GB1117403A - Traffic controller load relay control circuit - Google Patents

Abstract

1,117,403. Road traffic signals. E. W. BLISS CO. 16 Nov., 1965 [12 May, 1965], No. 48573/65. Heading G4Q. [Also in Division H3] A control system for road traffic signals comprises four bi-stable circuits MM1-MM4, Fig. 1, corresponding respectively to main road green and caution and side road green and caution, each adapted when energized to illuminate the corresponding signal, to de-energize the preceding bi-stable circuit, and to trigger an associated monostable circuit TM which, on timing out, energizes the succeeding bi-stable circuit. Each monostable circuit TM may comprise a unijunction transistor relaxation oscillator having an adjustable time constant. Relay circuit.-The signal lamp circuit includes a relay 52, Fig. 2, arranged in series with a silicon controlled rectifier 20, the relay contacts 54 controlling the energization of the signal lamp 22 from an A.C. supply 28, and is characterized in that the relay is energized by a full-wave rectified pulsating voltage derived from the A.C. supply. Consequently the relay contacts can close on either half-cycle of the A.C. supply, and wear due to migration or pitting is reduced compared with the system which uses A.C. across the relay and rectifier 20 and which can only operate on the same halfcycle of the supply.