| Methane monitoring is the most important part of safety monitoring and controlling in our country. The detection technologies of our country are mainly the traditional optical interference technique and thermal catalytic technology, but these technologies are badly impacted by the mining environmental, with low precision, poor reliability. So this paper studies a kind of gas measurement technology, and introduced a remote measurement system.The system uses a excellent technology named tunable diode laser absorption spectroscopy ( TDLAS ).We can measure the methane concentration of the changeful environment accurately and reliability by using the technology of laser absorption spectroscopy. Following the predecessor’s step in this field, we research on the relationship of gas concentration and the ratio of first harmonic signal and second harmonic signal, compared with the previous system, which has the shortcomings such as weakly signal and necessary gas chamber. Our concentration system overcomes the decay of laser intensity which caused by the background gas, dust and other factors.After analyzing the theoretical, we set the laser’s center wavelength at 1654nm, and the laser frequency is locked in the methane’s strong absorption band,the laser which reflected from the target transmits through the gas zone to the lens,and received by the system. We apply a detection method which can finally measure the concentration of methane gas by detecting the first harmonic and second harmonic of the reflected signals.The system use the ARM ( S3C2440A ) as the chief chip, and we also design the minimum system, and embedded the Linux system into the minimum system. We can detect signal by a lock-in amplifier, after the analog to digital conversion, we can use the digital to calculate the concentration of methane.After designing the software system, selecting the algorithm mode. We get the experimental data by the system simulation and measurement and analyze the effect factors. |
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