Patent ID: 6036841
Filing Date: 2000-03-14
Classification: G01N

Abstract:
A method for measuring nitrogen oxide (NOx) in a gas by decomposing NOx in the gas and measuring an amount of oxygen generated by the decomposition, using a sensor comprising:a main pump means including an electrochemical pump cell comprising a substrate comprising an oxygen ion conductive solid electrolyte and an inner pump electrode and an outer pump electrode formed on the inner surface and outer surface of the substrate, respectively, and said main pump means treating oxygen contained in the measuring gas introduced from an external space by pumping processing on the basis of a control voltage applied between said inner pump electrode and said outer pump electrode, andan electric signal conversion means for generating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in the measuring gas after having been treated by the pumping processing by said main pump means, said electric signal conversion means having a pair of detection electrodes where one of the electrodes is on the side where the measuring gas that was treated by pumping processing by said main pump means is introduced;said method for measuring nitrogen oxide (NOx) comprising the steps of:introducing the gas to a first inner space under a first diffusion resistance and connected with said external space,controlling an oxygen partial pressure in an atmosphere in the first inner space to be a predetermined low value at which NO is not decomposed substantially by said main pump means,introducing a controlled atmosphere of the first inner space into a second inner space which is connected with the first inner space and which is under a second diffusion resistance,detecting an oxygen partial pressure in said second inner space with an electrochemical pump cell which is located for detecting an oxygen partial pressure in the second inner space,adjusting said control voltage applied in said main pump cell in dependence on the measurement output of said electrochemical pump cell to maintain the measurement output of said electrochemical pump cell constant, andgenerating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in said atmosphere by said electric signal conversion means.