GB348612A - Improvements in protective systems - Google Patents

Abstract

348,612. Protective systems controlled by light-sensitive cells. ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Bush House, Aldwych, London.-(Assignees of Breisky, J. V. ; 7505, Rosemary Street, Pittsburg, U.S.A.) Nov. 5, 1929, No. 33658. Convention date, Nov. 6, 1928. Void [Published under Sect. 91 of the Acts]. [Classes 47 (i) and 47 (ii).] In a system wherein a light-sensitive device is employed for indicating or combating abnormal conditions, such as the presence of smoke in a place to be protected, the varying current flowing through a light-sensitive cell in response to changes of light intensity is employed for biasing the grid of a thermionic tube. The output of the tube, which varies in accordance with the current through the cell, is employed for controlling three electromagnetic relays. One of these controls contacts in a work-circuit, whereby protective arrangements, such as fire-extinguishers, are brought into operation when abnormal, e.g. smoke, conditions occur. The other two relays control means for indicating upward or downward fluctuations of the normal working conditions of the circuit. As shown, a mains transformer 14, with two secondaries 17, 18, is employed with a rectifier 19. The secondary 18 is used for heating a light source 47 and the filament 29 of a thermionic tube 28. The grid 31 of the tube is biased from a resistance 23 in the rectifier circuit, and the circuit of the anode 33 includes electromagnets 38, 39, 41 and an indicating instrument 42. A light-sensitive cell 43, which is constantly illuminated by the lamp 47, is inserted in the return lead from the grid 31 to the centre tapping of the secondary 17. In use, the illumination of the cell 43 by the lamp 47 results in a certain current through the cell, a certain bias on the grid 31, and, in consequence, a certain current in the anode circuit, which current holds all the relays inoperative. Should the anode current fall or rise slightly owing to fluctuations in the normal working conditions in the system, the relay 38 or 39 becomes operative to close contacts in the circuit of an alarm bell 60. Should smoke be present in the protected area, the anode current rises sufficiently to energize the relay 41 and close contacts in current leads 51, 52. This results in the operation of an electromagnet 54 which opens the valve 59 of a cylinder 58 of fire-extinguishing gas. As illustrated, the lamp 47 and cell 43 are arranged above a work-table 49 on which smoke conditions may occur. The system may be employed for giving notice of a break in the web in the manufacture of paper.