GB653703A - Improvements in or relating to electrical phase or frequency discriminators - Google Patents

Abstract

653,703. Phase difference and frequency measurements. GENERAL ELECTRIC CO., Ltd., and BRYDEN, J. E. July 27, 1948, No. 20078. [Class 37] [Also in Group XXXVIII] In a phase or frequency discriminator two direct voltages dependent in relative magnitude on relative phase, relative frequency or absolute frequency of an A.C. source are successively and repeatedly switched to the input of an amplifier the output of which is successively and repeatedly switched, in synchronism with the input, to a pair of electrical devices giving an indication or effecting a control. In a correspondence control system a transmitter 17 and a receiver 22 are phase-shift potentiometers. e.g. of the type described in Specification 632,007, [Group XXXV], supplied from a sixphase source 20 which may be derived from a single-phase source as described in Specification 642,855, [Group XXXV]. The output of the transmitter, phase-shifted by 90 degrees in a network 23 including a valve buffer stage, and the output of the receiver are applied to a circuit including a centre-tapped transformer 2 and rectifiers 4 developing across resistances 5 two direct voltages which are equal when transmitter and receiver outputs are in phase but differ in magnitude in one sense or the other according to the sense of phase deviation. A contact 8 of a vibrator (not shown), operating at 60 cycles per second, applies the voltages successively and repeatedly to a two-valve A.C. amplifier 10, the output of which is applied to a triode valve 13 energizing relays A and B. The relays are successively and repeatedly shortcircuited by a contact 14 of the vibrator operating in synchronism with contact 8 so that each of the voltages across resistances 5 controls the operation of a different one of the relays. When the voltages are equal neither relay operates but when one or other voltage is the larger upon phase deviation the corresponding relay operates and remains operated to close its contact A1 or B1 and operate a reversible electric servomotor 16 in the appropriate direction to bring the receiver into coincidence with the transmitter. It may be so arranged that when the voltages are equal both relays are operated. To reduce hunting a slow-to-operate relay may be included in circuit with relays A and B to reduce, in its inoperative position, the speed of the servomotor so that the latter only operates at normal speed when the deviation is above a predetermined value for a predetermined period. Lamps may indicate presence or absence of correspondence and the sense of deviation.