NOx sensors AUDI

Nox sensors are used to detect nitrogen gases in hot exhaust gases.

The principle of the operation of the NOX sensor consists in dividing the exhaust gas into nitrogen and oxygen by a catalytically active electrode.

The amount of oxygen is measured in the same way like at a broadband or linear lambda sensor.

The NOX sensor has two chambers. In the first chamber (which resembles a lambda sensor), the oxygen content of the exhaust gas is maintained at approximately 10 parts per million by means of a so-called flow pump. The power required is inversely proportional to the air to fuel ratio and can be used to correct the NOX signal depending on the measured ratio of these two quantities. In the second chamber there is a NOX reaction, a separation of nitrogen and oxygen. The electrical current that is required to maintain an oxygen-free environment in the platinum-rhodium electrode is proportional to the NOX concentration and thus provides a measuring signal.