GB711874A - Flame detection apparatus - Google Patents

Abstract

711,874. Photo-electric flame detection. FIREYE CORPORATION. Jan. 29, 1952 [Feb. 19, 1951; May 19, 1951], No. 2377/52. Class 40 (3) Fires are detected by a device which responds to a particular range of the wide range of frequencies at which all flames are said to be modulated. Building fire detector system, Fig. 1.-As shown, a number of lead sulphide photo-conductive cells 1, 2, 3 are connected in series with. a potential source by resistors 7 and 9. Change of resistance occurring at between 5 and 25 cycles per second as are produced by a flame are transmitted to the grid of an amplifier valve T1 through a condenser 6 which, with resistor 8, attenuates frequencies below 5 cycles per second. A degenerative feedback circuit comprising condensers 15, 17 connected between the anode and grid of the tube attenuates frequencies over 25 cycles per second. Amplifier T1 is resistancecapacity coupled to a similar selective amplifier T3, the output of which is fed through condenser 28, to a valve T4 normally biased to cut off, thus only positive pulses are amplified producing negative anode pulses which are of constant amplitude because of current saturation in the valve. These negative pulses are differentiated, any positive pulses so produced being short circuited by a valve T5. These negative impulses are then used to charge an integrating condenser 37. The presence of flame sends sufficient pulses through the circuit to cut off valve T6 to the grid of which condenser 37 is connected. A sufficiently negative potential will not be established on the grid unless five such pulses are received in a second. Relay FR then drops out completing the circuit of a fire alarm FA energized through the secondary of a transformer 48. Trouble detecting arrangements.-The system is tested by pulses produced at the rate of one per second by a relaxation oscillator comprising a glow tube T2. These pulses are of sufficient amplitude to pass the frequency discriminative amplifier and reach condenser 37. The resulting increase in potential of the anode of tube T6 is transmitted through a diode T8 to the grid of a valve T9 which is unblocked and energizes an anode trouble relay TR. This relay then disconnects a trouble alarm TA, closes a contact in series with the fire alarm FA and transfers its cathode circuit. The cathode was previously held at positive potential by a contact of relay FR, so that the valve was cut off. The correct arrival of the testing pulses completes the cathode circuit of T9 independently of relay FR, thus preventing operation of the trouble alarm. The anode current of valve T9 passes through the fire alarm FA (without operating it) so that alarm TA is operated and the fire alarm is open circuited. Aircraft fire detection system.-This system is a modification of that described with reference Fig. 1 (V.S). The detectors are of special type comprising a housing in which is both a photoelectric cell and a test lamp and are paralleled in threes to the grid of an amplifying valve. Thus where there are 9 such cells three amplifying valves are fed from a common anode load, the signal developed across the load being amplified in tubes T1, T3 and shaped to produce square negative pulses in tube T4 as described for Fig. 1. The output pulses of the tube are then differentiated and passed through a diode to eliminate negative pulses finally charging a condenser which causes an A.C. fed thyratron to fire if the condenser receives five pulses in a second. A latching condenserbetween the thyratron grid and earth is charged when the thyratron fires and holds the thyratron fired if the component of the flame modulated at from 5 to 25 cycles/ second should decrease momentarily. A quick heating diode initially biases the thyratron grid negatively during the valve warm-up period and the thyratron is then biased by a rectified voltage developed across a potentiometer. The apparatus is tested by means of a switch by which any one of the lamps associated with the cells may be illuminated by means of a supply interrupted at say 10 cycles per second. The method of mounting the detectors in aircraft is shown in the Specification. For a piston energized aircraft the detectors are situated in the engine nacelle while the test switch is mounted on the instrument panel. In a jet aircraft the detectors are situated between the engine shroud and the fuselage. Burner control, Fig. 8.-The system is arranged to operate an alarm if the burner is extinguished. A photo-cell 1 responsive to the flame feeds an amplifier comprising tubes T1, T3 sensitive to frequencies in the range 5 to 25 cycles, as described in the previous two embodiments. The positive potentials appearing across load resistor 27 are short circuited to earth by a diode T20. The negative potentials build up across condenser 138 finally blocking A.C. fed tube T22. The anode of this tube is direct coupled to the grid of a tube T21 which conducts operating a relay and extinguishing a warning lamp.