Patent ID: 6196053
Filing Date: 2001-03-06
Classification: F02D,G01N

Abstract:
A method of measuring a concentration of NOx as a component of a measurement gas, using a sensing device including (a) means for defining an internal chamber which communicates with an external measurement-gas space, (b) diffusion means for introducing said measurement gas into said internal chamber under a predetermined diffusion resistance, (c) first oxygen pumping means having a first pair of electrodes disposed within and outside said internal chamber, respectively, for controlling an oxygen partial pressure of an atmosphere in said internal chamber, (d) second oxygen pumping means having a second pair of electrodes disposed within and outside said internal chamber, respectively, for pumping out from said internal chamber oxygen which is produced by decomposition or reduction of the NOx component of the measurement gas, and (e) current detecting means for detecting an amount of electric current flowing through said second oxygen pumping means, said method comprising the steps of:selecting a material of one of said pair of electrodes of said first oxygen pumping means which is disposed within said internal chamber, and/or controlling at least one of a temperature and the oxygen partial pressure in said internal chamber, such that an ability of said one of said first pair of electrodes as a catalyst to decompose or reduce NO is lower than that of one of said second pair of electrodes which is disposed within said internal chamber; andcontrolling said first oxygen pumping means to effect an oxygen pumping action with respect to said internal chamber, such that a pumping current corresponding to the concentration of said NOx component of said measurement gas flows through said second oxygen pumping means, and so that the oxygen partial pressure of the atmosphere in said internal chamber is regulated to a predetermined level.