Patent GB-708345-A (GB)
Title: Failure-warning arrangement for signal-transmission channels in navigational apparatus
IPC: G05D1/02
Filed: 1951-05-11
Abstract: 708,345. Radio navigation testing devices. SPERRY GYROSCOPE CO., Ltd., and MANTEUFFEL G. S. V. VON. May 9, 1952 [May 11, 1951], No. 11179/51. Class 40 (7). [Also in Groups XXXVI and XXXVIII] A device for testing centre-zero control apparatus that includes a transmision channel for transmitting a control signal comprises means for excluding the control signal from the input of the transmission channel and injecting in its place a test signal adapted to provide a known indication in a visual indicating instrument connected to the output of the channel. Fig. 1 shows apparatus for controlling the elevator 13 of an aircraft in response to signals from a control device 1, which may be a pick-off mounted on a gyroscope. The control signals are suppressed carrier modulated alternating voltages, the control device 1 being a pick-off energized from an A.C. source 2 and indicating deviation from a desired pitch angle. The control signals are fed as an input signal to a transmission channel 3 which comprises a device 4 for producing a signal proportional to the rate of change of the input signal, a mixing device 5, an amplifier 6 and a rectifier 26. The output of the transmission channel is a D.C. voltage of reversible polarity and is fed to a Ward-Leonard system comprising a generator 9 rotated at constant speed by a motor. The output of the transmission channel 3 is fed to the field winding of the generator 9, the armature voltage of this generator driving the motor 10. The output of the generator 9 is also fed to a centre-zero indicator 12, which indicates zero if the aircraft is correctly trimmed. The motor 10 rotates a shaft 14 coupled to the elevator 13 through a clutch 25. The shaft 14 also drives a pick-off device 11 energized from the A.C. source 2 and providing an output signal which measures the displacement of the elevator from its mean position. This signal is fed into the mixer 5 so that the displacement of the elevator is made proportional to the sum of the other inputs fed into the mixer 5, viz the signal from the pick-off 1, the output of the rate circuit 4 and the output of an altitude responsive device 16, which may be disconnected by a switch 19. An auxiliary signal is produced by a generator 17 and is fed through the transmission channel 3 to test its operation by means of a relay A when a push-button switch 21 is operated. The signal generator 17 may comprise a transformer connected to the A.C. source 2. When the relay A is operated the input terminal of the channel 3 is changed over at the contacts A3 from the control device 1 to the signal generator 17, while the contacts A1, A2 disconnect the altitude responsive device 16 and pick-off device 11 from the mixer 5 and the contact A4 disconnects the generator 9 from the servomotor 10 so that the only input to the transmission channel 3 is that from the signal generator 17, and the output from the generator 9 operates only the indicator 12. The voltage from the generator 17 is such as to give a half-scale deflection on the indicator 12 when the transmission channel is operating corfor an aircraft in which the vertical pointer 51 rectly. Fig. 2 shows part of a navigation system of a centre-zero indicator 49 is operated in accordance with the sum of component control quantities provided by the roll pick-off of a gyro-vertical 31, a localizer receiver 32 and the pick-off of an azimuth gyroscope 33. The outputs of the pick-offs 31, 33 consist of alternating voltages at 400 c/s, whilst the output of the localizer receiver 32 is a D.C. voltage which is fed to a modulator 34 giving an A.C. output at 400 c/s. These three signals are mixed in a mixing amplifier 37, the output of which is fed to a rectifier 38. This gives a D.C. output dependent in magnitude and polarity on the algebraic sum of the control quantities supplied to the mixing amplifier 37, this output being fed to one of the operating coils of the cross-pointer instrument 49. A source of D.C. voltage 35 is supplied to the transmission channel 34, 37, 38 to test its operation when the relay contacts B1, B2 are changed over, on operation of a relay B by a push-button switch 61. At the same time the other inputs to the mixer 37 are disconnected at the contacts B3, B4.