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

• A high precision multi-pass absorption enhanced photoacoustic (PA) spectrometer (MPAEPAS) is presented for the dissolved gas analysis. • A mid-infrared broad-spectrum light source and two distribution feedback lasers are used for detection of multi-component gas degassed by headspace degassing. • A mid-infrared broad-spectrum light source is reflected by a concave mirror to achieve double-pass absorption enhancement. • The laser is reflected more than 20 times between the concave mirror and a plane mirror, achieving multi-path absorption enhancement. 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 BaF 2 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 C 2 H 6 , C 2 H 4 , CO and CO 2 in oil. Additionally, a plane mirror is placed in a filter switching wheel. The lasers for C 2 H 2 and CH 4 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 C 2 H 2 , CH 4 , C 2 H 6 , C 2 H 4 , CO and CO 2 in oil. The detection limits for dissolved C 2 H 2 , CH 4 , C 2 H 6 , C 2 H 4 , CO and CO 2 in oil were 0.5 µL/L, 3 µL/L, 3 µL/L, 3 µL/L, 30 µL/L and 100 µL/L, respectively.