Abstract
A ppb-level CO sensor based on multi-comb optical-feedback cavity enhanced absorption spectroscopy with a 2.3 μm diode laser was developed for SF6 decomposition analysis in electric power system. The effective optical path reached to 4.5 km within 35 cm length cavity. Besides, through modulating the cavity length five times automatically, the spectral resolution was improved to 0.0015 cm−1 from 0.0071 cm−1. Targeting the R(6) line of CO first overtone band at 4285.01 cm−1, which is interference free from absorption spectra of SF6 mixtures (SF6, SO2, H2S, SO2F2, HF, CF4, CO2, COS, O2 and H2O), the minimum detection limit and detection precision under different gas pressures were performed. At optimum integration time of 30 s determined by Allan deviation analysis and gas pressure of 40 torr, the minimum detection limit and detection precision of CO were better than 18 ppb and 150 ppt, respectively.
Highlights
Trace gas sensors based on tunable diode laser absorption spectroscopy (TDLAS) are widely used due to their high detection sensitivity and selectivity as well as fast response time, which permits online monitoring of target gas concentrations[7,8,9,10]
Based on the test of pure SF6 (99.99%) by Fourier Transform Infrared (FTIR) spectrometer and simulation of SO2, H2S, SO2F2, HF, CF4, CO2, COS, O2 and H2O based on HITRAN database, R(6) transitions located at 4285.01 cm−1 in the first overtone band of CO was selected as the target detection absorption line, which is interference free from absorption spectra of SF6 mixtures
Over 50 ms, the laser locked to 29 successive cavity modes with a locking time of 510 μs estimated by the full width at half maximum (FWHM) of mode, much longer than the ring-down time, τ0
Summary
Fu Wan 1,2, Feng Zhou[1], Jin Hu1, Pinyi Wang[1], Jianxin Wang[1], Weigen Chen[1], Chengzhi Zhu3 & Ye Liu[3]. A ppb-level CO sensor was achieved by combined the TDLAS technique with a mid-IR laser targeting the strongest fundamental ro-vibrational transitions of CO, these CO sensors were developed to operate in an air or exhaled gases environment and may not adapt to detect trace CO in various fault characteristic gas mixtures because the cross interference from absorption of SF6, SO2, H2S, SO2F2, HF, CF4, CO2, COS, O2 and H2O (SF6 mixtures) cannot be ignored. A piezoactuator attached to the rear of an end mirror of V-shaped cavity is constructed to allow the cavity length to be carefully modulated and change the position of the comb of build-up modes, more data points per frequency unit and a high lineshape precision are achieved This optical sensor system realizes highly sensitive and precise analysis of SF6 decomposition component CO in SF6, SO2, H2S, SO2F2, HF, CF4, CO2, COS, O2 and H2O at the target absorption line of 4285.01 cm−1
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