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With the advances in clean energy, natural gas (methane) takes a greater proportion in total energy consumption. Methane gas detection technology has become an important research direction for fire alarm area. Using near-infrared absorption spectroscopy method, this gas detection technology has many unique advantages, such as intrinsic safe, good stability, good selectivity, long working life, etc. In this paper, a gas detection system based on wavelength modulation and second harmonic (2f) signal detection technology is proposed; the process of the first and second harmonic demodulation is simulated; the feasibility of using first harmonic as light intensity reference and the linear relationship between the concentration and second harmonic is analyzed. Finally, a theoretical guidance for product developing with above technology is provided as well.

The paper discussed mainly two aspects when testing detection performances of detectors for flammable gases, measuring principle of sensors and application environment of detectors. For different kinds of sensors, the performance characteristics decide immunity from interference of temperature and other gas, and according to application field, some special tests, for example, EMC tests are necessary. And provided a clear thinking to combine design of tests with practical application of products, which made the detectors meet the needs of practical application. It also put forward some conceptions for future development of testing technology.

Apart from using fire retardant materials, fire detection and alarm system could be another effective way to improve overall fire safety level of rail vehicles. And this has been suggested by the latest European Standard. However, in China, such application has not been well studied or standardized yet. Therefore, in this paper, by a study into major foreign standards and relating literatures, the author summarizes some major considerations for standardization of using fire detector in rail vehicles. And some suggestions as well as future work are proposed for establishing such standard in China.