Hydrogen is an important source used as an energy carrier and a chemical reactant or industrial material. However, if not handled properly, hydrogen content as low as 4% can lead to a life-threatening catastrophe. Hydrogen sensors with higher sensitivity, better selectivity, faster response, and wider dynamic range are of increasing importance in connection with the development. In this paper, a scheme of hydrogen sensor that satisfies these requirements with a single sensing element is proposed which is centered on a nanofiber. The sensor is based on stimulated Raman scattering spectroscopy but the tightly confined evanescent field associated with the nanofiber enhances the Raman gain per unitlength by a factor of more than 104 over free-space beams. In addition, the homemade signal processing circuit plays an important role in the whole sensing system instead of the commercial instruments, which makes it possible to develop a principle prototype. The circuit intergrates tne DFB laser driver circuit, the photoelectric detection circuit and the main control circuit which outputs modulation signal and acts as a digital lock-in amplifier. Several silica nanofibers operating in the telecom wavelength band has been manufactured and measured in an experiment that demonstrates hydrogen detection from hundreds parts per million to 100%. The reported sensor could be used in the field of new energy, electric power and aerospace for detection of hydrogen leakage or monitoring of transformer health conditions with advantages of low cost, small size and outstanding performance.
Natural gas and biogas, as commonly used combustible gases, are widely used in urban residents and industrial enterprises. Gas leakage accidents occur frequently. In order to more accurately distinguish whether it is a natural gas leak or a biogas leak, this paper proposes a method for simultaneous detection of methane and ethane based on TDLAS, and develops a set of methane and ethane dual gas detection devices. Firstly, this paper studied the gas absorption lines of methane and ethane. According to the absorption lines, a 1680nm DFB laser beam was used to scan methane and ethane at the same time. Secondly, the phase-locked amplifier module of TDLAS technology is used to obtain the second harmonic signals of methane and ethane concentration detection at the same time, and identify the components of methane and ethane based on the peak position information and FWHM information of the second harmonic signal. Finally, the concentration calculation function is obtained by fitting the peak and valley difference of the second harmonic. Experimental results show that the detection method and device proposed in this paper can achieve simultaneous detection of methane and ethane
The characteristic absorption lines of carbon monoxide gas cross with that of other gases in near-infrared and midinfrared bands, the detection results are easily disturbed. Especially in some environments such as coal mines and petrochemicals, it is more important to avoid cross interference, in order to achieve accurate measurement of carbon monoxide. In this paper, a DFB laser beam at 2330nm was selected and scanned for absorption line of carbon monoxide. Although interference of other gas components was avoided, the overlap of carbon monoxide and methane spectra still existed. Firstly, the absorption lines of methane and carbon monoxide were studied. According to the theory of molecular spectroscopy, the FWHM of methane and carbon monoxide absorption lines are different. Once, there is methane gas in the background, the harmonic signals will be different due to different line shape. The second harmonic signals with different modulation coefficients are simulated. So the troughs width is selected as the evaluation function of the harmonic signal characteristics for component judgement. Secondly, after component determination, when mixed gas is present, adjacent methane absorption peaks are also scanned for deduction. The influence of temperature is also calculated and the evaluation function is modified again. Finally, the free calibration measurement of carbon monoxide concentration in the mixture is realized. In summary, for the working conditions of complex background gas such as coal mine and petrochemical. This paper presents a calibration-free method for reliable carbon monoxide concentration detection based on a TDLAS technique.
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