Study On Optical Fiber Methane Sensor Technology

In latest years, damp accidents happen frequently. The fire or explosioncaused by damp has been a serious threat to people’s life and property safety.The damp is mainly methane gas, so the development of a methane sensorwith high accuracy and fast response speed has become a urgent need.By the analysis and comparison with traditional electric gas sensor, thispaper expounds the advantages of optical fiber gas sensor, and finally pointsout that the gas sensor with infrared spectral absorption is one of the mostpromising sensing scheme. It is based on the theory of Lambert-Beer law, andwith the advantages of simple structure, good practicability and so on.Because of this it is to occupy the mainstream gradually.Early studies on the absorptive fiber gas sensor mainly use the directdemodulation on the strength. The equipment with this technique is easilyinfluenced by environment, light source and the power fluctuation of thedetection circuit, while the technology of harmonic detection is justintroduced to completely solve this problem. Harmonic detection is often used in nuclear magnetic resonance, Zeeman and Stark spectrum analysis that needto extract weak signal from strong background. This paper introduces atunable diode laser absorption spectroscopy (Tunable Diode LaserAbsorption Spectrum, TDLAS) which is composed of the technology ofdistributed feedback semiconductor laser (Distributed Feedback, DFB)wavelength tuning and harmonic detection.By many experiments, the paper analyses the effect of the wavelengthtuning and "power-current" characteristics of DFB in practical application.Combined with harmonic detection technology, It uses the infrared absorptionspectrum of methane gas to design a kind of methane absorption spectrumfiber gas sensor system. The experimental data prove that it is a kind of highaccuracy, high sensitivity methane gas sensing scheme. It has the advantagesof simple structure, low cost, strong anti-interference ability, convenientcarrying, high selectivity to gas molecules. It adopts the distributed feedbacksemiconductor laser (Distributed Feedback, DFB) as light source, uses thelock-in amplifier circuit in harmonic analysis and a compensation method in the gas concentration demodulation with the first-order modulation frequency.