A method and apparatus for determining if a sensor is responding to a first substance or a second substance

摘要

A method in which a reactant (for example urea) is added to a substance (ror example NOX gasses in a vehicle exhaust system) to react with said substance is disclosed in which the products of said reaction along with un-reacted portions of the substance and un-reacted portions of the reactant are directed to a sensor 26. The sensor 26 produces an output signal in response to detection of both the un-reacted portions of the substance and the un-reacted portions of the reactant which is used to adjust the amount of reactant added. Said method further determines if the sensor is responding to the substance, or the reactant. A processor 12 is also disclosed for controlling the addition of the reactant to the substance to react with said substance.