A new design of the differential photoacoustic gas detector combined with a cantilever microphone

Abstract.A new prototype of a portable differential photoacoustic measurement system was designed and built. The system applies the gas filter correlation method. A blackbody radiator is used as a radiation source, which allows measurements of great variety of different IR absorbing gases. The prototype exploits the high sensitivity of a cantilever pressure sensor. The differential design allows a selective real time measurement for a single gas in open air or from the flowing sample. For the first time the photoacoustic cell geometry for an acceleration noise damping was integrated to a differential detector. The system has potential applications anywhere that sensitive in-situ-measurements are required: for example in process control technology, air quality monitoring, exhale monitoring, alarm devices and food industry. The measurement of nitric oxide was modeled in the presence of water vapor. As an example the concentration of water vapor, that is acceptable if ppb-level nitric oxide measurements are to be done, was calculated. With a typical band pass filter and a blackbody radiator the amount is 20 ppm with 1.3 s integration time. The concentration was also calculated to diode laser operating at 2.663 μm and quantum cascade laser at 5.263 μm. The respective concentrations were 2 ppm and 6600 ppm.