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We designed and implemented a photoacoustic (PA) sensor for H 2 S detection in SF 6 background gas based on a multi-pass differential photoacoustic cell (MDPC) and a near-infrared distributed feedback (DFB) laser. In the MDPC apparatus, two resonators with identical geometric parameters were vertically and symmetrically embedded. The differential processing algorithm of two phase-reversed signals realized the effective enhancement of the PA signal and suppressed the flow noise in the dynamic sampling process. In addition, the λ/4 buffer chamber in the MDPC was utilized as a muffler to further reduce the flow noise and realize the dynamic detection of H 2 S. The collimated excitation light was reflected 30 times in a multi-pass structure constituted of two gold-plated concave mirrors, and an absorption path length of 4.92 m was achieved. Due to the high gas density of SF 6 , the relationship between the signal-to-noise ratio (SNR) and the gas flow was different between SF 6 and N 2 background gases. The maximum flow rate of the characteristic gas components detected in the SF 6 background is 150 standard cubic centimeters per minute (SCCM), which is lower than 350 SCCM in N 2 . The linearity property was analyzed, and the results show that the sensitivity of the sensor to H 2 S in the SF 6 background was 27.3 μV/ppm. With the structure, parameters, temperature, gas flow, and natural frequency of the MDPC been optimized, a minimum detection limit (MDL) of 11 ppb was reached with an averaging time of 1000 s, which furnished an effective preventive implement for the safe operation of gas insulation equipment.

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