Device and process for determining the concentration of at least one gas component in a breathing gas mixture

A device and process are provided for determining the concentration of at least one gas component in a breathing gas mixture. The device is used especially to determine the concentration of a trace gas for a lung function measurement. The requirements on such a device are compact design with low weight, and the requirement on the process is high speed of measurement. For the case of the determination of the concentration of a gas component in a breathing gas mixture, the device has two detectors designed as thermopiles (3, 4) for the infrared optical radiation of a radiation source (1), of which the first thermopile (3) is used alternatingly as a reference detector and for the determination of the concentration of a trace gas for the lung function measurement, and the second thermopile (4) is used to determine the concentration of a gas component in the breathing gas mixture. The device preferably has a two-layer housing structure (5), comprising an outer, heat-insulating layer (6) and an inner layer (7) with good thermal conductivity and high heat capacity.