Absorption spectrometer and method for measuring the concentration of a gaseous component of interest in a measurement gas

An absorption spectrometer for measuring the concentration of a gaseous component of interest in a measurement gas, comprising:

• a variable-wavelength laser;
• a detector for generating a measurement signal;
• a multi-reflection gas cell arranged in a light path between the variable-wavelength laser and the detector and containing the measurement gas;
• a controller configured to vary an injection current (i) of the variable-wavelength laser and to tune the wavelength of light to a specific absorption line of the gaseous component of interest, the controller including at least one pilot signal generator to modulate the injection current (i) alternately or simultaneously with at least two pilot frequencies (fP1, fP2) in a MHz range;
• an analyzer configured to analyze the measurement signal and establish a measured result for a concentration to be measured;
• and
• a further analyzer configured to analyze each signal component of at least two signal components contained in the measurement signal with the at least two pilot frequencies (fP1, fP2) in a phase-sensitive manner, to determine a length (Lmeas) of the light path from a difference (Δφmeas) between items of phase information (φ1, φ2) of the at least two signal components obtained in this operation, to compare said determined length with a length (Lcalib) obtained during calibration of the absorption spectrometer or a known length (L0) of the light path, and to correct the measured result as a function of a relationship between the two lengths (Lmeas, Lcalib or L0).

An absorption spectrometer for measuring the concentration of a gaseous component of interest in a measurement gas, comprising:

• a variable-wavelength laser;
• a detector for generating a measurement signal;
• a multi-reflection gas cell arranged in a light path between the laser and the detector and containing the measurement gas;
• a controller configured to vary an injection current (i) of the variable-wavelength laser and to tune a wavelength of the light to a specific absorption line of the gaseous component of interest, the controller including at least one pilot signal generator to modulate the injection current (i) alternately or simultaneously with at least two pilot frequencies (fP1, fP2) in a MHz range;
• an analyzer configured to analyze the measurement signal and establish a measured result for a concentration to be measured;
• and
• a further analyzer configured to analyze each signal component of at least two signal components contained in the measurement signal with the at least two pilot frequencies (fP1, fP2) in a phase-sensitive manner and to determine a length (Lmeas) of the light path from a difference (Δφmeas) between items of phase information (φ1, φ2) of the at least two signal components obtained in this operation, with the aid of which the measured result is immediately determined from an absorption represented by the measurement signal.

A method for measuring the concentration of a gaseous component of interest in a measurement gas, comprising:

• tuning a wavelength of light from a laser to a specific absorption line of the gaseous component of interest;
• routing modulated light through a multi-reflection gas cell containing the measurement gas onto a detector;
• analyzing a measurement signal generated by the detector to establish a measured result for a concentration to be measured;
• modulating the light from the laser alternately or simultaneously with at least two pilot frequencies (fP1, fP2) in a MHz range;
• analyzing each signal component of at least two signal components contained in the measurement signal with the at least two pilot frequencies (fP1, fP2) in a phase-sensitive manner;
• comparing a difference (Δφmeas) between items of phase information (φ1,φ2) of the at least two signal components obtained during said analyzing with a difference (Δφcalib) between items of phase information obtained during calibration of the absorption spectrometer;
• and
• correcting the measured result as a function of the relationship between the two differences (Δφmeas, Δφcalib).

A method for measuring a concentration of a gaseous component of interest in a measurement gas, comprising:

• tuning a wavelength of light from a laser to a specific absorption line of the gaseous component of interest;
• routing modulated light through a multi-reflection gas cell containing the measurement gas onto a detector;
• analyzing a measurement signal generated by the detector to establish a measured result for a concentration to be measured;
• modulating the light from the laser alternately or simultaneously with at least two pilot frequencies (fP1, fP2) in a MHz range;
• analyzing each signal component of at least two signal components contained in the measurement signal with the at least two pilot frequencies (fP1, fP2) in a phase-sensitive manner;
• determining a length (Lmeas) of the light path from a difference (Δφmeas) between items of phase information (φ1, φ2) of the at least two signal components obtained during said analyzing;
• comparing said determined length with a length (Lcalib) obtained during calibration of the absorption spectrometer or a known length (L0) of the light path;
• and
• correcting the measured result as a function of a relationship between the two lengths (Lmeas, Lcalib or L0).

A method for measuring a concentration of a gaseous component of interest in a measurement gas, comprising:

• tuning a wavelength of light from a laser to a specific absorption line of the gaseous component of interest;
• routing modulated light through a multi-reflection gas cell containing the measurement gas onto a detector;
• analyzing a measurement signal generated by the detector to establish a measured result for a concentration to be measured;
• modulating the light from the laser alternately or simultaneously with at least two pilot frequencies (fP1, fP2) in a MHz range;
• analyzing each signal component of at least two signal components contained in the measurement signal with the at least two pilot frequencies (fP1, fP2) in a phase-sensitive manner;
• determining a length (Lmeas) of the light path from a difference (Δφmeas) between items of phase information (φ1, φ2) of the at least two signal components obtained during said analyzing;
• and
• establishing the measured result immediately with the determined length from an absorption represented by the measurement signal.

A method for measuring a concentration of a gaseous component of interest in a measurement gas, comprising:

• tuning a wavelength of light from a laser to a specific absorption line of the gaseous component of interest;
• routing a modulated light through a multi-reflection gas cell containing the measurement gas on to a detector;
• analyzing a measurement signal generated by the detector to establish a measured result for a concentration to be measured;
• modulating the light from the laser with at least one pilot frequency (fP) in a MHz range;
• analyzing the measurement signal for a pilot frequency (fP) in a phase-sensitive manner;
• comparing phase information (αmeas) obtained during said analyzing with phase information (αcalib) obtained during calibration of the absorption spectrometer;
• and
• correcting the measured result as a function of a difference (Δα) between the two items of phase information (αmeas, αcalib);
• wherein, in a case of modulation of the light with phase-sensitive analysis of the measurement signal with a plurality of pilot frequencies, one pilot frequency is selected at a level high enough such that in the case of a maximum tolerable change in an optical path distance between the laser and the detector, obtained phase information changes by more than k·π (k≧1), and another pilot frequency is selected at a level low enough such that in the case of the maximum tolerable change in the optical path distance, the obtained phase information changes by less than π, and such that a value k in the phase information from a higher pilot frequency is determined based on phase information from a lower pilot frequency.