Patent GB-980630-A (GB)
Abstract: 980,630. Gyroscopic apparatus. GENERAL PRECISION Inc. Dec. 18, 1962 [Jan. 23, 1962], No. 47807/62. Heading G1C. [Also in Division G4] In an inertial navigation system the output from an oscillator 11, Fig. 1, is amplified at 13, passed through a half wave rectifier 15 and applied to a gate 17 and inverter gate 19, so that when a signal from inertial instrument 23 indicates that torque should be applied by torquer 20 in one direction, polarity control circuit 21, acting on the polarity of the signal from instrument 23 enables gate 17 so that a train of constant amplitude pulses is applied to torquer 20 and when the polarity of signal from instrument 23 indicates that torque should be applied in the opposite direction, circuit 21 enables inverter gate 19 so that a train of pulses of opposite polarity is applied to torquer 20, the arrangement being such that when gate 17 is enabled, gate 19 is disenabled and vice versa. The polarity control circuit 21 senses only the polarity of the output signal from instrument 23 and selects the appropriate gate 17 or 19 which will remain enabled until the torquer 20 has acted so long as to cause instrument 23 to reverse the polarity of the signal applied to circuit 21. To ensure that the pulses have equal impulse content, the pulses after application to torquer 20 are applied to a supervisory circuit 27 which controls the gain of amplifier 13. The circuit 27, Fig. 3, comprises a bridge circuit 61 in which one arm 75 is formed from a temperature-dependent resistor enclosed in a thermally controlled chamber so that its ambient temperature is constant (see Division G4) so that the resistance of arm 75 depends on the square of the current passing through it. The arrangement is such that if the pulse is of desired value, no output occurs between lines 74, 76, but if it is not, an output is applied to demodulator 83 of magnitude corresponding to the error in pulse value and of polarity depending on whether it is greater than or less than the desired value and also whether the pulse originated from gate 17 or 19. To allow for the variation in gate of origin, the input pulses are also applied through amplifier 89 to demodulator 83 so that the gain control signal in line 91 applied to amplifier 13 is positive when the impulse content of the pulses is too large and negative when it is too low regardless of which gate they originally came from. Also the pulses from gate 17 and inverter gate 19 are changed over periodically by polarity reverser 29 at a frequency which is a submultiple of that of oscillator 11, the polarity of torquer 20 being similarly changed, so that the output pulses from each gate will take turns in causing torquing in each direction and the effects of any inequality will be cancelled out. In a modification, Fig. 5, instead of this reversal a frequency divider 113 periodically enables, at a frequency which is a sub-multiple of that of oscillator 11, both gates 17, 19, simultaneously. Thus if the positive and negative pulses from gates 17, 19, respectively are of equal value they cancel out across resistor 115, but if not, pulses are produced which are applied to a gate 117, enabled by frequency divider 113 only when it enables gates 17 and 19. Pulses passing through gate 117 are integrated at 119 and used to control the gain of an amplifier 111 positioned before gate 17.