Patent GB-845921-A (GB)
Title: Disaster warning system
IPC: G08B27/00
Filed: 1957-05-15
Abstract: 845,921. Disaster warning systems. STEWART, H. R., and RAILSBACK, H. E. May 15, 1957 [May 29, 1956], No. 15491/57. Class 40 (1). A disaster warning system using normal lowfrequency power transmission lines has means for imposing a higher frequency on the lines and means for applying any selected one of a plurality of pulsed or coded signals and a plurality of signalling devices connected to the transmission lines responsive to the coded signals. The higher frequency is to be generated at the substations of the power transmission system and controlled from a central office, e.g. by signals transmitted over the ordinary telephone system. Substations 64, Fig. 1.-The high-frequency generator consists of a three-phase rotary converter 17 supplied from the mains 11 and coupled to the transmission lines 31-33 through a resonant circuit of inductances 22-24 and capacitances 26-28. A switch 51 interposed between the generator and the lines is controlled from the central office by a relay 54 energized over lines 38 and 56, this switch being opened and closed to produce the coded signals required. A transformer 57 applies the higher frequency voltage to lines 38 and 63 from which it is passed over lines (e.g. telephone wires) to the central office. A relay 34 energized over lines 38 and 39 from the central office closes switch 47 to switch on the rotary converter. Control office.-The central office, Fig. 2, has a terminal strip for each substation whose terminals 38, 56, 39 and 63 are connected to those on the strip 12 of the corresponding substation A, B, C &c. A transformer 77 reduces the mains voltage 71, 72 to a value suitable for transmission over the telephone system (e.g. 24 volts). The transformer is connected by switches 110-114, operable to select required ones of the substations A-E and the corresponding terminals 38 and 39 close switches 47 to start the generators 17 in the substations. A motor 78 controlled by switch 76 drives a series of cam contacts 81-90 selected ones of which are connected to lines 56 by switches 91-100. By this means the switch 51 in the substation is controlled to apply to the lines 31-33 a characteristic signal consisting of pulses and gaps. Terminals 38 and 63, energized at the substation from the coded signal output lines 18- 21 through transformer 57, are connected at the central office to lamps 120-124, one for each substation, which accordingly flashes in response to the code signal applied to the line. An automatic device is provided to cause a selected signal to be sent periodically, e.g. every 24 hours. This consists of a timer 132 adapted to close relay switches 136-140 and apply the starting signal to the terminals 38, 39. After a delay a relay or motor 141 closes contacts 142 to cause the selected signal to be applied to terminals 38 and 56 through contacts 81-90. Receiver.-The receivers are to be permanently connected to the power lines and are adapted to respond to the higher frequency signals impressed on the lines to emit an audible warning. The receivers may have a tuned circuit consisting of a coil and a condenser and a stretched wire tuned to the signal frequency and vibrated by the coil. The wire co-operates with a resonant tube adapted to make the audible note. In another form a tuned blade vibrated by the coil is connected to the lid of the alarm housing which acts as a sounding-board. In another form the high-frequency resonant circuit is used to close a relay contact which energizes a buzzer. A red light and another relay coil may be connected in parallel with the buzzer, the relay serving to activate other alarm devices.