Gas detection method

A method for measuring the concentration of a sample gas in an oxygen-containing carrier gas comprising the steps of:

• (a) continuously flowing said oxygen-containing carrier gas which also contains said sample gas whose concentration is to be measured, by way of entry through a first inlet tube into and through a central, solid electrolyte inner detector tube, said first inlet tube being disposed at one end of said central, solid electrolyte inner detector tube, and by way of discharge through a first outlet tube therefrom at the other end thereof, said first outlet tube substantially eliminating back-diffusion of air into said central, solid electrolyte inner detector tube, said central, solid electrolyte inner detector tube comprising an oxide of a tetravalent metal doped with an oxide of an element having a valence less than four, said central solid electrolyte inner detector tube being provided with an internal electrode in contact with the interior of said central, solid electrolyte inner detector tube, said internal electrode being provided with a first, electrically-conductive output lead, and also with an external electrode which is in contact with the exterior of said central, solid electrolyte inner detector tube, said external electrode being provided with a second, electrically-conductive output lead, whereby to bathe a first interface comprising said internal electrode and the interior of said central, solid electrolyte inner detector tube only with said continuously flowing oxygen-containing carrier gas which also contains said sample gas, said interface being maintained at a predetermined temperature;
• (b) continuously flowing a reference gas by way of entry through a second inlet tube into and through an annulus between said central, solid electrolyte inner detector tube and an outer, concentric non-porous tube, said second inlet tube being disposed at one end of said annulus between said central, solid electrolyte inner detector tube and said outer concentric, non-porous tube, and by way of discharge through a second outlet tube from said annulus between said central, solid electrolyte inner detector tube and said outer, concentric non-porous tube at the other end thereof, said second outlet tube substantially eliminating back-diffusion of air into said annulus, whereby to bathe a second interface comprising said external electrode and the exterior of said central, solid electrolyte inner detector tube only with said continuously flowing reference gas, said interface being maintained at the same said predetermined temperature as recited hereinabove in step (a);
• (c) sealing said first inlet tube to, said first outlet tube from said second inlet tube to and said second outlet tube from said central, solid electrolyte inner detector tube and said outer concentric non-porous tube to provide a sealed unit;
• (d) both said oxygen-containing carrier gas which also contains said sample gas, and said reference gas having a low level, impurity concentration of oxygen;
• (e) generating an electrical signal between said electrodes, said electrical signal being directly proportional to the concentration of said sample gas to be determined;
• and
• (f) measuring said electrical signal to determine the concentration of the sample gas as a linear correlation of said electrical signal.