Patent GB-628819-A (GB)
Title: Improvements in and relating to remote indicating magnetic compass systems
IPC: G01C19/40
Filed: 1946-07-30
Abstract: 628,819. Compasses. BRITISH THOMSONHOUSTON CO., Ltd. July 30,1946, No. 22705. Convention date, July 30, 1945. [Class 37] [Also in Group XXXVIII] In a remote-indicating compass system of the flux-gate type, deviation of the transmitter is compensated by an adjustable voltage producing device inserted between the transmitter and indicator. As shown, Fig. 1, the transmitter 1 and receiver 2, of known type, each consist of an annular magnetic core 3, 15, e.g. of " Mumetal " (Registered Trade Mark), carrying a saturating winding 4, 16 fed from a singlephase supply 6, and two pairs of coupling coils the coils of each pair 7, 8, 18, 19 being wound at diametrally opposite positions on the core and the two pairs on each core being mounted in quadrature relationship. A . pair of bar magnets .13 rotatable about the pendulum stabilized vertical axis 12 normally in the plane of the core 3 takes up a position according to the horizontal component of the earth's magnetic field and results in the induction of corresponding second harmonic voltages in the coupling coils 7, 8, which, being connected in series with the respective coil pairs 18, 19 produce a resultant diametral magnetic field in the receiver 2 in angular correspondence with the magnets 13. The bar magnets 23 align themselves with this field and rotate a pointer 25 to indicate the compass direction on a stationary card 26. The compensator 27 is similar in construction to the transmitter except that within the core 28 cylindrical bars 33, 34 magnetized diametrally are disposed in quadrature in the plane of the core 28. By means of knobs 37, 38 the magnets 33, 34 are adjustably rotated to produce a resultant diametral magnetic field across the core 28 which by induction produces second harmonic voltages in the coupling coils 31, 32 connected in series with the respective transmitter and receiver coils 7, 18 and 8, 19, which cancel out the effect of the transmitter deviation, produced by the magnetism of the compass-carrying vehicle, on the receiver. The receiver 2 will thus indicate true magnetic north although the transmitter remains uncorrected for deviation. In a modification, Fig. 2 (not shown) the compensator coupling coils 31, 32 are connected in parallel with the corresponding coupling coils of the transmitter and receiver to produce a current compensation effect on the transmitter which then also indicate true north. In this case the compensator should not affect the receiver and this is achieved by suitably choosing the impedance of the receiver so that compensator current flow therein produces a magnetic flux in phase quadrature with the exciting flux. This arrangement may be modified, Figs. 3, 4 (not shown), by providing both series and parallel coupling coils on the compensator to prevent compensator current flow in the receiver. In another arrangement, Fig. 5, the separate coupling coils are dispensed with, the single phase exciting coils 41, 42, 43 being tapped at symmetrical points 6a, 45, 46, &c. to produce, and transmit, the second harmonic voltages. The operation is otherwise identical with that of Fig. 2. Reference has been directed by the Comptroller to Specification 803,448,