Carbon monoxide detection using semiconductors - with temp variation giving long term stability and methane detection

摘要

A method of determining the proportion of >=1 gas constituents in a gas mixture, esp. the CO constituents, utilises metallic oxide semiconductors which change their electrical resistance in the presence of reducing gases. The temperature of the metallic oxide semiconductor is periodically changed between two boundaries values, esp. an upper value 400 degrees and a lower value >-20 degrees C, and esp. at approximately room temp. This arrangement enables the high selective sensitivity to the presence of CO in the low temp. ranges to be utilised for detecting CO at the expense of other reducing gases, while the sensitivity in the higher ranges to CH4 and other hydrocarbons enables this end of the temp. range to be utilised for selectively detecting the presence of these constituents. The use of a periodically fluctuating temp. regenerates the semiconductor so that gases which have diffused into its surface do not modify its long term sensitivity.