Abstract
A laser-based hydrogen (H2) sensor using wavelength modulation spectroscopy (WMS) was developed for the contactless measurement of molecular hydrogen. The sensor uses a distributed feedback (DFB) laser to target the H2 quadrupole absorption line at 2121.8 nm. The H2 absorption line exhibited weak collisional broadening and strong collisional narrowing effects. Both effects were investigated by comparing measurements of the absorption linewidth with detailed models using different line profiles including collisional narrowing effects. The collisional broadening and narrowing parameters were determined for pure hydrogen as well as for hydrogen in nitrogen and air. The performance of the sensor was evaluated and the sensor applicability for H2 measurement in a range of 0–10 %v of H2 was demonstrated. A precision of 0.02 %v was achieved with 1 m of absorption pathlength (0.02 %v∙m) and 1 s of integration time. For the optimum averaging time of 20 s, precision of 0.005 %v∙m was achieved. A good linear relationship between H2 concentration and sensor response was observed. A simple and robust transmitter–receiver configuration of the sensor allows in situ installation in harsh industrial environments.
Highlights
An increased demand for hydrogen gas sensors is strongly coupled with the expanded use of hydrogen gas (H2 ) in industry [1,2]
Sensors 2019, 19, 5313 electric quadrupole transitions [4], which is why laser-based detection of H2 so far has been limited to extractive cavity-enhanced sensors based on cavity ring-down spectroscopy (CRDS) [5,6], intra-cavity output spectroscopy (ICOS) [7,8], and optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) [9]
The simulation using have been implemented profile (HTP) with the line strength listed in High-resolution molecular absorption (HITRAN) and the collisional parameters obtained in this study for H2 in nitrogen and air indicates that 1 %v H2 over a 1-m optical pathlength
Summary
An increased demand for hydrogen gas sensors is strongly coupled with the expanded use of hydrogen gas (H2 ) in industry [1,2]. Many different types of hydrogen safety sensors are commercially available [3], and the common principle is a sensing element that is altered (e.g., by resistance) when in contact with hydrogen This mode of operation precludes the use of these point-type hydrogen sensors in reactive, corrosive, and/or dusty gas streams. Sensors 2019, 19, 5313 electric quadrupole transitions [4], which is why laser-based detection of H2 so far has been limited to extractive cavity-enhanced sensors based on cavity ring-down spectroscopy (CRDS) [5,6], intra-cavity output spectroscopy (ICOS) [7,8], and optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) [9] Common in these techniques is confinement of the laser light in a high-finesse optical cavity by using a set of highly reflective mirrors. Using a response time of 1 s, an estimated limit of detection (LOD) for H2 of 0.1 %v for 1 m of absorption pathlength was achieved
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