For some applications it is desirable, often for economic reasons, to measure NO_x by means of an NO gas analyser in combination with an NO₂ to NO converter.

The principle of the converter is that the gas passes through the heated catalyst material which turns NO₂ into NO. Afterwards the gas is led through the NO analyser and the total NO_x concentration is measured.

The NO analyser used for this purpose is either an IR or UV gas analyser.