1、英文原文Effects of pressure and temperature fluctuations on near-infrared measurements of methane in underground coal minesJ. Shemshad ，AminossadatiW.P，BowenM.S. KizilAbstract: This paper presents the findings of an investigation into the effects of pressure and temperature variations on methane concent
2、rations measurements in near-infrared spectrum. The pressure and temperaturevariations that are expected in underground coal mines were found to have negligible effects on the uncertainty of spectroscopic measurement of methane concentration.1. IntroductionUnderground coal mines require accurate, fa
3、st, safe, and reliable real-time methane-measur- ement systems to monitorthe mine atmosphere. Methane detection systems are essential for the management of risks including gas explosions, spontaneous combustion, and underground fires as well as monitoring greenhouse gases. The mining industry curren
4、tly employs a range of meth- anemethane sensing systems including tubebundle systems. Measuring methane concentration in situ by infrared absorption provides more accurate and rapid results. Another method is by prop- agation of the infrared radiation through optical fibre to the surface for analysi
5、s. It is cheaper and more flexible to transmit electrical or optical signals over long distances than to transport gas sa- mples. Legal electrical safety requirements in underground coal mines make optical fibre syste- ms favourable. Optical fibre allows laser energy to be propagated over several ki
6、lometers and pr- ovides significant benefits such as low cost, fast response, and immunity to electrical interferenc- e.One of the challenges of underground methane sensing using an optical fibre system is sens- itivity of measurements to fluctuations in environmental conditions. This study quantifi
7、es the un- certainty of infrared methane concentration measurements due to typical pressure and temperatu- re fluctuations of underground coal mines.2. Overview of diode laser spectroscopyMany species of molecules have characteristic infrared absorption spectra which generate a fingerprint allowing
8、identificationof the molecules. This fingerprint can be detected by scanning an infrared laser over the absorption spectra. The laser intensity is absorbed by the gas molecules at resonance frequencies. Intensity analysis of the transmitted laser light allows the gas species to be identified. The co
9、ncentration of the gas can also be determined from the level of absorption n-ear resonance, with the transmitted intensity given by the BeerLambert Law 1, 2: (1)where It and I0 are the transmitted and incident light intensities at frequency of (cm1), respect- tively. k (cm1) is the spectral absorpti
10、on coefficient and L (cm) is the path length of the light th- rough the gas (Fig. 1). Fig. 1 Laser light through a gas speciesThe spectral absorption coefficient，kv (cm1), is defined by (2)where j is the number of transitions, Si(T ) (cm-2 atm-1) is the line intensity of the transition i at temperat
11、ure T , (cm) is the line-shape function for transition i , and is the full width at half maximum (FWHM) of the absorption line. N is the number density of molecules in the gas and can be determined using the ideal gas law： (3)where k is the Boltzmann constant, C is the concentration, P is the pressu
12、re, and T is the temper- ature of the gas. The transitions with a line-shape function of （cm）are broadened by using Voigt broadening 35 in the case of both temperature and pressure effects. The Voigt pro- file is given by (4)where V (a,b) is the Voigt function: (5)In the above equations, andare the
13、Doppler and Lorentzian line widths respectively, a- nd are given by (6) (7)where 0 (cm-1) is the line-centre frequency，T (K) is the absolute temperature, M is the molecul- ar weight of the gas species, P (atm) is the pressure of absorbing species, is the mole fraction of the component of the gas mix
14、ture, is the pressure broadening coefficient at a reference te- mperature of T0, and is the species dependent temperature coefficient.3. Wavelength modulation spectroscopy and harmonic detectionWavelength Modulation Spectroscopy (WMS) 613 involves sinusoidal modulation of the laser wavelength of a f
15、requency much smaller than the line width. The response is mainly detected at first and second harmonic signals. As the response is proportional to the derivative of the absorb- ance, the technique is referred to as the derivative spectroscopy. For a known optical absorption path length and weak modulation, the second harmonic signal is related to the second Derivative of the absorbance, and can be used to infer the species concentration.The laser wavelength output is modulated by a sine w
