Patent ID: 6353225
Filing Date: 2002-03-05
Classification: G01N

Abstract:
A method for selectively detecting and measuring the concentration of a gas through light absorption in the near infrared region, the gas emitting a spectrum with a plurality of spectral lines upon being exposed to light in the near infrared region, the method comprising the following steps:selecting at least one spectral line of the spectrum of the gas to be detected, selecting a distributed feed back laser diode with a range of emission wavelengths in the near infrared region that is dependent upon an operating temperature of the laser diode greater than or equal to 40Â° C. and that encompasses the selected spectral line, emitting light having an emission wavelength in the near infrared region from the laser diode across a measuring distance to a photodetector, detecting the gas by monotonically increasing the operating temperature of the laser diode in a range starting at least at 40Â° C. so that the emission wavelength of the light emitted from the laser diode monotonically increasingly sweeps said range of emission wavelengths thereby insuring coverage of the spectral line of the gas to be detected, and measuring the concentration of the gas by measuring an absorption difference at the photodetector in a wavelength region corresponding to the selected spectral line at two different operating temperatures of the laser diode in said sweep and calculating the concentration of the gas to be measured from the absorption difference.