Spectrum Absorption Methane Gas Sensor with Optical Fiber Based on Frequency Harmonic Detection Mechanism

Abstract

Methane is an easily burning and exploding gas. It is the primary component of many gas fuels such as mine gas and natural gas and so on. In the coal mine accidences of our country, the casualties caused by gas explosion covers over 50% in all great casualties, and it becomes the largest obstruction of safe production. Incident online detecting methane gas density has important significance for mine and plant safe production and personal safety. Based on the near infrared spectral absorption of methane, a system using absorption type optical fiber for high sensitivity methane detection is demonstrated in this paper. DFB LD is adopted as light source in this paper. Modulating the light source, methane gas is detected by second harmonic. The ratio of the fundamental and second harmonic signal can be used for eliminating the interference owing to light power changing. The mathematical model of gas concentration harmonic measurement is built up. The result of methane concentration is also shown. The system overcomes the defect of great interference of available instruments by light route. It has advantages such as high sensitivity, quick response speed, large dynamic range, preventing electromagnetic interference, preventing burning and explosion, not easily being poisoned and so on. The probe can be put in condition of easily burning and exploding, being poisonous being high temperature and so on that man and instrument can not easily enter. It can realize online continuous telecontrol and telemeter.

Environmental Application of High Sensitive Gas Sensors with Tunable Diode Laser Absorption Spectroscopy

“…For gas mixing ratio detection, WMS is often adopted. The intensity of 2f signal can be expressed as [40] I 2f ∝ I 0 σ 0 CL…”

Gas detection techniques with fiber optical spectrum absorption at near-IR wavelength

“…The second-harmonic intensity variation inherent in the laser beam, resulting in a signal offset, is eliminated beforehand by modulation waveform correction. Two detection schemes, the transmission scheme as shown in figure 1 technique is used to detect the concentration of methane [15][16] [17] . With gas cell length of cm 0 5 , the sensitivity of detected concentration is ppm 0 1 , which is only 0.02% of the lower explosive limit of methane.…”

A Gas Monitoring and Control System in a Coal and Gas Outburst Laboratory

“…On preparing the experiments, in case of a gas leak the general method used is to install gas sensor probes mounted in the laboratory such as fiber methane gas sensors to monitor the gas concentration. When the gas leak achieves the prethreshold, the alarm system is activated [13][14][15][16]. But a simple method of monitoring could bring the first challenge: (1) the discontinuity of work because of a gas leak: after the beginning of the experiment, the general protective measure used is to keep the staff far away from the experimental devices until the gas totally disappears, which may even take several days, which can be considered as the second challenge; that is, (2) lower experimental efficiency induced by the lack of a powerful gas discharge system: more importantly, the results from the minioutburst experiments are always reported in format of the quantity and distribution of coal in a gas outburst under altered conditions by changing the gas pressure, coal power sizes, and outside loads; the third challenge (3), the role of gas spread, is rarely reported as a result of the lack of gas monitoring systems for collecting the gas concentration trend, which limits the value of miniexperiments.…”