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.
Laser ultrasonic technology has become an effective method and technological means for thickness measurement of metal materials nowadays. Generally, common method for receiving laser ultrasonic signals has piezo-electric transducer (PZT), laser interferometer and electro-magnetic acoustic transducer (EMAT). In this paper, the receiving principles of three kinds of receiving methods are given, and the diagrams of three methods with different thickness obtained by experiments are drawn. Each method has its own advantages and disadvantages, so appropriate receiving method should be selected according to actual needs for engineering application.
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.
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.
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