Patent ID: 7180595
Filing Date: 2007-02-20
Classification: G01N

Abstract:
1. Gas detection method comprising the following steps of providing an initial light signal, by a wavelength modulated laser source, said initial light signal is wavelength modulated at a first frequency symmetrically around an absorption line of a gas the concentration or presence of which is to be determined; passing said initial light signal having intensity variations over the time resulting from an alternative scanning around said gas absorption line through a gas detection region intended for receiving at least one of said gases; receiving a resulting light signal exciting said gas detection region, by detection means, said resulting light signal comprises changes in the intensity of the initial light signal due to the gas concentration in the detection region; generating a detection signal by said detection means being substantially proportional to the time derivate of said resulting light signal; generating a first measuring signal from said detection signal, which is a function of intensity of said initial light signal; generating a second measuring signal from said detection signal, which is a function of the gas absorption and substantially independent of an intensity modulation of said initial light signal at said first frequency providing a final measuring signal being independent from the intensity of light incident onto the detection means by dividing said second measuring signal by said first measuring signal and thereby providing a signal relative to the presence or the concentration of a given gas.