Patent ID: 7187178

Claim:
A method for determining the voltage sensitivity of a distance between the mirrors in a Fabry-Perot interferometer (FPI), which is intended to measure an absorption value of a predefined gas, of which at least one absorption maximum (ABS) or minimum is known, the method including the steps of: defining at least two device-specific calibration points using a reference gas in controlled conditions, in such a way that at least one of the calibration points (ABS) includes information on a control-voltage signal pair for one absorption maximum (ABS) of the gas being measured, and another of the calibration points (ABS) being a corresponding control-voltage signal pair for a reference measurement (REF), and defining a corresponding signal-control-voltage for the absorption value of the predefined gas being measured, forming a ‘virtual’ signal-control voltage sensitivity curve, with the aid of the calibration points formed using a reference gas, measuring absorption signal value(s) in the vicinity of the preselected absorption maximum (ABS) and/or minimum, in the presence of the gas being measured, forming ratio(s) of the absorption signal values of the gas being measured and the absorption signal values of the reference gas, and a control voltage value corresponding to at least one minimum or maximum is defined from the ratio(s), in which case, on the basis of wavelengths of the absorption minima or maxima of the gas being measured, the voltage sensitivity of the distance between the mirrors is defined unequivocally and corrections are made to FPI voltage values (Vabs, Vref).