Research On Optical Fiber Methane Gas Sensor And The Measurement System Using LED As The Light Source

Optical fiber gas sensing technology is a developing and novel technique,which has a wide applicable prospect in industrial production, environmentmonitoring and medical science. In recent years, with the development ofoptical fiber sensing technology, the research of optical fiber gas sensor hasbeen seriously regarded all over the world. The signal detected by optical fibergas sensors is carried by light wave, which has no influence on the measuredobject. The sensor that has good independence performance itself can beadapted to all kinds of surroundings. The optical fiber sensing system with thesensors, which can be connected with computers conveniently, can realizemany functions request and intellectualized need. They can match with remotemeasure technology to measure and control in long distance.In this paper, methane is used as a research sample. The paper designs anall optical-fiber gas monitor system based on near-infrared absorption spectrummethod. The system can be used in real-time measurement of the methane gas.With analyzing and comparing with many gas measure methods andaccording to the system's need of measure precision and work condition, weselect spectrum absorption method as the theoretical way of this system. Afterstudying near-infrared selectivity absorption theory of the gas and methaneabsorption spectrum in near-infrared field, considering the attenuationcharacteristic of the transport optic fiber, the strong absorption spectrum ofmethane gas is confirmed. Using LED as the light source based on the theoryof wide source difference absorption measurement,being combined with aweak signal measure circuit with the core of lock-in amplifier and the circuit ofcomputer's control, the system is achieved to measure the concentration.Using the instrument and the condition of laboratory, the experiment ofthe designed system is carried out. They are composed of the sensitivity andresolving power of this system and the calibration of the whole system. Theexperimental results confirm the feasibility of the measure system.