Patent GB-756637-A (GB)
Abstract: 756,637. Electric control systems. SPERRY CORPORATION. Aug. 13, 1954 [Sept. 18, 1953], No. 23578/54. Class 40(1) [Also in Groups XX and XXXV] By means of manually operated selector switches, a directional gyroscope may be (a) slaved to a magnetic reference system, e.g. a fluxgate compass (b), run free, or (c), connected to an alternative drive for precessing the gyro at a much higher speed that that effected by the slaving system. The system is particularly useful on carrier-borne aircraft where at take-off the fluxgate or other magnetic reference is liable to error. The directional gyro is then precessed at high speed until it reads the known heading, when it is freed and runs as a free directional gyro until after take off when it is slaved to the fluxgate. As shown in Fig. 1, a directional gyro 1 carries on its vertical spindle 4 a horizontal coil 12 in which a fluxgate compass 7 induces an error signal corresponding in magnitude and phase sense to the magnitude and sense of the deviation of the gyro-reference direction from that measured by the fluxgate compass 7. The error signal is amplified and phase detected at 13 and then fed to the control coil 6 of a motor 5 which precesses the gyro slowly about its vertical axis until the gyro is "aligned" with the fluxgate. A centre zero meter 95 connected across the amplifier output indicates the magnitude and sense of the gyro deviation, and, should this reach too large a value, the pilot may open a switch 94, to free the gyro from fluxgate control, and throw a switch 93 to one side or the other, depending on the sense of the gyro deviation. This connects the precessing motor control coil 6 to one or the other secondary of an energized transformer 96 to precess the gyro at high speed until alignment is achieved when fluxgate control may be resumed by appropriate operation of the switches 93, 94. The heading of the craft is indicated by a pointer 20 actuated through synchros 15-18 from the gyrospindle 4. Detailed circuitry, Fig. 2. The error signal induced in the coil 12 is amplified at 22 and phase-detected at 24, where the reference signal is derived from the doublefrequency ripple produced in the power supply rectifier 25 and a phase shifter 26, the demodulated output actuating the triode portions of a tube 27 differentially to carry correspondingly the current flow in the upper and lower control coils 34, 33 of a saturable reactor 35. This results in an output from the reactor through the control winding 6 of the servomotor 5 corresponding in magnitude and phase sense to the error signal, whereby the motor 5 processes the gyro in the corrective sense. A meter 43 responsive to the differential outputs of the tube 27 indicates the magnitude and sense of the error signal and hence of the gyro-deviation. If it is desired to restore alignment of the gyro at greater speed, a handle 50 is operated to throw a switch 49 whereby a relay 41 is energized and through a switch 39-40 de-energizes the motor winding 6 to cut out fluxvalue control of the gyro, when it runs free. A multi-contact switch 53 is then moved to one side or the other, dependent on the sense of misalignment indicated by the meter 43, whereby the appropriate one of the D.C. control windings 33, 34 of the saturable reactor is energized from a D.C. source B and the circuit of motor winding 6 completed so that the precessing motor is driven at high speed in the corrective sense. As the same time the anodes of tube 27 and thus the meter 43 are energized from battery B over further contacts of switch 53 to indicate the magnitude and sense of the misalignment. Modifications. A further switch 92 may be provided, in parallel with the switch 49, and actuated by the undercarriage of the aircraft as it touches down to free the gyro from fluxgate control. Specification 642,093 is referred to.