Patent ID: 6224727
Filing Date: 2001-05-01
Classification: G01N

Abstract:
An NO.sub.x sensor for measuring the NO.sub.x concentration of a measurement gas, comprising:solid electrolyte layers arranged in the form of a laminate having a laminating direction,a first measurement space including a first oxygen pumping cell and an oxygen concentration measuring cell and communicating with the measurement gas via a first diffusion controlling layer, said first oxygen pumping cell comprising an oxygen ion conductive solid electrolyte and porous electrodes disposed on opposite surfaces of the oxygen ion conductive solid electrolyte layer, and said oxygen concentration measuring cell comprising an oxygen ion conductive solid electrolyte layer and porous electrodes disposed on opposite surfaces of the oxygen ion conductive solid electrolyte layer;a second measurement space including a second oxygen pumping cell and communicating with said first measurement space via a second diffusion controlling layer, said second oxygen pumping cell comprising an oxygen ion conductive solid electrolyte layer and porous electrodes disposed on opposite surfaces of the oxygen ion conductive solid electrolyte layer;wherein the electrode layers are arranged in the form of a laminate having a laminating direction,means for maintaining an output voltage of said oxygen concentration measuring cell at a constant value, which means comprises said first oxygen pumping cell for pumping cell for pumping oxygen from said first measurement space; andmeans for applying a constant voltage to said second oxygen pumping cell for pumping oxygen from said second measurement space, whereby the concentration of NO.sub.x contained in the measurement gas can be determined by measuring the current flowing through said second oxygen pumping cell; andwherein said oxygen concentration measuring cell is disposed in a position such that the amount of oxygen contained in the measurement gas flowing from said first measurement space into said second measurement space via said second diffusion controlling layer can be determined without being affected by the distribution of oxygen within said first measurement space; andwherein said second diffusion controlling layer comprises a porous solid electrolyte layer capable of controlling diffusion of the measurement gas, and the electrode of said oxygen concentration measuring cell located on the side of said first measurement space is formed on a portion of said second diffusion controlling layer; andwherein said second diffusion controlling layer at least partially overlaps said first diffusion controlling layer in the laminating direction of said laminate.