Study on Calibration-Free Measurement Method for Gas Concentration Based on Triangular Wave Modulation

Bubin Wang; Bin Zhou; Hao Wang; Yongquan Xiong; Yihong Wang; Yangkun Zhu; Shimin Wang

doi:10.3788/AOS201737.0930003

Acta Optica Sinica, Volume. 37, Issue 9, 0930003(2017)

Study on Calibration-Free Measurement Method for Gas Concentration Based on Triangular Wave Modulation

Bubin Wang, Bin Zhou, Hao Wang, Yongquan Xiong, Yihong Wang, Yangkun Zhu, and Shimin Wang

Author Affiliations

School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, China

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Figures & Tables(14)

Fig. 1. Flow chart of calibration-free wavelength modulation inversion algorithm for concentration

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Fig. 2. (a) Amplitudes of triangle waveform and simplified waveform; (b) relative residual

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Fig. 3. Measured and fitted frequency response of sine wave scanning superimposed by triangular wave modulation for DFB laser. (a) discrete points of laser frequency response and fitted curve of scanning term; (b) discrete points and fitted curve of frequency response of modulation term and coupling term; (c) relative residual between discrete points and fitted curves of modulation term and coupling term

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Fig. 4. Schematic of experimental apparatus for measuring CH4 concentration without calibration

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$Background light intensity signal and absorption signal of CH4 with mole fraction of 4.00%$

Fig. 5. Background light intensity signal and absorption signal of CH4 with mole fraction of 4.00%

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$(a) Second harmonic signals of SM2f for triangle wave modulation and sine wave modulation at optimal modulation parameters; (b) experimental SM2f/1f and simulated SS2f/1f for CH4 with mole fraction of 4.00%; (c) relative residual between simulated SS2f/1f and experimental S2f/1fM$

Fig. 6. (a) Second harmonic signals of SM2f for triangle wave modulation and sine wave modulation at optimal modulation parameters; (b) experimental SM2f/1f and simulated SS2f/1f for CH4 with mole fraction of 4.00%; (c) relative residual between simulated SS2f/1f and experimental S2f/1fM

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$(a) Measured mole fraction of 4.00%CH4 in 600 s; (b) Allan variance$

Fig. 7. (a) Measured mole fraction of 4.00%CH4 in 600 s; (b) Allan variance

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$Measured mole fraction of CH4 in mixture gas of CH4 and N2$

Fig. 8. Measured mole fraction of CH4 in mixture gas of CH4 and N2

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$Measured mole fraction of CH4 in mixture gas of CH4, N2 and CO2$

Fig. 9. Measured mole fraction of CH4 in mixture gas of CH4, N2 and CO2

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Table 1. Fourier expanding coefficients Ai and ratio (Ki) of Ai to A1
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Table 1. Fourier expanding coefficients Ai and ratio (Ki) of Ai to A1
i 1 2 3 4 5 6 7 8 9 10
A_i 0.8105 0.0900 0.0324 0.0165 0.0100 0.0066 0.0047 0.0036 0.0028 0.0022
K_i 100.00 11.111 4.000 2.040 1.234 0.826 0.591 0.444 0.346 0.277

Table 2. Parameters of fitting results of V(t)
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Table 2. Parameters of fitting results of V(t)
Coefficient 1^st harmonic 2^nd harmonic 3^rd harmonic
a_s,_i 2.96×10^-1 -5.56×10^-3 ^*-5.07×10^-4
a_m,_i -1.56×10^-1 3.81×10^-3 ^*-1.09×10^-4
b_m,_i 1.51×10^-2 ^*-3.32×10^-5 ^*3.52×10^-5

Table 3. Main parameters of selected spectral lines
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Table 3. Main parameters of selected spectral lines
$\begin{matrix} {ν_{0}}_{} \end{matrix}$ /cm^-1 S(296 K) /(cm^-2·Pa^-1) E /cm^-1
6046.94195 2.000×10^-7 62.8758
6046.95275 2.454×10^-7 62.8768
6046.96474 3.227×10^-7 62.8782

Table 4. Distribution list for different mole fractions of CH4(CH4/N2)

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Table 4. Distribution list for different mole fractions of CH4(CH4/N2)

CH₄ mole fraction /%	CH₄ flow /(L·min^-1)	N₂ flow /(L·min^-1)	Total flow /(L·min^-1)
0.80	0.20	0.80	1.00
1.00	0.25	0.75	1.00
1.60	0.40	0.60	1.00
2.00	0.50	0.50	1.00
2.40	0.60	0.40	1.00
3.00	0.75	0.25	1.00
3.20	0.80	0.20	1.00
4.00	1.00	0.00	1.00

Table 5. Distribution list for different mole fractions of CH4 (CH4/N2/CO2)

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Table 5. Distribution list for different mole fractions of CH4 (CH4/N2/CO2)

Mole fraction /%		CH₄ flow /(L·min^-1)	CO₂ flow /(L·min^-1)	Total flow /(L·min^-1)
		CH₄ flow /(L·min^-1)	CH₄	CO₂
0.80	80	0.20	0.80	1.00
1.00	75	0.25	0.75	1.00
1.60	60	0.40	0.60	1.00
2.00	50	0.50	0.50	1.00
2.40	40	0.60	0.40	1.00
3.00	25	0.75	0.25	1.00
3.20	20	0.80	0.20	1.00
4.00	0	1.00	0.00	1.00

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Bubin Wang, Bin Zhou, Hao Wang, Yongquan Xiong, Yihong Wang, Yangkun Zhu, Shimin Wang. Study on Calibration-Free Measurement Method for Gas Concentration Based on Triangular Wave Modulation[J]. Acta Optica Sinica, 2017, 37(9): 0930003

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