Patent GB-604907-A (GB)
Title: Improvements in and relating to apparatus sensitive to magnetic fields
IPC: G01R33/04
Filed: 1944-03-13
Abstract: 604,907. Magnetic tests and measurements. PURVES CORPORATION. March 13, 1944, No. 4689. Convention date, Sept. 17, 1942. [Class 37] A flux valve comprises two elongated laterally spaced cores of ferromagnetic material, an exciting winding on each of the cores, and a pick-up winding surrounding both the cores and the exciting windings. As shown in Fig. 3 the flux valve 10 comprises a pair of cores 11, 32 of equal length and rectangular cross-section positioned parallel to and spaced from one another. The cores may be of permalloy or other high permeability material. The core 11 is surrounded throughout its entire length by a uniform exciting winding 15, the core 12 being surrounded by a similar winding 15<1>. The sections of the cores 11, 12 are uniform throughout their lengths so that the same flux density is obtained in all portions of a core at a given instant. The cores 11, 12 are separated by end spaces 16 of non-magnetic material. Alternatively these spacers may be of magnetic material. A pick-up or output winding 17 surrounds the assembly of cores 11, 12 and their exciting windings. A slight balancing adjustment to compensate for inequalities of the two exciting windings may be secured by relatively shifting the cores 11, 12 before the secondary winding 17 is put on. A more efficient balancing adjustment is effected by means of a potentiometer 22 having an adjustable contact 23 for equalizing the excitation of the cores. The windings 15, 15<1> are connected so as to produce magneto-motive forces in opposite directions, the contact 23 being adjusted until there is no component at exciting frequency induced in the coil 17. The output coil 17 is connected to a phase detector or phasesensitive modulator 25 which is biassed by an alternating potential supplied from a source 20 by way of a frequency-doubler 26. A zerocentre D.C. meter 27 is connected to the output of the phase detector 25 to indicate the direction and magnitude of the magnetic field. The flux valve may be mounted on a rotatable support 28 and manually adjusted to give a null or a maximum reading on the meter 27. In a modification the cores 11, 12 are of unequal length, the shorter being shifted with respect to the longer until inductive balance is obtained with respect to the coil 17. In another modification the exciting windings for the two cores' comprise a continuous conductor and means are provided for simultaneously uncoiling portions of the conductor from one core and re-coiling these portions about the other core. Three flux valves 30, 31, 32, Fig. 5, may be equiangularly arranged in a plane to form a pick-up device 35 mounted on a stabilising gyro-vertical 33. This device is connected to a receiver 36 comprising a star-wound stator 37 and a single-phase rotor winding 38 connected to an amplifier 40. The output from this operates a motor 41 to position a device 42 in relation to the direction of the magnetic field actuating the pick-up 35. A report-back connection to the rotor 38 is provided by a shaft 45 geared to the motor shaft. The output of the amplifier 40 may alternately be used to actuate torque-exerting means for processing a directional gyroscope to a position corresponding to the direction of the earth's field. Fig. 10 shows a pair of crossed flux valves 70, 71 and a crossed coil indicator 78 in which the two output coils 93, 94 of the flux valves are switched in rapid alternation to corresponding indicator coils 74, 75, thus rendering the device operative along only one flux valve axis at a time. A permanent magnet 76 is mounted on a vertical spindle for rotation within the coils 74, 75 to a position corresponding to the direction of the field. A vibrator 80 has its exciting coil 81 connected to a D.C. source 83 in series with the exciting windings 85, 86, which are connected in parallel. The coil 81 attracts an armature 88 which engages a contact 89 thereby short circuiting the coil 81. Vibration of the armature 88 is thus caused and a pulsating unidirectional current flows in the windings 85, 86 for saturating the cores 70, 71 and rendering them sensitive to a magnetic field. The output windings 93, 94 have a terminal of each connected to a junction point 95 and thence to a phasesensitive amplifier-modulator 100. The opposite terminals of the windings 93, 94 are connected to vibrator contacts 97, 98. A rocker arm 102 oscillated in correspondence with the armature 88 carries a pair of insulated contact arms 103, 104. The arm 103 alternately engages the contacts 97, 98 and is connected by a lead 106 to the input of the amplifier 100, so that the output windings 93, 94 are alternately connected to the input of the amplifier 100, in synchronism with the pulsations of exciting current. The arm 104, connected by a lead 105 to the output of the amplifier 100, alternately engages contacts 107, 108 connected to the ends of the coils 74, 75 of the indicator 78. The opposite ends of the coils 74, 75 are joined at a common point 109 and thence connected to the output of the amplifier 100. The output of the amplifier 100 is thereby switched alternately to the coils 74, 75, the coil 93 being connected to the amplifier input when the coil 74 is connected to the output and the coils 94, 75 being correspondingly connected. An additional contact arm 110 connected to the arm 88 may be employed in co-operation with a contact 111 to supply interrupted current from the source 83 to render the amplifier 100 sensitive to the phase of the input potential. A frequency-doubler may be included in series with the contact 111. Specifications 599,428 and 611,204 are referred to.