GB899085A - Improvements in or relating to electrical phase sensing circuits - Google Patents

Abstract

899,085. Phase indication. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. March 9, 1960 [March 12, 1959], No. 8638/59. Class 37. Apparatus for determining the relative phase senses of alternating currents in two distinct circuits fed from a common generator comprises a relay fed from one circuit over a transistor device controlled by the other circuit so as to operate only if the currents in the circuits are cophased and to be inoperative if they are antiphased. In a known carrier current signalling system wherein plural repeater stations spaced along a line receive an operating power supply over the go and return signalling conductors which carry voltages which are antiphased about earth, the direction of supply is determined at each repeater station by energizing transformer T1 in series with the supply current to excite the emitter-base circuit of transistor TR1 in shunt with opposed squaring and clipping rectifiers MR1, MR2. Shunt resistor R1 and series register R2 reduce the effects of phase variations with load. The primary of transformer T2 is centre-tapped to earth and energized across the go and return conductors to supply the repeater power, and also its secondary excites the collector-emitter circuit of the transistor in series with half-wave rectifier MR3 and capacitance shunted along relay RA, which operates on conduction of the transistor due to coincidence of the negative-going collector pulses with the negative excursions of the square wave applied to the base to illuminate gas discharge lamp NT2 over contacts RA1, RA2 when the load voltage and current are in phase; and remains inoperative to illuminate lamp NT1 when the load voltage and current are in antiphase due to reversal of the direction of supply. The transistor may be replaced by a bridge rectifier with one diagonal connected across the secondary of T and the other connected in series with the relay and half-wave rectifier to the secondary of T2.