GB698358A - Improvements in fire and other alarm systems - Google Patents

Abstract

698,358. Fire alarm systems. C-O-TWO FIRE EQUIPMENT CO. April 10, 1951 [June 17, 1950]. No. 8327/51. Class 118 (i). [Also in Group XXXVI]. In an electric fire or other alarm system in which a decrease of the current from below a normal level operates a fault alarm, and an increase of the current operates the alarm signal, the detector unit is mounted on a base having terminals which co-operate with contacts in a mounting bracket, so that removal or displacement of the detector unit will operate the fault alarm. Fig. 1 shows an alarm system in which a plurality of detector units are mounted in holders 16. The base connections of the detector unit are such that when inserted in the holder, terminals 45 and 46 are shorted and if rendered operative by the conditions to be detected, terminals 47 and 48 are effectively connected together. When the detectors are in position, a normal current from source 12 flows through relay 15, resistance 104, through the shorted connections in the detector, to earth. This normal current through relay 15 is sufficient to maintain its movable contacts in the non-operative intermediate position. Should the current rise, due to a detector operating and effectively shunting out resistance 104, contacts 39 and 91 are operated, which respectively energize zone indicator lamps 87 and operate alarm relay 95 to operate alarms at a central station or initiate discharge of a fire extinguishing system. Should the current fall, owing to failure of the supply, removal of a detector unit or other circuit interruption, contacts 38 and 97 are operated which respectively operate zone indicator lamps 87 and fault buzzer 100. The detectors and relay 15 and zone indicator 87 shown are associated with a particular locality, and other zones may similarly be protected by providing additional apparatus of a similar type connected to lead wires 105. Fig. 2 shows a suitable detector unit of ionization type, in which the electrical resistance of a standard body of air in chamber 55 is compared with that of air flowing into a test chamber 56. A small hole 57 is provided to equalize pressure in chamber 55, while a large hole 59 in chamber 56 allows air circulation. Each chamber is subjected to the action of radioactive material 66. Electrodes 70 and 71 are positioned in the chambers, and connected together and to the control electrode of a cold cathode tube 74. If ionized particles are present in the air being tested, due to either flame or smoke the potential of the control electrode is changed causing the cold cathode tube to conduct and so operate the alarm relay 15.