Multicomponent gas detection technology of FDM and TDM based on photoacoustic spectroscopy

In this paper, a multicomponent gas detection system based on photoacoustic spectroscopy (PAS) is proposed with a combination of frequency division multiplexing (FDM) and time division multiplexing (TDM), combining a resonance photoacoustic cell and broadband microphone. A PAS gas cell with a wide frequency response bandwidth was used to achieve the FDM by selecting a specific modulation frequency of each component gas. The sawtooth wave driver current of each laser was output at a constant time interval for achieving the TDM. Compared with the laser channel control using a photoswitch, the driver current control was a simpler and more convenient means to implement TDM. The four gas components of methane ( C H 4 ), water ( H 2 O ) vapor, carbon dioxide ( C O 2 ), and acetylene ( C 2 H 2 ) were selected as sample gases for testing the feasibility of the method. The experimental results showed that the gas detection limits of C H 4 , H 2 O vapor, C O 2 , and C 2 H 2 were 75.435, 2.502, 341.960, and 4.284 ppm, respectively. In addition, the linear fittings of gas concentration were 0.99386, 0.99772, 0.98995, and 0.98955, respectively.