Design And Development Of Long-distance And High-precision Laser Methane Telemetry System

In view of the gas pipe network in the industrial park,the gas tank area and the gas pipe line in the key area of the city,the gas combustible gas leakage caused by the aging,damage or construction negligence caused by the artificial damage of the pipeline will cause urban safety and personal safety and other problems,which must be paid attention to by the safety department and the public.Therefore,it is of great significance to carry out all-weather and automatic inspection for the security status of relevant areas.Tunable Diode Laser Absorption Spectroscopy-Wavelength Modulated Spectrum,Tunable diode laser absorption spectroscopy-wavelength modulated spectrum,The TDLAS-WMS telemetry system for methane（CH₄）leaks is designed to meet the requirements of high precision,non-contact and remote detection of CH₄ gas leaks.The absorption peak of CH₄ molecule at 6046.995 cm-1（1653.72 nm）was selected as the absorption spectrum line for CH₄ concentration detection.The central wavelength of the tunable distributed feedback（DFB）laser was stabilized around1653.72 nm by adjusting the temperature and modulating the drive current through TEC temperature control chip MAX8521.So that it can accurately absorb CH₄ molecules to form absorption spectral lines,and obtain effective information such as line intensity and line width.The system adopts the dual-core architecture of advanced reduced instruction set machine（ARM）and field programmable logic gate array（FPGA）.FPGA realizes digital phase-locked demodulation to extract the first harmonic（1f）and second harmonic（2f）signals.ARM receives 1f and 2f signals demodulated by FPGA in real time through SPI and sends them to Lab VIEW for harmonic signal analysis and online demodulation of methane concentration.In this study,2f/1f signal processing technology is used to eliminate the influence of the changes of light intensity and target reflection coefficient on the measurement results of the system,and the relationship between the harmonic signal and the detection distance in the range of 0 m～90 m under the same experimental conditions is analyzed.The results show that 2f/1f signal processing technology has a significant effect on noise suppression.At the same time,the harmonic signal of CH₄ gas in the range of 0 ppm·m～26000 ppm·m was measured to explore the relationship between the integral concentration of different CH₄ gas,and the linear interval of the system was studied.The least square method was used for linear fitting of 2f/1f and gas integral concentration data,and the calibration linearity of the system was 0.9966.The system error is measured and analyzed experimentally.The maximum relative error is-3.66%and the minimum is-0.23%in the range of 0 ppm·m～2000 ppm·m.The detection limit of the second harmonic signal evaluation system using 1500 ppm·m CH₄ integral concentration is 70.5 ppm·m.Taking the underground yellow gas pipeline network of Hefei Institute of Public Safety and Tsinghua University as the experimental platform,the distance of 7 m,15 m and 30 m is selected as the actual simulation distance,and the relative measurement error of the system is-0.87%,-2.32%and-5.24%,respectively.The results show that the designed and developed CH₄ leakage telemetry system can be widely used in the monitoring and warning of sudden gas leakage in urban gas station and natural gas pipe network.Figure[43]table[4]reference[89]...