Photoacoustic spectroscopy: Trace CO detection by using 10 mW near-infrared laser and cantilever beam.

Sulfur hexafluoride (SF₆) is commonly used in gas insulated switchgears (GIS) as an insulating medium. When local overheating or partial discharge occurs in GIS, SF₆ may be decomposed into various products including CO. In this paper, based on the photoacoustic (PA) effect of gas molecules, the infrared absorption line at 6380.318 cm⁻¹ was chosen as the target line. An infrared laser with a center wavelength of 1567 nm was chosen as the light source, and a cantilever enhanced PA detector was used as the sensor; then, the experimental platform was constructed. The influence of the temperature and pressure on the infrared absorption coefficient of CO was analyzed. The relationship of the PA signal and the CO concentration under the background of SF₆ and N₂ were obtained. The results show that the temperature has a great influence on the CO absorption coefficient while the influence of pressure is negligible, and the temperature influential coefficient is about 5.0 × 10⁻⁶ cm⁻¹/°C. The detection system has the highest signal-to-noise ratio when the frequency of the chopper is 40 Hz. Under N₂ and SF₆ background gases, there is a good linear relationship between CO concentration and pure PA signals. The minimum detection limit of CO in the background of N₂ is 3.63 ppm, while it is 9.88 ppm in SF₆. The different kinds of the background gases can influence the PA signals. The PA signals decrease with the increase of the temperature of the gas cell, and they also decrease with the increase of the pressure. [ABSTRACT FROM AUTHOR]