Measuring device with two spectral channels for the determination of gas concentrations - a first and a second light source (12 and 14) emitting light of different wavelength ranges (20 and 22), - the light beams (20 and 22) of which are directed onto an optical unit of the measuring device, in which the light beams (20 and 22) are guided onto the same optical path and into a measuring path, - with a receiving arrangement which receives the light of the two light sources (12 and 14) after passing through the measuring section, wherein the light of the two light sources is detected separately after passing through the measuring section in receivers (38 and 40) which generate receiving signals depending on the incidence of light, - with an evaluation unit for evaluating the received signals and determining a gas concentration therefrom, - wherein a filter wheel arrangement is provided which has at least two filters (G1, G2, 11, 12, K1, K2) and with which the filters can be pivoted into the two beam paths (20, 22) of the light sources (12, 14) for calibration or function control, and - the filter wheel arrangement being arranged in the beam path (20, 22) between the two light sources (12, 14) and the optical unit, and - said filter wheel assembly having at least two pairs of openings (52-1, 52-2; 52-3, 52-4; 52-5, 52-6; 52-7, 52-8) each having first (52-1, 52-3, 52-5, 52-7) and second (52-2, 52-4, 52-6, 52-8) openings, and - the pairs of openings (52-1, 52-2; 52-3, 52-4; 52-5, 52-6; 52-7, 52-8) are arranged such that when the filter wheel arrangement is rotated about an axis of rotation one of the pairs can be pivoted into the two beam paths (20, 22), so that one of the two beam paths (20, 22) passes through the first opening (52-1, 52-3, 52-5, 52-7) and the other beam path (22 or 20) passes through the associated second opening (52-2, 52-4, 52-6, 52-8) simultaneously and - wherein the filters (G1, G2, 11, 12, K1, K2) are arranged in the openings (52-3, 52-4; 52-5, 52-6; 52-7, 52-8), wherein in at least for one pair the openings (52-1 and 52-2) remain free and have no filter. - a first and a second light source (12 and 14) emitting light of different wavelength ranges (20 and 22), - the light beams (20 and 22) of which are directed onto an optical unit of the measuring device, in which the light beams (20 and 22) are guided onto the same optical path and into a measuring path, - with a receiving arrangement which receives the light of the two light sources (12 and 14) after passing through the measuring section, wherein the light of the two light sources is detected separately after passing through the measuring section in receivers (38 and 40) which generate receiving signals depending on the incidence of light, - with an evaluation unit for evaluating the received signals and determining a gas concentration therefrom, - wherein a filter wheel arrangement is provided which has at least two filters (G1, G2, 11, 12, K1, K2) and with which the filters can be pivoted into the two beam paths (20, 22) of the light sources (12, 14) for calibration or function control, and - the filter wheel arrangement being arranged in the beam path (20, 22) between the two light sources (12, 14) and the optical unit, and - said filter wheel assembly having at least two pairs of openings (52-1, 52-2; 52-3, 52-4; 52-5, 52-6; 52-7, 52-8) each having first (52-1, 52-3, 52-5, 52-7) and second (52-2, 52-4, 52-6, 52-8) openings, and - the pairs of openings (52-1, 52-2; 52-3, 52-4; 52-5, 52-6; 52-7, 52-8) are arranged such that when the filter wheel arrangement is rotated about an axis of rotation one of the pairs can be pivoted into the two beam paths (20, 22), so that one of the two beam paths (20, 22) passes through the first opening (52-1, 52-3, 52-5, 52-7) and the other beam path (22 or 20) passes through the associated second opening (52-2, 52-4, 52-6, 52-8) simultaneously and - wherein the filters (G1, G2, 11, 12, K1, K2) are arranged in the openings (52-3, 52-4; 52-5, 52-6; 52-7, 52-8), wherein in at least for one pair the openings (52-1 and 52-2) remain free and have no filter.