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

The invention relates to a photometer using the non-dispersive infrared spectroscopy method, NDIR method for short, having a measuring cell, an infrared radiator with radiator modulation, the measuring cell consisting of a measurement and comparison chamber, and having at least one optopneumatic detector, in accordance with the preamble of Patent Claim . 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.