Wavelength modulation spectroscopy with signal–reference beam method for highly sensitive gas detection

Wei, Wei; Chang, Jun; Huang, Qingjie; Zhu, Cunguang; Wang, Qiang; Wang, Zongliang; Lv, Guangping

doi:10.1007/s00340-014-5956-1

Cited by 17 publications

(8 citation statements)

References 17 publications

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“…Wei W et al used wavelength modulation spectroscopy combined with signal-reference beam method for trace gas detection, which not only achieved common-mode noise suppression but also improved the SNR. The measurement accuracy of the system can reach 1 ppm for an optical path length of 10 cm verified by trace water vapor detection experiments [81]. Wang F et al have expanded the functionality of the phase-locked amplification technique, which can accurately measure the phase information from the extremely weak signal.…”

Section: Signal Demodulationmentioning

confidence: 98%

Improvement of the Detection Sensitivity for Tunable Diode Laser Absorption Spectroscopy: A Review

et al. 2022

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Tunable Diode Laser Absorption Spectroscopy (TDLAS), a trace gas sensing technology based on infrared absorption spectroscopy, has been developed rapidly in the past few decades. The advantages of low cost and easy miniaturization could be applied in real-time monitoring. As an important factor, the detection sensitivity of TDLAS has been improved by a variety of methods. In this review paper, the important advances in TDLAS detection sensitivity are discussed, including the selection of absorption lines, the improvement of diode lasers, the design of effective optical paths, data demodulation, and the suppression of background interference. For gases with high application values, such as CH4, CO2, and NO, we summarize the detection sensitivity that the existing TDLAS system has been achieved, combined with the above-improved process. However, considering the principle of infrared absorption, the increase in detection sensitivity could reach an ultra-limit. Therefore, the hypothesis of the sensitivity limit of TDLAS is proposed at the end of the paper, through the quantization analysis.

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Section: Signal Demodulationmentioning

confidence: 98%

Improvement of the Detection Sensitivity for Tunable Diode Laser Absorption Spectroscopy: A Review

et al. 2022

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“…Our system for trace measurement of water vapor used a distributed feedback laser diode (DFB-LD; (Carlisle and Cooper, 1990;Duffin et al, 2007;Wei et al, 2015;Ruxton et al, 2010). An overlapped mixed signal containing a sinusoidal modulation signal and 7.8-Hz-trapezoidal scanning signal for the DFB-LD [Figure 5(a)] was generated by an ARM7 processor (LTC1758, NXP, The Netherlands).…”

Section: Linear Fittingmentioning

confidence: 99%

“…The signal amplitude of the second harmonic can be measured with a lock-in amplifier (LIA), which is proportional to the concentration. An important advantage of this technique is to shift the detection to higher frequencies, at which the laser excess noise (1/f noise) can be reduced (Wang, 2007;Duffin et al, 2007;Wei et al, 2015;Cao et al, 2010;Wang et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Water vapor concentration measurements using TDALS with wavelength modulation spectroscopy at varying pressures

Wei

Chang

Huang

et al. 2017

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Purpose As measurement results of optical gas sensors are constantly affected by the pressure of a target gas, approaches must be taken to modify the results. The purpose of this paper is to compare the traditional measurement method with the new measurement system. At the same time, measurement results of the two systems under different pressures are presented for comparison of the detection performance. Design/methodology/approach A theoretical model of line shape function and its impact on the measured results is presented, which is based on direct absorption and wavelength modulation spectroscopy (WMS) for gas concentration detection under different pressures. Methods of linear fitting and result modification have been illustrated and compared. A new testing system with the result modification method used for water vapor concentration detection under different pressures between 1 and 7 atm is applied. With an additional pressure sensor placed in the gas cell and calibration performed, relationships between the amplitude of the second harmonic and concentration of the target gas under different pressures can be obtained. Findings Amplitude detection can be used for concentration detection regardless of the change in pressure for the method of direct absorption. Although, WMS with second harmonic detection is not enough. Two methods are presented and compared with WMS under different pressures. Moreover, the result modification method shows better performance as computation is significantly reduced. Originality/value The comparison between linear fitting and the result modification method with WMS under different pressures is firstly presented. At the same time, a new testing system with better performance for water vapor concentration detection under different pressures is presented as well.

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“…TDLS with wavelength modulation spectroscopy (WMS) enables alternating-current (AC) detection at some frequency of choice and the use of a lock-in amplifier (LIA) for better signal recovery [ 17 , 18 , 19 , 20 ]. Each harmonic signal is proportional to the concentration of target gas and can be measured with the LIA.…”

Section: Introductionmentioning

confidence: 99%

Modulation Index Adjustment for Recovery of Pure Wavelength Modulation Spectroscopy Second Harmonic Signal Waveforms

Wei

Chang

Wang

et al. 2017

Sensors

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A new technique of modulation index adjustment for pure wavelength modulation spectroscopy second harmonic signal waveforms recovery is presented. As the modulation index is a key parameter in determining the exact form of the signals generated by the technique of wavelength modulation spectroscopy, the method of modulation index adjustment is applied to recover the second harmonic signal with wavelength modulation spectroscopy. By comparing the measured profile with the theoretical profile by calculation, the relationship between the modulation index and average quantities of the scanning wavelength can be obtained. Furthermore, when the relationship is applied in the experimental setup by point-by-point modulation index modification for gas detection, the results show good agreement with the theoretical profile and signal waveform distortion (such as the amplitude modulation effect caused by diode laser) can be suppressed. Besides, the method of modulation index adjustment can be used in many other aspects which involve profile improvement. In practical applications, when the amplitude modulation effect can be neglected and the stability of the detection system is limited by the sampling rate of analog-to-digital, modulation index adjustment can be used to improve detection into softer inflection points and solve the insufficient sampling problem. As a result, measurement stability is improved by 40%.

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Wavelength modulation spectroscopy with signal–reference beam method for highly sensitive gas detection

Cited by 17 publications

References 17 publications

Improvement of the Detection Sensitivity for Tunable Diode Laser Absorption Spectroscopy: A Review

Improvement of the Detection Sensitivity for Tunable Diode Laser Absorption Spectroscopy: A Review

Water vapor concentration measurements using TDALS with wavelength modulation spectroscopy at varying pressures

Modulation Index Adjustment for Recovery of Pure Wavelength Modulation Spectroscopy Second Harmonic Signal Waveforms

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