Patent ID: 7251034

Claim:
A wavelength modulation spectroscopy method for measuring the concentration (c Meas ) of a gas component of interest in a gas sample, the method comprising the steps of: passing a portion of the light of a light source through a reference gas and thereafter to a reference detector, the reference gas comprising the gas component of interest or another suitable gas component in a known concentration; passing another portion of the light through the gas sample and thereafter to a measuring detector; modulating the wavelength of said light with a frequency (f m ), while the wavelength is swept over an absorption line of the gas component; demodulating the reference detector output (S(ν) Ref ) at a higher harmonic (Nf m ) of said frequency (f m ); providing a mathematical description of the demodulated reference detector output (S(ν) N,Ref ) based on Fourier analysis of the modulated light and on a mathematical expression for the absorption line, said mathematical description comprising unknown modulation parameters with respect to the modulation of the light; determining said modulation parameters from the demodulated reference detector output (S(ν) N,Ref ) and its mathematical description; and generating an output signal representative of the measurement.