Hydrogen gas sensor and method for measurement of hydrogen under ambient and elevated pressure
Gas sensor capable for in-situ non-contact optical measurements of hydrogen gas (H2) and method for measuring hydrogen gas under ambient and elevated pressures without the need for cells with extremely long optical path length. The gas sensor can be configured for dual gas measurements such as H2 and CO2.
1. Gas analyzer based on tuneable laser spectroscopy for measurement of concentration of Hydrogen gas, H2, in a target gas ( 500 ) comprising a gas matrix possibly comprising interfering gases, the analyzer comprising a transmitter part ( 600 ) and a receiver part ( 650 ), the transmitter part ( 600 ) comprising a tunable laser ( 2000 ) arranged for emitting laser light in the form of a laser beam ( 2100 ), the laser beam ( 2100 ) following an optical path, a processing unit ( 2700 ) performing housekeeping including means for laser tuning and laser modulation, wavelength of the laser light being tuned across an absorption line of the at least one gas component to be measured, the laser beam ( 2100 ) passing through the target gas ( 500 ) and onto a light sensitive detector ( 2500 ) comprised by the receiver part ( 650 ), the light sensitive detector generating an absorption signal ( 2510 ) possibly comprising an absorption signal contribution from the gas component to be measured and from the interfering gases, a digitization unit ( 2600 ) digitizing the absorption signal ( 2510 ), the digitized absorption signal from the digitization unit ( 2600 ) being inputted to the processing unit ( 2700 ), the processing unit ( 2700 ) performing calculation of the measured concentration of gas component to be measured in the target gas ( 500 ) based on the digitized absorption signal, the analyzer characterised by the wavelength of the laser light being tuned across an H2 absorption line near 2122 nm, the gas analyzer further comprising a sealed reference gas cell ( 550 ) comprising an other gas than H2 with at least one absorption line spectrally adjacent to the absorption line of H2, so that the laser light is tuned across the H2 line and across the line of said gas in the reference gas cell, the analyzer being suitable for wavelength modulation spectroscopy, WMS, or digital wavelength modulation spectroscopy, dWMS, the processing unit ( 2700 ) applying to the laser a higher frequency modulation of the wavelength, wherein amplitude of the said wavelength modulation is set to approximately match the H2 absorption line width so as to retain the H2 WMS absorption signal and to suppress WMS absorption signals from said possible interfering gases having broader absorption lines than the H2 line, the processing unit ( 2700 ) applying a digital filter of a higher order digital filter type to the digitized WMS signal wherein the filter is adapted to pass through the H2 WMS signal and to suppress the WMS signal from the possible interfering gases, the processing unit ( 2700 ) calculating the concentration of hydrogen gas component based on the filtered signal, and verifying the signal from the other said gas contained in the reference cell so as to control the laser tuning over a wavelength interval comprising the absorption line of H2.
2. Gas analyzer according to claim 1 , wherein the reference gas cell ( 550 ) is permanently arranged in the optical path.
3. Gas analyzer according to claim 2 , wherein the processing unit, based on information from the reference gas cell, controlling the laser tuning such that to position the centre of the H2 absorption line in the absorption signal at the same position relatively to the laser tuning range.
4. Gas analyzer according to claim 3 , wherein the processing unit, based on information from the reference gas cell, adjusting the laser tuning range such that the positions of the absorption lines are kept approximately in the same positions relatively to the sampled region and such that the laser tuning is kept linear or in an arbitrary predefined way of tuning.
5. Gas analyzer according to claim 1 , wherein the reference gas cell ( 550 ) is arranged for being flipped in and out of the optical path depending on required function such that the cell is flipped out for measuring the gas concentrations and the cell is flipped in for verifying the signal.
6. Gas analyzer according to claim 5 , wherein the processing unit, based on information from the reference gas cell, controlling the laser tuning such that to position the centre of the H2 absorption line in the absorption signal at the same position relatively to the laser tuning range.
7. Gas analyzer according to claim 6 , wherein the processing unit, based on information from the reference gas cell, adjusting the laser tuning range such that the positions of the absorption lines are kept approximately in the same positions relatively to the sampled region and such that the laser tuning is kept linear or in an arbitrary predefined way of tuning.
8. Gas analyzer according to claim 1 , wherein the processing unit ( 2700 ), based on information from the reference gas cell ( 550 ), controlling the laser tuning such that to position the centre of the H2 absorption line in the absorption signal at the same position relatively to the laser tuning range.
9. Gas analyzer according to claim 8 , wherein the processing unit ( 2700 ), based on information from the reference gas cell ( 550 ), adjusting the laser tuning range such that the positions of the absorption lines are kept approximately in the same positions relatively to the sampled region and such that the laser tuning is kept linear or in an arbitrary predefined way of tuning.
10. Gas analyzer according to claim 1 , wherein the reference cell ( 550 ) comprising the other gas, the other gas being N2O.
11. Gas analyzer according to claim 1 , wherein the wavelength modulation amplitude is set to approximately 2.2 times the half width half max, HWHM, of the H2 absorption line in the target gas.