Patent GB-1016801-A (GB)
Title: Heat detection device with test system
IPC: G08B17/06
Filed: 1962-07-10
Abstract: 1,016,801. Automatic fire alarm systems. J. E. LIMBERG. July 10, 1962 [July 13, 1961], No. 26496/62. Heading G4N. A fire detection system, particularly for an aeroplane, includes a heat sensitive sensor of the type described in Specification 961,143 in which gas is evolved by a substance E, Fig. 3 (e.g. a metallic hydride) contained in a metal tube D, the gas pressure at a predetermined temperature being such as to close a known switch 40 (44, 54) thus completing an electric alarm circuit, a testing circuit being included in the system to continuously heat up and test the operation of the sensor. The tube D is heated for testing by passing a current through it directly or through a ribbon, Fig. 14 (not shown) wrapped round the nickel tube D previously insulated by oxidation, the ribbon being of an alloy of carbon, chromium, cobalt and aluminium which oxidizes on heating to form an insulating film. Operating and testing circuits.-The alarm circuit, Fig. 2, consists of lamps 63, 64 connected to contact 60 of the sensor, a battery 66 and a relay 67 connected to a terminal 70 on tube D. When the temperature has risen to a certain level the switch 40 closes to light the lamps 63, 64 and energize the relay 67 which operates a bell 85. The test circuit consists of a test switch 73 connected between a second terminal 71 on tube D and a second battery 74 connected through an ammeter 75 to a normally closed relay contact 76. When switch 73 is closed, tube D is heated until the alarm circuit is completed to actuate relay 67 which breaks the test circuit at contact 76, the cycle being repeated while switch 73 is kept closed. This causes intermittent flashing of lamps 63, 64 indicating correct performance of the system. If it is desired to indicate an overheat temperature below the operating temperature of the system an ammeter 75 having a long time constant is used so that it may be calibrated to indicate the environment temperatureal. The ammeter has contacts 75a, 75b which close to complete a separate alarm circuit 75c at the appropriate environmental temperature. Additional contacts may be provided on the meter which close to give an alarm if the current becomes very high due to failure of the detector to operate. If several zones are to be monitored a stepping switch is used to connect the test circuit to each detector in turn (Fig. 5, not shown), the stepping switch being arranged to stop or energize a warning circuit at any appropriate point. The relay may be replaced by a valve, transistor or magnetic amplifier (Figs. 8, 9, not shown). A pair of elements may be used, Fig. 10, the switches of which are set to operate at different pressures so that the test cycling condition may be set independently of the alarm circuit, the lamps 63, 64 remaining dark, even though the detecting element is test heated and cooled unless a fire occurs, a separate unit (not shown) indicating correct cycling. Contacts 129, 130 of the elements are connected to a relay 132 and lamps 63, 64 respectively while the common sensor D is connected to a relay contact through an ammeter 141. When test switch 142 is depressed switch 126 closes the circuit to energize relay 132 to operate contact 138 to break the circuit. A further arrangement including two elements requires no auxiliary relay or control device (Fig. 11, not shown) while in the embodiment of Fig. 12, the insulated diaphragm 185 is retained in cavity 184. When testing switch 193 is closed current flows through D and diaphragm 185 moves into contact with 186 completing circuit 186, 187, 188 and causing lamps 63, 64 to light.