Gas measurement device and gas measurement method

Abstract

After a measurement-target gas has been introduced into a measurement cell (40) to a predetermined pressure, a measurement by CRDS at a predetermined wavenumber is performed using a laser source unit (1), optical switch (3), optical resonator (4) and photodetector (5). A portion of the measurement-target gas is subsequently discharged from the measurement cell (40) to lower the pressure, and a measurement at the wavenumber of an absorption peak of the target component 14CO2 is performed. Since the influence of the absorption by 14CO2 in the measurement at high pressure is negligible, the concentration of the background, including 12CO2, can be determined from a ring-down time determined in this measurement. An absorption coefficient calculated from a ring-down time determined from measurement data acquired at low pressure contains an influence of the background, while the absorption coefficient of the background at low pressure can be determined from the concentration of the background determined at high pressure. Using this absorption coefficient, a concentration-computing operator (73) determines the absorption coefficient of only 14CO2 which is free from the influence of the background, and calculates the concentration of only 14CO2. Thus, based on the results of the two measurements performed at different pressures, an accurate absolute concentration of a target component, such as 14CO2, can be obtained. The measurement time can be shortened as compared to a conventional case.

Dependencies are inferred from the claim text.