GB587934A - Improvements in gas analyzers - Google Patents

Abstract

<PICT:0587934/III/1> In gas analysis apparatus of the kind wherein combustion of a constituent of the gas with an added gaseous reagent is effected by a heated catalyst connected in a Wheatstone bridge, a switch is provided for changing the sensitivity of the galvanometer to suit gases of various compositions and simultaneously for altering the proportion of reagent gas added. The illustrated apparatus has two combustion cells 13, 95 determining respectively the oxygen and the combustible content of a furnace or exhaust gas. The catalytic filaments 22, 96 of the cells are connected respectively in Wheatstone bridges 36, 35 which are connected in series with one another and supplied with current from rectifier 32. Also included in the circuit is electrolytic cell 15 supplying hydrogen as a reagent to cell 13, while gas to be tested is supplied by pump 9. When testing gases of low oxygen content the multiple switch 42 is in the position shown, connecting the galvanometer 41 in series with calibrating resistance 75. A resistance 76 is connected in parallel with the cell 15, reducing its output. For gases of higher oxygen content switch 42 is turned to the left, recalibrating the galvanometer by substituting resistance 79 for 75, and increasing the hydrogen supply by cutting out resistance 76. Also the rotation of cam 45 drops a perforated shield 25 over the catalyst 22 restricting the access of gas to it. The third position of switch 42 connects the galvanometer to a thermo-couple 82 for measuring the temperature of the gas to be tested in conduit 1. Cell 95 for estimating combustible content is supplied by pump 87 with a mixture of air p drawn through passage 91 and gas drawn from pump 9. The ratio can be changed by turning valve 86 connected to switch 101 which places one or other of the calibrating resistances 116, 119 in series with the galvanometer 100 of Wheatstone bridge 35.