Detection of trace C2H2 in N2 buffer gas with cantilever-enhanced photoacoustic spectrometer

Abstract

Acetylene (C2H2) is a flammable and explosive alkyne, which is usually used as a fault feature of oil-immersed transformers. When the concentration of dissolved C2H2 in the transformer oil exceeds 0.1 ppm, it is considered that the transformer has a discharge fault. Therefore, the development of a reliable measurement system that can detect trace amounts of C2H2 is of great significance in the field of industrial equipment failure detection. To this end, this paper built a high-sensitivity cantilever-enhanced photoacoustic spectrometer with a broadband infrared emitter and a detection limit of ∼0.078 ppm with the 1σ confidence level was obtained. Moreover, through the Allan variance analysis, a minimum detection limit of ∼0.008 ppm was obtained when the photoacoustic spectrometer’s sampling time is set to 80 s. Besides, by analyzing the source of the instrument’s background noise, it is found that the vibration noise caused by the mechanical chopper is a significant source of background noise in the photoacoustic signal. Therefore, the photoacoustic spectrometer’s sensitivity can be effectively improved by replacing the traditional mechanical chopper with an electronic chopper. Lastly, the sensitivity of the photoacoustic spectrometer under different optical power of the infrared emitter, the temperature and pressure conditions of the C2H2/N2 gas sample is evaluated. It turns out that as the optical power and gas sample pressure increase, the sensitivity of the photoacoustic spectrometer increases, while as the temperature of the gas sample increases, the sensitivity of the photoacoustic spectrometer decreases.