An optical fiber remote methane gas on-line monitoring system

摘要

We report on a fiber optic infrared methane gas detection system,which is based on distributed feedback (DFB) laser diode at around 1665 nm.The gas sensor is made of normal telecommunication fiber,signal also transmitted via fiber link,hence free of electricity and intrinsically safe.The system is capable of self-referencing of the absorption line and self-correction of the intensity fluctuation.It can be used for remote monitoring over 10 km range.The injection current of the DFB laser diode is modulated with a saw-tooth wave to provide wavelength scanning across a methane absorption line at around 1665 nm.The methane gas sensor has been designed to minimize the effect of dust,moisture and vibration.It is constructed with fiber pigtailed graded index (GRIN) lenses and operating in reflection mode for convenient access.This instrument is currently undergoing site trials in a coal mine in Shandong province,China.Long term accuracy of 0.05% has been achieved.This new remote online methane monitoring system exhibits significant potential for coal mine methane gas monitoring in the future.