GB191305467A - Improvements in and relating to Detectors of Combustible Gases. - Google Patents

Abstract

5467. Philip, A., and Steele, L. J. March 4. Explosive and combustible gases, detecting.- Relates to detectors of combustible gases of the kind in which an electrically-heated wire of catalytic material is employed and the change of resistance of the wire in the presence of combustible gas gives an indication on a galvanometer, for example detectors in which active and inactive wires form arms of a wheatstone bridge or are arranged in parallel and each in series with one winding of a differential galvanometer. Means are provided for initially balancing the branches of a circuit including active and inactive wires, for equalizing heat-losses by radiation, and for permitting inspection of the wires. As shown in Fig. 2, active and inactive wires 6, preferably arranged alternately to form a wheatstone bridge, are enclosed in tubes 1, 2, and when heated electrically cause a draught therethrough. The wires are joined by strips 9 of german silver, platinum, platinumsilver alloy, &c. mounted on insulating-blocks 10; the battery or galvanometer is connected to the strips 9 through springs 11 carried by a sleeve 13 which with the springs 11 may be moved by a screw to balance the arms of the bridge. Only one slidable connexion may be used. The strips 9 may be arranged in arcs and the adjustment effected by a rotatable member. The radiation effect may be balanced by the provision of an opening in the tubes adjustable by a sliding sleeve or by piercing a suitable number of holes 17 preferably at the top and bottom of the tube surrounding the inactive wires. The apparatus may be mounted in an outer casing which may be filled with gas to be tested as by a pump. A window 18 may be provided in the tube 1, and a similar window with a removable cap in the outer casing, to enable the active wires to be watched so as to avoid excessive heating. For preliminary tests, a separate piece of catalytic material may be provided, or a series of such pieces in the form of cartridge or other fuses may be provided, each adapted to be put in circuit as required.