Design and characterization of long path absorption cell and digital lock-in amplifier for multi-channel infrared gas sensor

A high-precision three-gas detection system based on non-dispersive infrared (NDIR) technique was designed to accurately detect multiple gas concentrations in a complex environment. This system consists of an infrared source, a quad channel pyroelectric detector, a signal processing circuit and an optical gas chamber. A multiplexed digital lock-in amplification algorithm based on MCU was realized to improve accuracy, it has low cost of multiplex, there is potential to be applied to the measurement of multi-channel data. And a compact gas cell with the size of 40mmx 110mmx22mm was designed, in which the average optical path length is 475mm. Initial measurement was done to one channel for SF6 gas concentration, and the feasibility of gas cell structure and signal processing circuit was demonstrated.