Fiber-optic photoacoustic sensor with SF6 purity correction for decomposition derivative H2S based on 1f and 2f dual-modes

A single fiber-optic photoacoustic sensor (FOPAS) is applied for the simultaneous detection of the SF6 purity and decomposition derivative H2S, and the photoacoustic measurement results are corrected based on the SF6 purity. SF6 purity and H2S gas concentration are identified by tracking frequency and detecting photoacoustic signal based on 1f and 2f, respectively. The influence of SF6 purity on the resonance frequency, photoacoustic excitation intensity, and cantilever frequency response are theoretically derived, simulated, and experimentally verified. In the range of 80%–100%, there is a linear relationship between the resonance frequency and the SF6 purity, with a response of 1.923 Hz/% and a minimum purity change detection limit of 0.02%.The FOPAS based on the designed T-type photoacoustic cell achieves a detection limit of 5 ppb for H2S, and the normalized noise equivalent absorption coefficient of the FOPAS reaches 4 × 10−10 cm−1 Hz−1/2 W. Taking SF6 purity of 97% as an example, the frequency response of FOPAS and the photoacoustic signal are evaluated both before and after correction. By correcting the resonance frequency and photoacoustic signal, the detection accuracy of H2S gas is improved by 9%. By adopting the SF6 purity and decomposition derivative overall analysis method, simultaneous high-precision and high-sensitivity monitoring of dual-state parameters has been achieved, providing technical support for accurate early warning of latent faults in SF6 gas-insulation equipment.