Abstract: A method for measuring NOx having a specific discharge lamp. The method controls a photometric analysis device, in which an electrically rotatable filter wheel or shutter wheel is used to change various shutters and/or filters in a beam path with beam source, cuvette and detector. The filter and/or shutter wheel is controlled in such a way that the measurement time is greater than the transfer time. This control improves the detection limit of the NOx resonance absorption method.

Abstract: 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.