Detection of characteristic component H2S in SF6 and SF6/N2 mixture using cavity ring-down spectroscopy

A high-sensitivity cavity ring-down spectroscopy gas detection system with integrated optical components and embedded microprocessor units is presented for the detection of hydrogen sulfide (H₂S) in sulphur hexafluoride (SF₆) and its mixture with nitrogen (N₂). The system exploits a periodic laser wavelength modulation to simplify the mode matching. Spectral line profile fitting is used for sample quantitative analysis. To verify the sensitivity and stability of concentration detection, the effect of background gas and temperature on the responses of spectral line broadening and absorption cross-section are investigated. The result deviation caused by variation of background gas can be compensated by the pre-correction of empty cavity ring-down time. It is also found that the implication of temperature on the spectra cannot be ignored. The full width at half maximum and peak value decreased linearly with the increase of temperature, while the baseline is undergoing accelerated growth. Using Allan variance analysis, the limits of detection reach 4.44 × 10⁻⁹ in SF₆ and 2.96 × 10⁻⁹ in N₂ with average time of 67 s. This study provides a meaningful approach for the online detection of characteristic gas in gas insulation equipment.