Patent ID: 6228252
Filing Date: 2001-05-08
Classification: G01N

Abstract:
A nitrogen oxide concentration detection apparatus comprising:a main body portion of a sensor having a first measurement chamber and a second measurement chamber, said first measurement chamber including a first oxygen pumping cell, said first oxygen pumping cell being made up of an oxygen ion conducting solid electrolyte layer sandwiched between porous electrodes, said first measurement chamber communicating via a first diffusion rate defining portion with a gas under measurement, said second measurement chamber including a second oxygen pumping cell being made up of an oxygen ion conducting solid electrolyte layer sandwiched between porous electrodes, said second measurement chamber communicating with said first measurement chamber via a second diffusion rate defining portion;an oxygen concentration measurement cell being disposed between said first and second oxygen pumping cells;pump current controlling means for pumping out oxygen from said first measurement chamber by said first oxygen pumping cell so that an output voltage of said oxygen concentration measurement cell will be constant and for controlling the oxygen concentration in said first measurement chamber to a constant value;constant voltage applying means for applying a constant voltage to said second oxygen pumping cell in a direction of pumping oxygen out from said second measurement chamber;nitrogen oxide concentration detection means for detecting the nitrogen oxide concentration in the gas under measurement based on a current flowing in said second oxygen pumping cell on application of said constant voltage;a heater for heating said main body portion of the sensor to a temperature capable of detecting the nitrogen oxide concentration;temperature detection means for directly detecting a temperature of the oxygen concentration measurement cell;heater current controlling means for controlling a current supply to said heater so that the temperature of the oxygen concentration measurement cell detected by said temperature detection means will be a pre-set target temperature; andcorrection means for correcting the nitrogen oxide concentration as detected by said nitrogen oxide concentration detection means depending on a deviation from said target temperature of the oxygen concentration measurement cell detected by said temperature detection means.