Infrared spectroscopy falls under the overarching theme of molecular spectroscopy, and is based on the absorption of electromagnetic radiation through molecules. The spectral range of infrared spectroscopy reaches from 2.5 µm to 25 µm. The absorption occurs through translational and rotational vibrations. Only the components CH4, CO, CO2 and H2 can be identified with the infrared measurement device. The first three components are determined directly from the absorption of certain infrared wavelengths. The H2 component, however, is determined through the conductivity of the gaseous mixture, and through the use of the measured concentrations of CO, CO2 and CH4.
A disadvantage of this measurement method is that one analytical unit is only responsible for a single component. Each measuring device can only integrate a maximum of three analytical units. A considerable advantage, however, is that the gas analysis can be completed online. The measuring signal is available within seconds. This fast reaction time allows for the registration of short-term changes in the quality of the gas.