Development of fiber Bragg grating underground gas flow sensor

Abstract

Coal mines have abundant coal seam gas reserves underground, and disasters such as coal and gas outbursts and gas explosions occur from time to time. The key work to reduce coal mining safety accidents is to use the “first pumping, then mining” method to control coal mine gas. A gas extraction flow measurement sensor was developed using fiber Bragg grating (FBG) and an orifice plate. In response to the environmental conditions and flow range of underground gas extraction, a composite strain mechanism consisting of a small-diameter throttling orifice plate and an elastic sensitive membrane was adopted. The gas flow pressure difference on both sides of the orifice plate caused deformation in the elastic sensitive unit, and the fiber Bragg grating was used to detect the deformation of the elastic sensitive unit; A dual membrane structure gas flow sensor is proposed to address the stress–temperature cross sensitivity issue in fiber optic grating strain detection. Based on the mechanical free state configuration, a secondary grating is attached to the same material as the strain grating for temperature compensation, effectively eliminating the cross sensitivity problem of the grating and improving the measurement accuracy of the sensor. The experimental results show that the nonlinear error is 1.57%, the hysteresis coefficient is 3.14%, and the repeatability error is 8.3%. The experimental results fit well with the theoretical analysis.