GB1383777A - Security system - Google Patents

Abstract

1383777 Security system OAK ELECTRO/ NETICS CORP 24 May 1972 [24 May 1971] 24518/72 Heading G4H In a security system wherein a central station 10, Fig. 1 (not shown), scans local stations (12, 14, 16, 18), series-connected thereto by a transmission loop, by sequentially transmitting their addresses, a relay 24, Fig. 2, in the loop at each local station is allowed to open unless the station address is detected during the scan so that faults in the loop may be located and isolated. Each station (12-18) contains sensors 66 (fire, burglary, water temperature &c.) each of which transmits its reading via a processor 64 to a memory 58. The scanning signals comprise signals of the form 52 (double-length start bit), 54, 79, Fig. 3; when a station address is detected by an address read/decoder 46, 56, memory 58 is allowed to output the sensor data in binary form to an encoder 70 from which it is fed to the transmission loop as a reply signal 78, Fig. 3. An earthing fault between, e.g. (14) and (16) is located when (scanning in one direction around the loop) station (14) fails to detect its address (since its receiver is too weak), thus opening its relay, and when (scanning in the other direction) station (16) similarly opens its relay: stations (14) and (16) are then commanded to hold their relays open (thus isolating the earthing fault) and stations (12), (14) and (16), (18) are scanned alternately until the fault is repaired. Similarly, in the case of an open-circuit fault between (14) and (16), first (12) and.(14) will close their relays, but (16) and (18) will not, and then viceversa: the fault is then isolated and the two arms of the loop scanned alternately as before.