Abstract: A method is provided for measuring the concentration of a sample gas in an oxygen-containing carrier gas by continuously flowing the oxygen-containing carrier gas which also contains the sample gas whose concentration is to be measured, into and through a central, solid electrolyte inner detector tube, having a particular configuration to eliminate back-diffusion of air thereinto, the inner detector tube having an internal electrode, provided with a first, electrically-conductive output lead, in contact with its interior surface, and an external electrode, provided with a second, electrically-conductive output lead, in contact with its external surface. This bathes a first interface comprising the internal electrode and the interior of the inner detector tube with only the continuously flowing oxygen-containing carrier gas, at a predetermined temperature.

Abstract: The invention is based on the discovery that in a solid electrolyte galvanic sensor, e.g. an yttria-stablized zirconia body, it is not necessary, as has hitherto been believed, to eliminate all impurities to achieve the important performance characteristics of rapid response time, reduced susceptibility to aging, and improved reliability. It has now been found that these improvements can be obtained by reducing only the concentration of iron oxide (and any other variable valence oxides that sometimes occur) in the sample, and that it is unnecessary to lower the concentration of oxides of fixed valence elements, such as silicon, aluminum, magnesium, and the alkali and alkaline earth metals, many of which tend to occur frequently as impurities in ceramic materials. This inventive selective elimination of only the variable valence oxides saves substantial cost in manufacture without loss of the performance advantages mentioned above. Indeed, better mechanical properties are often obtained.