Abstract: An ATR sensor has a housing and sensor components in the housing including an electromagnetic radiation source for emitting a predefined wavelength range, a reflection body permeable for radiation and contactable with a fluid to be evaluated, and a detector for the reflected radiation as well as other members for conducting the measurement and for operation. The sensor is particularly suited for measuring a CO2 content of a fluid. Before sealing the housing in a gas-tight manner, in particular for avoiding a measurement value drift and for keeping the radiation paths free of CO2, a CO2 getter material is introduced into the housing and/or into a receiving space of an additional housing that communicates with the interior space of the housing before sealing the interior space and/or the receiving space.

Abstract: The CO2 content in a liquid, in particular a beverage, is to be tested. Three absorption measurements of the liquid are carried out respectively at a wavelength within a first wavelength range between 4200 and 4300 nm to measure a first absorption value with attenuated total reflectance, at a second wavelength within a second wavelength range between 3950 and 4050 nm and a second absorption value with attenuated total reflectance, and at a third wavelength within a third wavelength range between 3300 and 3900 nm and a third absorption value with attenuated total reflectance. A pre-defined model function is used for determining the CO2 content based on the first, second and third absorption values. The model function is applied to the absorption values and the result of the evaluation is kept available as the CO2 content of the liquid to be tested.