Double-channel sensor for high precision measurement of methane-based on a dual-path Herriott cell

A double-channel methane (CH4) sensor was developed using a dual-pass multipass cell (DP-MPC) and a novel method that combines average dual-channel concentration signals with optimized detector gain configuration. This DP-MPC features two input/output coupling holes, resulting in absorption path lengths of approximately 95.8 meters and 35.8 meters, respectively. By optimizing the photodetector gain configuration and averaging the dual-channel concentration signals, the detection performance of the sensor was further enhanced. Allan deviation analysis indicated that under the 1-s integral time measurement precision of the sensor improved to approximately 20 ppb at a concentration of 2 ppm CH4 after dual-channel averaging and detector gain optimization. Meanwhile, the measurement precision improved by 2-3 times under the 10-s integral time. The sensor demonstrated its stability and reliability through continuous outdoor atmospheric CH4 measurements.