Research progress on coal mine laser methane sensor

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

Application and research of wireless laser methane sensor in drainage pipeline monitoring

Laser methane sensor has been widely promoted and successfully applied in coal mines as a new and effective technology building on the approach of laser-based absorption detection. Compared with the traditional catalytic methane sensor, the laser methane sensor discussed offers the important advantages of a long calibration period, high detection precision, the absence of zero drift and low power consumption, all of which are significant advantages for use in coal mining applications. By compensating for the temperature and pressure of the gases present, the accuracy of the methane sensor is evident across a wide range of temperatures and pressures, making it suitable for gas detection, including methane, in pipelines as well. The wireless laser approach which is incorporated into the methane sensor allows wireless transmission and data uploading to a cloud server through NB-IoT. This tackles the problem in gas pipeline monitoring of the length of many pipelines and thus the wide distribution of the sensors, avoiding complicated wiring and thus high associated cost. Further, remote data management can then be achieved, all of which greatly improves the flexibility and security of the management of the pipeline and the data generated

Gas cells for tunable diode laser absorption spectroscopy employing optical diffusers. Part 1: single and dual pass cells

New designs for gas cells are presented that incorporate transmissive or reflective optical diffusers. These components offer simple alignment and can disrupt the formation of optical etalons. We analyse the performance-limiting effects in these cells of random laser speckle (both objective and subjective speckle), interferometric speckle and self-mixing interference, and show how designs can be optimised. A simple, single pass transmissive gas cell has been studied using wavelength modulation spectroscopy to measure methane at 1651 nm. We have demonstrated a short-term noise equivalent absorbance (NEA, 1 sigma) of 2x10(-5), but longer term drift of up to 3x10(-4) over 22 hours

Development of Photonic Crystal Fiber Based Gas/ Chemical Sensors

The development of highly-sensitive and miniaturized sensors that capable of real-time analytes detection is highly desirable. Nowadays, toxic or colorless gas detection, air pollution monitoring, harmful chemical, pressure, strain, humidity, and temperature sensors based on photonic crystal fiber (PCF) are increasing rapidly due to its compact structure, fast response and efficient light controlling capabilities. The propagating light through the PCF can be controlled by varying the structural parameters and core-cladding materials, as a result, evanescent field can be enhanced significantly which is the main component of the PCF based gas/chemical sensors. The aim of this chapter is to (1) describe the principle operation of PCF based gas/ chemical sensors, (2) discuss the important PCF properties for optical sensors, (3) extensively discuss the different types of microstructured optical fiber based gas/ chemical sensors, (4) study the effects of different core-cladding shapes, and fiber background materials on sensing performance, and (5) highlight the main challenges of PCF based gas/ chemical sensors and possible solutions

Coal mine low power laser methane detection and alarm instrument

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

Water quality monitor

The preprototype water quality monitor (WQM) subsystem was designed based on a breadboard monitor for pH, specific conductance, and total organic carbon (TOC). The breadboard equipment demonstrated the feasibility of continuous on-line analysis of potable water for a spacecraft. The WQM subsystem incorporated these breadboard features and, in addition, measures ammonia and includes a failure detection system. The sample, reagent, and standard solutions are delivered to the WQM sensing manifold where chemical operations and measurements are performed using flow through sensors for conductance, pH, TOC, and NH3. Fault monitoring flow detection is also accomplished in this manifold assembly. The WQM is designed to operate automatically using a hardwired electronic controller. In addition, automatic shutdown is incorporated which is keyed to four flow sensors strategically located within the fluid system

Upgrading and testing program for narrow band high resolution planetary IR imaging spectrometer

An imaging spectrometer, intended primarily for observations of the outer planets, which utilizes an acoustically tuned optical filter (ATOF) and a charge coupled device (CCD) television camera was modified to improve spatial resolution and sensitivity. The upgraded instrument was a spatial resolving power of approximately 1 arc second, as defined by an f/7 beam at the CCD position and it has this resolution over the 50 arc second field of view. Less vignetting occurs and sensitivity is four times greater. The spectral resolution of 15 A over the wavelength interval 6500 A - 11,000 A is unchanged. Mechanical utility has been increased by the use of a honeycomb optical table, mechanically rigid yet adjustable optical component mounts, and a camera focus translation stage. The upgraded instrument was used to observe Venus and Saturn

