The Uncertainty Evaluation of Determining the Trace H₂S in SF₆/N₂ Insulating Gas Mixture by Cavity Ring-Down Spectroscopy

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H 2 S is one of the most important characteristic components of sulfur hexafluoride gas insulated electrical equipment. The detection of trace H 2 S is of great significance for early fault diagnosis of such equipment. Based on the 1578 nm wavelength distributed feedback diode laser (DFB-DL), cavity ring-down spectroscopy (CRDS) can effectively measure the concentration of trace H 2 S in SF 6 /N 2 gas mixtures. Starting from the principle of methodology, this article establishes a mathematical model for evaluating the measurement uncertainty of CRDS and analyzes its sources of uncertainty: gas constant R 1 , temperature T , Avogadro constant N A , gas pressure p in the optical cavity, volume V of the optical cavity, speed c of light, the absorption cross-section parameter σ (ν) of H 2 S molecules in the laser frequency ν , the ring-down time τ with absorption sample H 2 S and the ring-down time τ 0 without absorption sample. After evaluating the uncertainty components, it was found that the main component was σ (ν) and the secondary components were τ and τ 0 . The H 2 S content in the 80% SF 6 -20% N 2 mixed gas measured is (7.64 ± 0.12) × 10 −6 mol/mol.