Patent GB-587817-A (GB)
Title: Improvements in or relating to navigation instruments operating according to the induction principle
IPC: B63B49/00
Filed: 1945-01-18
Abstract: 587,817. Earth inductor compasses. SVENSKA AKTIEBOLAGET GASACCUMULATOR. Jan. 18, 1945, No. 1508. Convention date, Jan. 21, 1944. [Class 37] A number of magnet cores excited by the earth's magnetic field are arranged radially about a rotor and provided with windings in which voltages are generated, the windings being connected to a phase measuring instrument. As shown in Fig. 1 a four-pole rotor 10 rotates between ferro-magnetic cores 11, 12, 13, 14 carrying windings 15, 16, 17, 18, diametrically opposite pairs of which are connected in series with each other to amplifiers 19, 20. The output terminals of the amplifiers 19, 20 are connected to pairs of deflecting plates of a cathode ray tube 21, a line 22 on the screen of which indicates the angle a between the horizontal component Hh of the earth's field and the axis of the coils 11, 13. In order to determine the sense as well as the direction of the field the cores 11, 13 and also the cores 12, 14 may be polarized in oposite directions either by permanent magnets or by D.C. windings as shown in Fig. 2. The windings 15, 16, 17, 18 serve also as polarizing windings and are connected to a battery 23 in series with resistances 24, 25, 26, 27. The windings are also connected to amplifiers 28, 29, 30, 31, the output sides of which are connected through transformers 32, 33, 34, 35 to rectifiers 36, 37, 38, 39. The rectifiers 36, 37 associated with the windings 15, 16 are connected in series to one pair of deflective magnets 41, 42 of a cathode ray tube 40, the other pair of rectifiers 38, 39 being connected .to the deflecting magnets 43, 44. In a modification the transformers 32, 33, 34, 35 are provided with additional secondary windings which are connected to the deflecting windings 41, 42, 43, 44 without the interposition of rectifiers, so that the indication on the screen is in the form of a radial line. Alternatively a periodic switching device may be arranged to put the amplifiers 28, 29, 30, 31 intermittently out of action, causing the spot on the screen to move to and fro between its real position and the centre with sufficient speed to produce a picture of a line. Fig. 4 shows means for automatic steering and for indicating deviation from a set course The output terminals of the rectifiers 36, 37, 38, 39 are connected to diametrically opposite points of rheostats 46, 47 the contact arms 48, 49 of which are fixed to a shaft 50 so that their angular positions are displaced by 90‹. The shaft 50 is rotated by a knob 51 provided with a pointer 52 which moves over a scale 53. The contact arms 48, 49 are connected to a voltmeter 56, for indicating the deviation from the course, and also to the control grids of pentode amplifier valves 57, 58 the cathodes of which are connected together and to a common bias resistance 59 to ensure that both valves obtain the same amplification. The anode circuits of the valves 57, 58 contain resistances 61, 62 and an inductance 63 with a centre tap. Initial adjustment of the resistances 61, 62 is effected by a screw 65. The anodes of the valves 57, 58 are also connected to the grids of amplifier valves 66, 67, in the cathode leads of which are the windings of a balanced relay 68 in series.with bias resistances 69, 70. The relay is shunted by an adjustable controlling resistance 71. A second voltmeter 72 is connected across the relay 68 and indicates the rate of deviation of the course, owing to the time constant of the circuit 61, 62, 63. Any even number of cores 11, 12, 13, 14, greater than four may be used, and a threephase system may be used for producing the required voltages. Three amplifiers may be employed instead of the four amplifiers 28, 29, 30, 31, namely, one for the two voltages from the coils 15, 16 connected in series in the same direction, one for the coils 17, 18 connected in series in the same direction, and one for one or both pairs of coils connected in series in opposing directions, this last voltage being obtained by transforming in order to prevent short-circuiting.