GB1341372A - Smoke detector - Google Patents

Abstract

1341372 Ionization chambers BEVAKNINGS AB SECURITAS 20 Oct 1972 [20 Oct 1971] 48315/72 Heading H1D In a smoke detector formed by a first ionization chamber which contains a source of ionizing radiation, is located within a housing, and is separated from a second ionization chamber, in communication with the ambient atmosphere, by a common wall transparent to the radiation emitted by the source, the second chamber is defined by an apertured cover which is removably secured to the housing and which is adapted to receive the wall, whereby the wall, when contaminated, is removable with the cover from the housing, to permit replacement by clean parts. As shown, the housing 1 contains an electrode 2 and a flange for the receipt of an insert 6 supporting an aluminium tube 8 containing a radioactive isotope, e.g. krypton 85 or argon 39. The wall 9 is in the form of a membrane, e.g. aluminium foil, which constitutes a common electrode for the two chambers, and which may be secured by adhesive to a holder 12 which is itself secured to an apertured cover 16 forming the wall and second electrode of the second chamber. The cover 6 may be of metal or metallized plastics. The gaseous isotope container, instead of tube 8, may be formed the membrane 9 together with a second, smaller membrane (19, Fig. 8, not shown) sealed thereto.