GB1295503A - - Google Patents

Abstract

1295503 Electric selective signalling COMPAGNIE DES COMPTEURS 16 June 1970 [16 June 1969] 29136/70 Heading G4H [Also in Division H3] In a system of signalling over electrical power lines using pulses of say audio frequency, one or more command pulses are preceded by a start pulse, the interval between the start pulse and the or each command pulse conveying the information. The receiver consists of a number of semi-conductor gates which after the receipt of a start pulse open in succession for periods in which command pulses can be expected. The passage of a command pulse through a gate identifies the command. In the receiver shown in Fig. 2 a mechanical or electrical frequency-sensitive-device 11 closes contacts 12A, 12B in response to each audio frequency pulse on power lines 10, 10<SP>1</SP>. The start pulse causes discharge of a timing circuit 20, and if the pulse lasts for 1.5 secs. in a valid start pulse, the gate potential of uni-junction transistor T 1 , becomes low enough for the transistor to conduct and operate relay 21, whose contact 21 applies anode potential to T 1 and T 2 . Timing circuit 20 2 discharges 3 sees. after receipt of the start pulse to trigger T 2 and conduct transistor TR 2 . If a command pulse now arrives, closure of contacts 12B energizes relay winding 22A to close contacts 22C. 2.5 sees. after triggering of T 2 , T 3 triggers by timing circuit 20 3 to conduct transistor TR 3 and block TR 2 . If a command pulse now arrives the release winding 22B is energized to open contacts 22C. T 3 and T 4 trigger at successive 2.5 sec. intervals and operate on relay 23. The triggering of T 6 2À5 sees. after T 5 resets the receiver by releasing relay 21.