Patent ID: 6878339

Claim:
A NOx-concentration measuring apparatus for quantitatively analyzing the concentration of NOx contained in a sample gas, comprising: a sampling probe for obtaining the sample gas; a drain separator for condensing moisture contained in the sample gas as a condensed water and separating the condensed water from the sample gas, said drain separator having a cooling device therein for cooling the sample gas; an NO 2 converter for converting NO 2 contained in the sample gas into NO; a secondary cooling device for additionally cooling the sample gas; and an NO analyzer, arranged in above stated order with respect to a sample-gas line of said NOx-concentration measuring apparatus, wherein said drain separator is operable to cool the sample gas passing therethrough at a high flow velocity such that a ratio of the flow rate (cm 3 /min) of said sample gas passing through said drain separator to the internal volume (cm 3 ) of said drain separator is set at 10 (min −1 ) or more; and the sample-gas line between said sampling probe and said drain separator is heated and/or thermally insulated over the entire length thereof.