Improvements in or relating to apparatus for indicating the presence of inflammable vapours or gases

摘要

PICT:0682663/III/1 An apparatus for detecting the presence of inflammable vapours or gases in the atmosphere is of the type wherein the gas diffuses into a porous vessel 6 containing an electrically heated filament 5, the vacuum produced in the vessel by combustion of the gas, being utilized to short-circuit, through the medium of a switch 12, 13 actuated by a diaphragm 10, a pilot lamp 1 and thereby illuminate a higher rating warning lamp 2 connected in series with the pilot lamp, when the percentage of inflammable gas reaches a predetermined figure and the apparatus is characterized in that the two lamps are connected to the source of current through a thermally operated switch 7, 8, e.g. a bimetallic strip, positioned within the porous vessel and capable of being maintained in a closed position by the heat from the filament. The filament is connected in parallel with the lamp circuit. Member 14 of the diaphragm actuated switch is a bimetallic strip arranged to bring closer the diaphragm contacts to compensate for fall in battery voltage and deterioration of the filament during use.