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Procedia Engineering ProcediaProcedia Engineering 00 (2011) Engineering 26 000–000 (2011) 1200 – 1204 www.elsevier.com/locate/procedia
First International Sympos ium on Mine Safety Science and Engineering
Fiber Laser methane sensor and its application in coal mine safety Li Yan-fanga, b,Wei Yu-bina, b, Shang Yinga, b, Zhao Yan-jiea,b, Zhang Tingtinga, b,Wang Changa,b, Liu Tong-yua, b b
a Shandong Key Laboratory of Optical Fiber Sensor. Laser Institute of Shandong Academy of Sciences, Keyuan Road, Jinan, Shandong(250014),P.R. China
Abstract Using the technology of tuneable diode laser absorption spectroscopy and the technology of micro-electronics, a fiber laser methane sensor based on C8051F410 is given. We use the DFB Laser as the light source of the sensor. By tuning temperature and driver current of the DFB laser, we can scan the laser over the methane absorption line, we realize the methane detection. It makes the real-time and online detection of methane concentration to be true, and it has the advantages just as high accuracy, immun ity to other gases, long calibration cycle and so on. The sensor has the function of self-diagnose, the soft will alarm when the probe in a fault status, then it improve the dependence of the measurements. In coal mine safety, the proportion of gas accidents are improving continuously, Since for the coal mine safety, the personnel safety and the environment protection, it is very important to realize the real-time online detection of methane in coal mine. In this paper, some data that coming from the application of sensor in the field of coal mine is given. And we also do some analysis of the data. At last, according to the actual situation of the transducer in coal mine, we list some problems and the direction of further improvements.
© 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of China Academy of Safety Science and Technology, China University of Mining and Technology(Beijing), McGill University and University of Wollongong. Keywords: absortion spectroscopy; methane concentration; self-diagnose;coal mine safety
1. Introducti on As the development of the fiber technology and the semiconductor laser technology, the fiber gas sensor technology based on the spectroscopy absorption has the corresponding development. The fiber gas sensor has already become a frontier research field of the sensing technology. Compared with the The research is supported by eleven five Technology key support program (2009BAK54B01) E-mail:
[email protected]
1877-7058 © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2011.11.2291
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exit ing heat conduction methane sensor, the sensor has such advantages of high accuracy、immunity to other gases, long calibration cycle and so on. In coal mine safety and atmospheric environmental monitoring, etc, it realized the real-t ime and online detection of methane concentration. It has great significance to guarantee the safety of production and lives. In coal mine production, if we want to predict the spontaneous combustion and the water, it is very important to get the informat ion of the temperature, water degree, gas and the pressure, These disaster will cause serious damage to coal mine and the compound mining equip ment, even so it can induce coal mine safety accidents, then it can Cause serious economic loss. So it is very important to realize the detection of methane accurately. 2. Princi ple and Structure of the system 2.1 Principle of the system Based on the Beer-lambert law, When a monochro matic light wh ich intensity is
I 0 and wavelength is λ get through the sample gas, Based on Beer-Lambert law, the intensity of the outgoing light I , incident light I 0 and the Volu me concentration meet the following relationship: (1) I (λ ) = I 0 (λ ) exp(−α 0 (ν )CL) Where α 0 (ν ) is the absorption coefficient, C is the volu me concentration, L is the length of the absorption path. On the solution of (1), we can have:
C = ln( I 0
I
) αL
(2)
According the equation (2), we can get the gas concentration by the measurement of the light power and the optic path. For the optic path is fixed, so we can easily get the gas concentration by detect the power change before and after gas absorption. 2.2 Structure of the system According above mentioned Beer-lambert law, we designed a fiber laser methane sensor based on the MPU C8051F410.The functional block diagram are as follows figure 1.The sensor has a measure probe, and its measurement range can select fro m 0-4%, 0-40, 0-100%. In addit ion, there is a wavelength reference which can p rovide compensate to the effect of the environment temperature and so on. Temperature controller Sawtooth wave Current driver
