GB648367A - Improvements in and relating to electric detector of vapours and the like - Google Patents

Abstract

648,367. Determining physical qualities of materials. BRITISH THOMSON-HOUSTON CO., Ltd. June 14, 1948, No. 15957. Convention date, June 14, 1947. [Class 37] [Also in Group XL (a)] Apparatus for detecting the presence of certain substances in a gas comprises means for bringing the gas into contact with a positively charged heated electrode, whereby positive ions are produced and collected by a negatively-charged electrode, giving a current indicative of the concentration of the substance. Certain substances, e.g. the halogens, require the presence of a sensitizing material to allow the formation of positive ions, which material can be controllably heated independently of the positive electrode. In a " direct action " detector (Fig. 1) the gas to be examined is drawn between two platinum cylinders 8, 9, the latter being heated by a filament 11 which may be supported on an alumina cylinder 12. A positive potential is applied to electrode 9, and the ion current measured by a meter 16, the potential of electrode 9 being sufficiently high to cause the ion current to be saturated. The initial impurities in the alumina cylinder 12 may be used as the sensitizing materials where required, or alternatively, the cylinder may be made of an alkali metal glass. In an " indirect action " detector (Fig. 2), i.e. one essentially requiring a sensitizing material, two platinum filaments 25, 26 are employed, the inner filament 26 being wound on a cylinder of sensitizing, material 27. The current through each filament is separately controllable, and the ion current between them is measured by a meter 43, or by a ballistic galvanometer, if the H.T. is made intermittent by switch 44.