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, such as the slope of normalized baseline restricted the sensitivity and accuracy, the effect of cross-talking interferences becomes a technical bottleneck for multi-gas detection. Therefore, a high sensitive synchronous detection technology for multi-gas detection using the multiple linear regression analysis method is reported. The wavenumber of 4291cm-1 has been selected to detect CO and CH4. Several characteristic points are selected to establish multiple linear regression equations, then the concentrations of CH4 and CO can be calculated, and the baseline can also be obtained simultaneously. The Allan variance results indicate that the optimal integration time has been improved to ~60s, the minimum measurement precision of CH4 and CO is ~0.58% and ~0.41×10-6 respectively. Meanwhile, the detection cost and response time can be reduced obviously
ABSTRACT The continuous emission of greenhouse gases leads to the sharp rise of environmental temperature. Its content and distribution also affect the atmosphere radiation, climate characteristics, stratosphere troposphere exchange (STE) and circulation in the near-tropopause region. Methane is the second most important greenhouse gas after carbon dioxide, and its concentration has strong gradients near the tropopause. Therefore, the sensitivity, accuracy of methane detection approach in extreme environment have been greatly restricted, and this has become a technical bottleneck for low-temperature and low-pressure gas detection. To address this, a novel 3-dimensional compensation model of temperature and pressure is reported based on the simulation of methane absorption characteristic. Through a detailed investigation, the simulation system and compensation model are evaluated, the detection accuracy is improved by an order of magnitude; the minimum detection limit is ~0.012ppm with integration time is 59s.
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.
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.
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.
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.
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.
Because of its special structure, photonic crystal fiber(PCF) has shown great potential in gas sensing. Probe beam with the test gas can directly interact within a PCF. PCF gas sensor with a very small amount of gas can be interact with light in optical fiber in a long distance. And you can change the parameters of the fibers can be improved sensor sensitivity, etc. The status of solid core PCF and hollow-core PCF as a gas sensor is introduced respectively in this paper.
Based on the technology of the spectrum absorption and the FBG, the monitoring system realize on line detection of the concentration of methane and oxygen, the temperature and the pressure of the gas in pipeline, and in order to improve the accuracy of the gas detection, we induce the compensation to the gas concentration using the data of the temperature and the pressure. In order to have a effective utilization of the methane in the coal mine gas drainage system, we have to have a accurate measurements of the concentration, the temperature and the pressure of the gas in pipeline. At the same time the dynamic monitoring of the concentration of Oxygen is a sign of the leakage of the pump. This paper gave some data detected in the field of the coal mine gas drainage system.
This paper describes an optical fiber oxygen sensor based on wavelength scanning and spectrum absorption technique. An open path optical gas chamber is employed to analyze the absorption lines of oxygen in visible region. The oxygen sensor works in the concentration range 0-100% oxygen with good performance in stability and sensitivity. The precious is less 0.5% over 30 hours in atmosphere. The results show that it will have a great potential application in the harsh environments.
Carbon monoxide is one of the important gases need to be detected in coal mine safety. Detection technology based on signature gas is the primary means of spontaneous combustion forecasting of coal goaf area. Because of the high accuracy requirement of CO concentration in the coal mining applications, we had to introduce more data processig methods to improve the signal-to-noise ratio (SNR), finally to achieve the requirements of coal mining. Therefore, we used three data processing methods to eliminate noises of the CO sensing system which based on the tunable diode laser absorption spectroscopy (TDLAS): Fourier transform, least-squares fitting and Kalman filter. The results show that the combination of three data processing methods had a good inhibitory effect of random noise and interference fringes, etc. and significantly improved the system detection accuracy, the minimum detectable spectral absorption rate could be increased by an order of magnitude. So this high-resolution fiber CO sensing system can better meet the needs of coal mine safety.
Coal mine belt transport system is the most important transportation system, directly determines the normal operation of coal mine production safety, so it is necessary to secure real-time online monitoring of running status. Based on distributed optical fiber temperature measurement technology, developed a coal mine belt conveyor running state online monitoring system, achieved to monitor the Real-time temperature of mainly electromechanical device and all the belt line. Field data analysis showed that coal mine belt conveyor state on-line monitoring system of based on DTS can real-time accurately monitor the temperature and belt conveyor running state, to guarantee the coal belt conveyor safe operation and offer a strong support.for the realization of the state maintenance of equipment.