fiber DFB
Opt ic sys
Photo detector MPU
AD acquisition
Data output Alarm Display
Sensor
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Li Yan-fang al. / Procedia Engineering 26 (2011) 1200 – 1204 Li Yan-fang et al/etProcedia Engineering 00 (2011) 000–000
Fig. 1 functional block diagram of the system
Considering the sensitivity, we choose the relative separate absorption line 1653n m as the absorption line. Through the temperature control circuit and current driver, we fixed the wavelength of the DFB on 1653n m. Optical part of the system main ly includes laser, Detectors as well as sensor. In the corresponding wavelength, the laser output power is greater than 3mW. We Select In GaAs detector to achieve Photo-electric Conversion, the Response wavelength range of which is 600n m-1700n m, and Responsiveness in the 1550n m is 0.85A / W. System use a fiber-coupled as the gas sensor, the optical path of its is about 10cm. The modulated optical signal is transmitted to the gas sensor through the singlemode fiber and fiber collimator. After absorption, the laser arrive photo-electric detector. The electric signals from detector transmitted to AD conversion, then to MPU. After data proceeding, the methane concentration is arrived, and the MPU output the frequency signal corresponding to concentration, Alarm signal and LED display. At the same time the sensor has RS485, through wh ich the data can be transmitted to computer, it can realize the self- d iagnose. 3. Experi ment and results Based on above mentioned sensor, We use the gas which concentration are 0.5, 1, 1.5, 3, 5, 8.53, 20, 30, 59.3, 70, 85 and clear N2 to the gas sensor respectively, we get the Calibration curve of the sensor just as the figure 2. To check the performance of the sensor, we used 0.5%, 8.5%, 20%, 30.5%, 59.3% and 85% methane to the sensor, and take a concentration value per 3s. Figure 3 shows the different concentrations results of the sensor. Figure 4, Figure 5 and Figure 6 give the methane concentration curve fro m applicat ion field of the mining face, the coal mine goaf and the ventilation air methane power generation respectively. 90
2 y = 9.8471x + 49.125x - 0.2431 2 R = 0.9991
80 70 60 50 40 30 20 10 0 0
Fig2. Calibration curve of the sensor
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Li ProcediaEngineering Engineering00 26 (2011) (2011) 000–000 1200 – 1204 Li Yan-fang Yan-fangetetal. al//Procedia
100 90 80 70 60 50 40 30 20 10 0 0
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Fig3.Display concentration curve of the sensor 3.00E-01
methane concentraion
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Fig4. Concentration curve from mining face
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Fig5. Concentration curve from coal mine goaf
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the concentration of CH4
0.12 0.1 0.08 0.06 0.04 0.02 0 -0.02
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sample points (one data per hour)
Fig6. Concentration curve from the ventilation air methane power generation
4. Conclusion These results indicate that the system can detect the methane of coal mine. It has the characteristics such as anti-electromagnetic interference, high accuracy and so on. The design of this instrument have played an important role in pro moting the use of optic fiber sensor at the coal mine, But after a long time, there are some faults such as the display value jumped, the laser power got weak and so on. So the next step our working will fix on the engineering problems of the sensor. References
[1] [2] [3] [4]
Deng Guangfu. Research on System of Gas Sensor Used in Mine Based on TDLAS[D]. Jilin University, 2008. Li yanfang, Wei yubin, Wang zhe, Zhao yanjie, Shang ying, Liu tongyu, “Fiber methane gas detection device and its application in methane extraction electricity generation”[J], Shandong Science, pp: 1-3, 2008(6). Wei yubin, Li yanfang, Shang ying, Zhang tingting, Song zhiqiang, Wang chang, Liu tongyu“ Fiber optic TDLAS-based mutigas remote detection system for mine goaf fire”, The 5th SPIE International Symposium on Advanced Optical Manufacturing and Testing Technologies. China, Dalian, 2010.4. Liang Yun-tao .Gas index method to predict coal spontaneous combustion[J]. COAL SCIENCE AND TECHNOLOGY , 2008;36:5-8.
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