Waveguide Mach-Zehnder interferometer for measurement of methane dissolved in water

In this dissertation, we present the development of a novel, compact and highly sensitive waveguide Mach-Zehnder interferometer to measure methane dissolved in water. Methane is a greenhouse gas, like carbon dioxide, and is emitted from both natural sources and human activities. Due to the challenges to measure dissolved methane in the sea and the vast area it covers, much of the methane cycle is unknown. In the last couple of years, there has been an up-swing in the development of subsea methane sensors. These high-end sensors rely on successfully separating the dissolved gas from the water with a membrane before the measurements, effecting the limit of detection, response time and it may give rise to hysteresis effects. Alternatively, samples can be transported to an on-shore laboratory, which can be time-consuming and expensive. We developed a methane sensor with the possibilities of direct and in-situ detection of methane with a relatively cheap and compact optical sensor-chip. A methane sensitive layer, consisting of a host-polymer and cryptophane-A, is deposited onto the chip. Cryptophane-A is a supra-molecular compound that can entrap methane molecules within its structure and thus, induce a change in the refractive index of the host-polymer. This change is detected by the evanescent field from the waveguide, in the sensing arm of the interferometer. Thus, with a change in refractive index in the sensitive layer, a phase change between the reference and the sensing arms of the interferometer is obtained. For obtaining optimal design, simulations were made for shallow silicon nitride rib waveguides with respect to the sensitivity as function of refractive index and the mode-behaviour of the waveguide. Once the design had been established, the waveguides were fabricated externally, with a core thickness of 150 nm, a rib height of 5 nm, rib widths of 1.5, 2 and 3 μm and sensing lengths of 1, 2 and 3 cm. The propagation losses were measured and simulated for tantalum pentoxide (similar to silicon nitride) strip and rib waveguides, to find the dependence of the propagation losses on the waveguide width. The sensitivity of the sensor was characterised with a diluted acid (HCl) and, in a separate measurement, by changing the temperature of the sensor coated with a polymer (PDMS). The sensor was combined with a methane sensitive layer of styrene acrylonitrile (SAN) and cryptophane-A, to detect methane gas. The sensitive layer showed a 17-folded sensitivity increase with a cryptophane-A to SAN ratio of 1:9. Methane gas was measured in the range of 300 ppm to 4.4%(v/v), with a detection limit of 17 ppm. Finally, the sensor was tested with methane in water. It was found that when the sensitive layer was exposed to water, the SAN polymer showed fractures along the surface. In an effort to circumvent the problem, a protecting layer of PDMS was deposited directly onto the SAN layer. However, after some time bubble structures appeared within the layer after exposure to water. Despite this, dissolved methane was successfully and repeatedly detected for concentration in range 9 to 46 μM. A detection limit of 49 nM was obtained, showing that the sensor is suitable for measurements of methane dissolved in water

Quantitative measurement of combustion gases in harsh environments using NDIR spectroscopy

The global climate change calls for a more environmental friendly use of energy and has led to stricter limits and regulations for the emissions of various greenhouse gases. Consequently, there is nowadays an increasing need for the detection of exhaust and natural gases. This need leads to an ever-growing market for gas sensors, which, at the moment, is dominated by chemical sensors. Yet, the increasing demands to also measure under harsh environmental conditions pave the way for non-invasive measurements and thus to optical detection techniques. Here, we present the development of a non-dispersive infrared absorption spectroscopy (NDIR) method for application to optical detection systems operating under harsh environments.Comment: 10 pages, 8 figure

Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation

We present a four beam ratiometric setup for an integrating sphere based gas cell, which can correct for changes in pathlength due to sphere wall contamination. This allows for the gas absorption coefficient to be determined continuously without needing to recalibrate the setup. We demonstrate the technique experimentally, measuring methane gas at 1651nm. For example, contamination covering 1.2% of the sphere wall resulted in an uncompensated error in gas absorption coefficient of ≈41%. With the ratiometric scheme, this error was reduced to ≈2%. Potential limitations of the technique, due to subsequent deviations from mathematical assumptions are discussed, including severe sphere window contamination