A compact dual-gas sensor based on the two near-infrared distributed feedback diode lasers and a multipass cell has been established for the simultaneous measurement of methane (CH4) and acetylene (C2H2). The time division multiplexing calibration-free direct absorption spectroscopy is used to eliminate the cross interference in the application of multicomponent gas sensors. A wavelength stabilization technique based on the proportion integration differentiation feedback control is developed to suppress laser wavelength drift and an H-infinity (H∞) filter algorithm to reduce the system noise. The results show that the detection sensitivity of CH4 and C2H2 reaches 39.9 parts per billion (ppb) and 47.3 ppb in the optimal integration time of 556 s and 312 s, respectively. In addition, the 31 consecutive hours measured results of CH4 in outdoor ambient air show that the proposed detection technology is very suitable for high-precision in-situ measurement of trace gases.
Keywords: H-infinity; PID control; TDLAS; Tunable diode laser absorption spectroscopy; dual-gas sensor; proportion integration differentiation control; trace gas detection.