Gas analyzing devices

In a gas analyser comprising a heated catalytic analysing element and a similar heated catalytic compensating element arranged in a balanceable electric network, both elements are situated in a housing, the temperature of which is maintained constant, and are exposed to the cooling action of the gas to be analysed, and means are provided to limit gas flow to the compensating element so that catalytic combustion thereon is substantially prevented. In estimating combustible constituents, such as carbon monoxide, hydrogen, or methane, the gas is mixed with air, and to estimate oxygen the gas is mixed with hydrogen. Catalytic combustion on the analysing element causes a rise in temperature and a change in electrical resistance which is measured by the electric network. As shown, air or hydrogen enters at a constant rate through orifice 9 and mixes with the gas entering through a similar orifice; regulating valves as described in U.S. Specification 2,438,973 are used to supply the gases at a constant pressure and constant rate. The mixture passes through cell 10 and then via line 50 to cell 11. Shield 34 surrounding an analysing platinum filament is provided with a metallic mesh screen through which the gas mixture diffuses, and shield 35 surrounding the compensating platinum filament with a small aperture so as to limit diffusion. The housing containing the cells 10, 11 is maintained at an elevated temperature by a thermostatically - controlled heater. The filaments are connected through terminals 12, 13, 14, 15 in a Wheatstone bridge network.