The corresponding experimental system was designed, and the direct absorption technology based on the principle of tunable laser absorption spectrum of inter-band cascade laser (ICL) was used to detect low concentration of sulfur fluoride (SO2F2) gas. The position of 3619 nm is chosen as the measurement spectrum line of SO2F2 gas, which can effectively avoid the cross interference of background components. At 35 ℃ of working temperature and 80 mA of current, the inter-band cascade laser emission wavelength can completely cover the absorption spectrum line at 3619 nm at the center of SO2F2 gas. The direct absorption spectrum of SO2F2 gas after deducting the background absorption is obtained by taking the logarithm of the ratio of the transmitted light intensity to the incident light intensity and the time-frequency conversion of the horizontal axis. The results show that the linear relationship between gas concentration and absorption intensity is good, the fitting coefficient R 2 is 0.997, and the system responsiveness is 0.782 mV/ppm. Three hundred sets of data were collected for 50 min, the relative standard deviation (RSD) was 0.25%, and the system sensitivity was 3.94 ppm. This method can provide a new method for the optical detection of SO2F2 gas, and then provide a reliable experimental basis for the detection of SO2F2 concentration of SF6 decomposition product in GIS gas chamber.
SO2F2 gas is one of the important decomposition products of SF6 in the GIS gas chamber. Based on the analysis of the chemical composition of the gas, the failure prediction of high-voltage electrical equipment can be realized. The SO2F2 gas detection system in the GIS is built based on the second harmonic absorption technology with an inter-band cascade laser with a center wavelength of 3599 nm. The experimental results of the tuning characteristics of the ICL laser show that when the laser works at 35°C and the drive current is 60~100 mA, the emission wavelength of the laser output can cover the wavelength range of 3615.4 nm to 3623.4 nm, which meets the detection requirements of SO2F2 gas at 3619.3 nm. The second harmonic detection results show that the gas harmonic absorption intensity increases with the increase of gas concentration, and the fitted linear correlation R2 is 0.99563, which has a good positive correlation. Collect 300 sets of data, the collection time is 50 minutes, the relative standard deviation (RSD) is 0.29%, and the system detection limit is 357.56 ppb. This method can provide a new method for the optical detection of SO2F2 gas.