Aiming at disadvantages of large size and close detection distance of previous methane measurement systems

propose a methed and circuit design using distributed feedback laser（ DFB） for safety detection of gas pipeline. Focusing on design of orthogonal digital phase-locked amplifier based on field programmable gate array（ FPGA） and improved design of distributed feedback laser drive circuit and temperature control circuit

theoretical research and experimental verification on FPGA core control circuit

laser drive circuit and temperature control circuit are conducted. The ratio of first harmonic and second harmonic is used to calculate the gas concentration in the laser path. The experimental results show that the minimum detecting concentration of the system reaches 20 × 10-6

and the detecting distance can reach 40 m

and the long-distance and high-precision detection requirements of the system are met.