Tunable diode laser absorption spectroscopy (TDLAS) technique has been widely investigated for gas concentration measurement in both industry and laboratory. In order to detect different gases within the multi-gas mixture based on TDLAS, different types of schemes have been developed, such as wavelength division multiplexing, time division multiplexing and so on. However, there are many drawbacks of the above methods, and the sensitivity and accuracy of multi-gas detection have been greatly restricted, the effect of cross-talking interferences becomes a technical bottleneck for multi-gas detection. Therefore, a high accuracy synchronous detection technology for multi-gas detection using the least square fitting is reported. The wavenumber of 6380cm-1 has been selected to detect CO and CH4. Because the absorptivity of CH4 and CO is less than 0.1, the least square fitting method can be used to calculate the concentrations of CH4 and CO simultaneously. This novel method has been shown to improve the precision achieved in the detection of multi-gas by 18%, compared with the precision measured at another wavelength. The Allan variance results indicate that the optimal integration time has been improved from 50s to 100s, the minimum measurement precision of CH4 and CO is ~0.45% and ~0.46 10-6 respectively. Meanwhile, the detection cost and response time can be reduced obviously.
This paper discusses the research progress of low-power technology of laser methane sensors for coal mine. On the basis of environment of coal mines, such as ultra-long-distance transmission and high stability, a series of studies have been carried out. The preliminary results have been achieved in the research of low power consumption, temperature and pressure compensation and reliability design. The technology is applied to various products in coal mines, and achieves high stability and high reliability in products such as laser methane sensor, laser methane detection alarm device, wireless laser methane detection alarm device, and optic fiber multichannel laser methane sensor. Experimental testing and analysis of the characteristics of laser methane sensors, combined with the actual application.
The coal industry plays an important role in the economic development of China. With the increase of coal mining year by year, coal mine accidents caused by gas explosion also occur frequently, which poses a serious threat to the life safety of absenteeism and national property safety. Therefore, high-precision methane fiber sensor is of great significance to ensure coal mine safety. This paper mainly introduces two kinds of quasi-distributed gas optical fiber sensing systems based on laser absorption spectroscopy. The gas fiber optic sensor based on absorption spectrum has high measurement accuracy, fast response and long service life. One is quasi-distributed optical fiber sensing system based on spatial division multiplexing (SDM) technology and the other is quasi-distributed optical fiber sensing system based on optical time domain reflection and time division multiplexing(TDM) technology.
As the most important characteristic gas, carbon monoxide (CO) can be used for early detection of coal spontaneous combustion in mine goafs. Conventional gas analysis system for coal mine combustion monitoring is chromatography- based gas tubing bundles system, which suffers from long time delay. In this report, a sensitive and stable CO monitoring system was developed by using a distributed feedback (DFB) laser operating at 2.33 μm and a Herriott-type multi-pass gas cell with a 20-m optical length, taking advantage of the in-situ monitoring, excellent accuracy and simple structure available from direct absorption spectroscopy. The detection accuracy of system was about ±0. 2 ppm when as low as 1 ppm CO gas was detected. And data monitored can be used to determine that the detection limit of system was about 0.2 ppm. Further, a long-term continuous monitoring evaluation has clearly demonstrated the long-term stability and reliability of the monitoring system. The results obtained have validated the potential use of such a CO monitoring system in a practical monitoring application, such as the coal spontaneous combustion monitoring.