Comparison of infrared sources for a differential photoacoustic gas detection system

A prototype of the differential photoacoustic measurement system with an optical cantilever microphone has been developed. The system is based on gas filter correlation method. The proposed system allows real-time measurement of various IR-absorbing gases from the flowing sample or in the open air. Three setups with different kind of infrared sources were carried out to study selectivity and sensitivity of the prototype and applicability of the source types with differential method. The sources were a mechanically chopped blackbody radiator, electrically chopped blackbody radiator and mechanically chopped CO2-laser. A detection limit for C2H4 was estimated with all three infrared sources. Cross sensitivity and detection limits of gases CH4, C2H4 and CO2 were measured with the mechanically chopped blackbody radiator. This crossinterference matrix was also modeled using HITRAN database and completed with CO and H2O. The measurements indicate that at least ppb-level detection of ethylene using CO2-laser, sub-ppm level with mechanically chopped blackbody and ppm-level with electrically modulated blackbody is possible with a proposed differential system.