Patent GB-1169570-A (GB)
Title: Improvements in Remote Supervision Systems and Devices
IPC: G08B26/00
Filed: 1967-05-22
Abstract: 1,169,570. Selective signalling. SOC. D'ETUDES, RECHERCHES & CONSTRUCTIONS ELECTRONIQUES (S.E.R.CE.L.). 22 May, 1967 [21 May, 1966], No. 23759/67. Heading G4H. A system for the centralized indication and identification of remote alarms, the centralized recording of remote measurements and the central control of remote operations is characterized in that the only connections to the central station are an outgoing and an incoming pair of leads. The system has the following modes of operation. (1) Quiescent mode. The central station, Fig. 2, transmits D.C. down its outgoing pair of leads 1, which, at the remote location, passes via a choke 2, series-connected alarm responsive transducers 4, 5, 6, 7, each having its change-over contact 3 connected to its contact 1 in the absence of an alarm, to an oscillator 11 of frequency f 1  which transmits a signal via a transformer 12 and isolating capacitors 43, 46 back to the central station, Fig. 1, along its incoming pair of leads 13, where a filter 58, tuned to the frequency f responds and maintains an alarm indicating lamp 61 off. (2) Alarm detection and identification mode. If an alarm responsive transducer 4, 5, 6, 7, Fig. 2, detects an alarm its change-over contact 3 changes from 1 to 2 and the series path for the D.C. to the oscillator 11 is broken. Frequency f is therefore not received by the central station and the alarm indicator 61 is actuated. The particular one of the alarm responsive transducers responsible for the alarm indication is then identified under the control of a programme unit 68, Fig. 2, which causes signals of frequencies f 1 , f 2 , f 3 , f 4  from oscillators 50, 51, 52, 53 respectively, to be transmitted sequentially, by a scanner 62, via an amplifier 69 and a filter 54, to the remote station where LC filters 18, 19; 20, 21; 22, 23; and 24, 25 sequentially respond, and via rectifiers 26, 27, 28, 29, sequentially pulse the alarm transducers 4, 5, 6, 7 and that one responsible for the alarm passes the pulse via a threshold discriminator to an oscillator 16 of frequency f<SP>1</SP>. The time of reception of a pulse of frequency f<SP>1</SP> by the central station therefore indicates the identity of the actuated alarm transducer and, as a result, a corresponding lamp 64, 65, 66, 67 is energized by a scanner 63 driven in synchronism with the scanner 62, via a filter 60 tuned to f<SP>1</SP>. (3) Remote indication of measurements mode. By applying a signal of frequency f 1 , f 2 , f 3  or f 4  to the line 1, the programme unit 68 can select one of four measuring units having actuating relays 30, 31, 32, 33. These relays are slow to respond and will not respond to the alarm identifying pulses of the same frequencies because they are too short. The selected measuring instrument, only one, 34, being shown, then transmits its measurement with D.C. signals to the central station where it is extracted from the normally received signal of frequency f 1  by a choke 57 and recorder 70. Once a measurement is complete the recorder 70 can signal 71 the programme unit 68 to continue. (4) Remote control mode. By depressing one of four keys 73, 74, 75, 76 a selected one of frequencies f 1 , f 2 , f 3  and f 4  can be transmitted via associated amplifiers 77, 78, 79, 80 to the remote station. The measuring units respond as before, but their replies are ignored, but because signals of large amplitude are transmitted four control relays 37, 38, 39, 40 respond. Each depression of a key 73-76 is arranged to reverse the state of the device 41, 44 being controlled.