| 摘要 |
In a wavelength modulation spectroscopy method for measuring the concentration of a gas component in a gas sample a portion of the light of a tunable light source is passed through a reference gas comprising the gas component in a constant concentration. Afterwards the light is detected by a reference detector. Another portion of the light is passed through the gas sample and thereafter to a measuring detector. The light emitted by the light source is modulated with a frequency f<SUB>m</SUB>, while the wavelength is swept over a molecular absorption line of the gas component. Demodulation of the detector outputs is made at a higher harmonic Nf<SUB>m</SUB>. In order to compensate for variations of the modulation parameters of the light source ( 2 ) in real time, a mathematical description of the demodulated reference detector output (S(upsilon)<SUB>N,Ref</SUB>) based on Fourier analysis of the modulated light ( 1 ) and on a mathematical expression for the absorption line is provided, said mathematical description comprising unknown modulation parameters with respect to the modulation of the light ( 1 ). Said modulation parameters are determined from the demodulated reference detector output (S(upsilon)<SUB>N,Ref</SUB>) and its mathematical description. In a further step the concentration (c<SUB>Meas</SUB>) is determined from the demodulated measuring detector output (S(upsilon)<SUB>N,Meas</SUB>), a corresponding mathematical description of it and the modulation parameters.
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