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.
At present, the portable carrier catalytic methane detection and alarm instrument for coal mine generally has many problems, such as high power consumption, short standby time, low detection accuracy, few parameters and single function, which can not meet the rapid development needs of mine safety. In this paper, a low power portable laser methane detection and alarm instrument based on tunable laser absorption spectroscopy (TDLAS) is designed. The instrument can detect methane concentration, ambient temperature and ambient pressure at the same time. It has the functions of sound and light alarm, historical data storage and query, and integrates Wi-Fi to realize data wireless transmission. The instrument can work continuously for 36 hours, and the response time is less than 15 seconds. It has the function of self-diagnosis. The overall performance of the instrument has been greatly improved compared with the traditional mine methane portable instrument. A mobile methane alarm Internet of things(IOT) system for coal mine based on portable instrument has been developed, which realizes real-time upload of data and cloud analysis, makes the traditional mine gas monitoring and control system powerfully supplemented, greatly improves the detection level of coal mine gas, and has broad application prospects.
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.