Patent ID: 7586613

Claim:
A method for self-diagnostic checking or self-adjustment of an optical gas concentration measurement device, the method comprising steps for directing narrow-band light to gas to be measured and measuring attenuation of the light in the gas, modulating a center wavelength of the light source around or over a first predetermined absorption maximum ( 10 ) (absorption line) of the measured gas, measuring the attenuation of the light in the gas as a function of the center wavelength of the light, determining gas concentration based on the measurement, varying the center wavelength of the light such that the center wavelength is adapted to coincide with at least one other absorption maximum ( 11 ) (peak) with different absorption properties of the gas to be measured,—measuring correspondingly the attenuation of the other absorption maximum or maxima ( 11 ) as a function of the center wavelength of the light, defining the light source ( 1 ) control signals required to vary the wavelength to the said first absorption maximum and said other absorption maxima, and using the defined properties of the light source control signals and/or measured attenuation information of said other absorption maxima for self-diagnostic checking of the device.