GB347761A - Wireless apparatus for protection against theft and fire - Google Patents

Abstract

347,761. Fire alarms. CHARDIN, M. A. J., 15, Rue de Berne, Paris. Feb. 4, 1930, No. 3813. Convention date, Feb. 15, 1929. [Class 47 (i).] A wireless transmitting circuit is arranged with conducting surfaces forming part of an oscillating circuit so that the wavelength of the generated waves is varied by the approach of a person or object or by a substantial rise of temperature ; the waves are received by means of a circuit tuned to the normal wavelength and arranged to operate an alarm when this wavelength is varied. The transmitter comprises two valves 1, 2, Fig. 1, connected in parallel to an oscillating circuit comprising an inductance coil 3 and conducting plates 6, 7, so as to generate oscillations. The grids 9, 10 are connected to one end 4 of the inductance 3 through a condenser 11 shunted by a resistance 12 ; this is stated to maintain the energy constant. In order to ensure constancy of wavelength, the anodes 13, 14 are connected to the terminal 5 of the inductance 3 through a condenser 15 having a capacity such that the reactive anode current passing between the terminals 4, 5 is in phase with the oscillations generated in the circuit. High-tension current is fed to the anodes from direct-current mains 19, 20 through an iron-cored inductance 26 and a choking coil 16. A condenser 27 is connected, as shown, between the anode circuit and a point 8 on the inductance 3 so chosen that the best efficiency is obtained. The filaments of the valves 1, 2 are fed in parallel through a resistance 18 so that should one filament fail a lower voltage drop takes place in the resistance and a higher current is taken by the other filament, thus increasing the anode current of this valve. The heating current from the mains 19, 20 is fed to a battery 17 through a series rheostat 22 and an automatic switch 24 which breaks the circuit in the event of failure of the supply. Final adjustment is effected by a shunt resistance 23. The waves sent out by the transmitter are received on an aerial 28, Fig. 2, at a receiving station and, after amplification by valves 31, 36 are supplied to the grid of a relay valve 38 through a condenser 39 shunted by a resistance 40. In the anode circuit of the valve 38 is a milliammeter 41 and a relay 42. On failure of the supply of oscillations to the grid of the valve 38, the grid becomes positively polarized and the anode current increases considerably. The relay 42 is thereby actuated and closes the circuit of an alarm bell 43, sparking at the contacts 44 being quenched by a condenser 45. An automatic switch 52 closes the circuit of an alarm 55 when current from the mains is deficient. The high-tension current for the valves is taken from the mains through a filter formed by an inductance 58 and a condenser 59. Neon tubes may be arranged in parallel with the condensers 59, 27 for adjusting the high-tension supply. The rheostats 22, 49 for adjusting the low-tension supply may be replaced by iron wire resistances in hydrogen.