Monitoring of Gas Mixtures by Means of a Flexible IR-Sensor System Utilizing Tunable Filters

Infrared (IR) absorption measurement is a powerful tool for the quantitative concentration analysis in dilute gases , e.g., trace gases and hydrocarbon mixtures. In a pure gas, the absorbance A=log(I/I0), where I0 and I are the incident and detected radiation intensity, respectively, is given by the Beer-Lambert law (BLL). Unfortunately, for the application to an undiluted gas mixture, the required characteristic absorption coefficients are composition- and concentration-dependent, which hampers the application of the BLL in these cases. In this contribution we report on a compact sensor setup aiming at the determination of the mixing ratio of gas mixtures with three components, where only two of the components are IR active. The system is based on a simple IR absorption unit integrated into a sampling pipe enabling operation at ambient pressure and utilizing a tunable IR-filter. The recorded spectra can be processed using partial least square algorithms to determine the composition.