Multi-pass absorption enhanced photoacoustic spectrometer based on combined light sources for dissolved gas analysis in oil

Abstract

A highly sensitive multi-pass absorption enhanced photoacoustic (PA) spectrometer (MPAEPAS) based on combined light sources for dissolved gas analysis (DGA) in oil has been presented. A mid-infrared broad-spectrum light source and two distribution feedback (DFB) lasers are longitudinally incident from both ends of a PA cell, respectively. A BaF2 window and a concave mirror with a tiny hole are placed on both ends of the PA cell. The gas dissolved in the oil was pumped into the PA cell by means of headspace degassing. The filtered mid-infrared broad-spectrum light is reflected by the concave mirror to achieve double-pass absorption enhancement for detecting dissolved C2H6, C2H4, CO and CO2 in oil. Additionally, a plane mirror is placed in a filter switching wheel. The lasers for C2H2 and CH4 measurement are incident into the PA cell from the tiny hole opened on the concave mirror. The multi-path absorption enhancement is achieved by reflection of the laser between the concave mirror and the plane mirror. Optical path simulation indicated that the number of laser reflections was more than 20 times. Experimental results shown that the maximum detection errors were all within 30% for the dissolved C2H2, CH4, C2H6, C2H4, CO and CO2 in oil. The detection limits for dissolved C2H2, CH4, C2H6, C2H4, CO and CO2 in oil were 0.5 µL/L, 3 µL/L, 3 µL/L, 3 µL/L, 30 µL/L and 100 µL/L, respectively.