Vehicle exhaust gas analysis system with gas blockage interlock

Claim 1

An engine exhaust gas analysis system for measuring the amount of a selected contaminant contained within a sample of engine exhaust gas comprising: a gas sample cell adapted to contain a gas; a reference cell containing a reference gas; means including a gas transport system for filling said sample cell with a sample of exhaust gas; sampling means associated with said cells for producing electrical signals related to the concentration of the selected contaminant within the sample of gas; pressure means connected to said gas transport system and responsive to the pressure of gas therein to generate a blockage signal alternatively indicative of whether or not said gas pressure is in excess of a preselected pressure below which blockage of said gas transport is to be presumed; and a data analysis and control system responsive to said sampling means and to said pressure means, for receiving said electrical signals and calculating therefrom the concentration of the selected gas contaminant and providing an output signals indicative thereof, only in concurrence with said blockage signal indicating the pressure in said gas transport system being in excess of said preselected magnitude.