change or the space gradient of the ambient field and for automatically regulating the intensity of a unidirectional D.C. excited field in the cores, compensating the effect of the earth's field; and for combining the primary and secondary core windings. Fig. 16 shows a modification applied to the detonation of magnetic mines on the approach of a magnetic craft. Primaries 22, 23 of spaced cores 20, 21 are energized by a cold cathode gas-filled tube 226 operating as a sawtooth generator of slow period. The opposed secondaries are transformer coupled in push-put! to the grids of cold cathode gas-filled tubes 80 81, the cathodes of which are earthed through an electric detonator 83. Permanent magnets 95, 96 adjacent the cores enable the apparatus to be adjusted for minimal response at a given orientation to the earth's field. Space changes in the ambient field on approach of a magnetic body apply unequal pulse voltages to the grids of tubes 80, 81, and the unbalanced pulses of cathode current explode the detonator. Modi. fications of this device (Figs. 17, 18, not shown) are applicable to magnetometry and to the measurement of anomalies in the earth's field for prospecting and the location of buried metals. Pulse unbalance in the secondary core windings may be indicated by the glowing of one of a pair of gas-filled tubes. The invention is stated to be applicable to the detection of submarines.