Spontaneous combustion in coal goaf area is one of major disasters in coal mines. Detection technology based on
signature Gas is the primary means of spontaneous combustion forecasting of coal goaf area. A real-time remote fire gas
detection system is proposed based on tunable diode laser absorption spectroscopy technology, to achieve valid test of
Carbon Monoxide signature gas. The System uses the wavelength, respectively 1.567um near-infrared band fibercoupled
distributed feedback laser (DFB) as the light source, combined wavelength modulation spectroscopy and
harmonic detection technique, developed a fiber-coupled white-type long-path gas absorption cell, to achieve high
sensitivity detection of gas concentration. The system achieved a remote on-line monitoring of Carbon Monoxide gas
concentration, to meet the fire forecast need for Coal Mine goaf area.
Carbon dioxide is one of the important gas need to be detected in coal mine safety. In the mine limited ventilation
environment, Concentration of carbon dioxide directly affects the health of coal miners. Carbon dioxide is also one of
important signature Gas in spontaneous combustion forecasting of coal goaf area, it is important to accurately detect
concentration of carbon dioxide in coal goaf area. This paper proposed a fiber carbon dioxide online sensing system
based on tunable diode laser spectroscopy. The system used laser absorption spectroscopy and optical fiber sensors
combined, and a near-infrared wavelength 1608nm fiber-coupled distributed feedback laser (DFB) as a light source and a
7cm length gas cell, to achieve a high sensitivity concentration detection of carbon dioxide gas. The technical
specifications of sensing system can basically meet the need of mine safety.
Tunable diode laser absorption spectroscopy (TDLAS) based optical fiber methane sensing technology has a
number of advantages compared with conventional electronic methane sensor device, such as high Precision, passive and
intrinsically safe in explosive and hazardous environment as well as immune to electro-magnetic interference. In order to
accurately measure the oxidation rate of coal mine ventilation air methane oxidizer system, and Meet requirements for
accurate measurements to the oxidizer exhaust emissions, A Fiber optic methane monitor based on Distributed feedback
tunable diode (DFB) laser of 1.65um central wavelength is demonstrated. We use a reflective chamber of only a 10cm
effective optical path as sensing gas cell. By the data processing of fitting baseline method, we remove the effect of the
baseline tilt of background Spectral. The system achieves 0 to 0.1% measure range and 5.8*10E-6 minimum detection
sensitivity, and meets the requirements of high accuracy, real-time measure to the oxidizer exhaust emissions.
Spontaneous combustion in coal goaf area is one of major disasters in coal mines. Detection technology based on
signature Gas is the primary means of spontaneous combustion forecasting of coal goaf area. A real-time remote fire gas
detection system is proposed based on tunable diode laser absorption spectroscopy technology, to achieve valid test of
signature gas (CO, CO2, CH4, C2H2 and C2H4). The System uses the wavelength, respectively 1.567um, 1.608um,
1.653um, 1.530um, 1.623um near-infrared band fiber-coupled distributed feedback laser (DFB) as the light source,
Combined wavelength modulation spectroscopy and harmonic detection technique, developed a fiber-coupled white-type
long-path gas absorption cell, to achieve high sensitivity detection of gas concentration. The system achieved a remote
on-line monitoring of multi-component gas concentration,to meet the fire forecast need for Coal goaf area. There are
obvious advantages Compared with the existing beam tube monitoring system in coal mine.
Fiber optic methane monitor based tunable diode laser absorption spectroscope technology (TDLAS) is
demonstrated, which is developed for remotely monitoring the concentration of Methane gas at multiple locations. A
DFB LD light source of 1665nm is the key unit in the system.A microprocessor is used to control the driver of DFB LD
and Acquire data.To realize high precision measure of CH4,we use a reference cell. The instrument achived long time
precision of 0.05%(for 0~4% full scale range) and 0.5%(for 0~100% full scale range).The instruments has been used to
monitor the mathane of a VAM Oxidiser unit in methane power generation in a long time .The results of measurement
are shown and discussed in this paper.
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