Photometer with non-dispersive infraded absorption spectroscopy (NDIR) for measuring several constituents

A photometer for measuring gas components. The photometer has an infrared radiator with radiator modulation, a measuring cell with a measurement and comparison chamber, and a detector which absorbs optopneumatically onto the gas component X, that is filled with gas component X. In order in the case of a photometer of this type to render it possible for a plurality of gas components to be measured with high accuracy and the smallest possible outlay in apparatus, at least one further detector is arranged downstream of the first detector. For the purpose of measuring the gas component Y the further detector is filled with its isotope Y*, and the first detector is optically transparent with regard to the further gas component Y* to be measured or the characteristic absorption bands thereof.