Patent GB-627686-A (GB)
Title: Improvements in or relating to electric systems responsive to the rate of change of alternating current signals
IPC: G05D3/14
Filed: 1945-01-22
Abstract: 627,686. Electric follow - up systems. SPERRY GYROSCOPE CO., Inc. Jan. 22, 1945, No. 1708. Convention date, Jan. 22, 1944. [Class 37] [Also in Group XXXVIII] In a rate-taking circuit for use with A.C. operated follow-up systems and the like, a load impedance is alternately connected and disconnected to the alternating signal source, in synchronism with the signal peaks, by mechanical or electronic switching means operated by a constant reference alternating voltage, harmonically related to the signal voltage. A steady direct voltage appears across the load when the signal is uniform, and an alternating voltage proportional to the rate of change when the signal amplitude is changing. In Figs. 5, 6, a gyrocompass has a pick-off device 107 of the type described in Specification 360,428, [Group XXXV], which produces a reversible phase alternating signal dependent on the deviation between the compass card 106 and the followup member 105, the signal operating a twophase follow-up motor 109 in known manner through known amplifying means 117, 124. A rate-taking circuit according to the invention may be switched in to superimpose on the alternating displacement signal applied to amplifier 124 a further alternating signal dependent on the rate and sense of the variations in the displacement signal. The signal derived from the pick-off device is amplified and applied in push-pull manner to electronic switches 150, 160 which each consist of a pair of back-to-back connected vacuum tubes, the switching circuits being completed by resistors 147, 152 and condenser 146. The tubes constituting switch 150 are biassed by condenserresistance networks 154, 156, 153, 155, in series with secondaries 161, 162 of transformer 159 which is fed with A.C. harmonically related to the A.C. signal through a phase shift network 158. The tubes of switch 160 are similarly biassed by networks 163, 165, 164, 166 in series with secondaries 167, 168, and the circuit constants and phasing are arranged so that switch 150 is cut-off except for a short period at the positive peaks of the pick-off signal, while switch 160 is cut-off except for a similar period at the negative signal peaks. Condenser 146 is thus alternately charged through resistors 147, 152 with currents dependent on the instantaneous amplitudes of the positive and negative peaks of the signal voltage, and the voltage developed across the condenser contains an alternating component at the signal frequency, respectively dependent in magnitude and phase on the rate and sense of change of the displacement signal. The rate-signal passes through a low-pass filter 171 and is injected in series with the displacement signal to the input of amplifier 124, the phase shift network 178 being adjustable to ensure that the ratesignal is supplied in appropriate phase to suppress hunting of motor 109. In other forms of the invention (Figs. 1, 3, 4, not shown), a single thermionic switch may be used to supply a rate signal to a dynamometer measuring instrument and battery bias may be supplied to the grids of the switching tubes. Electronic switching means may be replaced by a mechanical switch 'driven by a synchronous motor supplied with a reference A.C. harmonically related to the signal.