CH4/C2H6 dual-gas sensing system based on wavelength modulation spectroscopy using a single near infrared laser

For sensitive and accurate methane (CH4) and ethane (C2H6) simultaneous detection, a near-infrared dual-gas sensing system based on wavelength modulation spectroscopy (WMS) was developed. A fiber-coupled distributed feedback (DFB) diode laser emitting at 1.684 μm was employed as light source. The scanning and modulation signals applied to the injection current of the laser were designed based on time division multiplexing (TDM) to realize the dual-gas measurement. A White cell with absorption path length of 16 m was utilized. The light intensity signal detected was processed with python based digital quadrature lock-in amplifier to obtain first and second harmonic signals. Allan deviation analysis yielded detection limits of 23.53 ppb for CH4 and 146.4 ppb for C2H6 in an average time of 100 s.