Importance

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Abstract

Using a sole Nox sensor Nox concentration and oxygen concentration are measured accurately. A measurement device for measuring NOx concentration and oxygen concentration comprises an NOx sensor 2 having a first measurement chamber 20 communicating via a diffusion rate regulating layer 4d with the gas under measurement and a second measurement chamber 26 communicating with the first measurement chamber 20 via diffusion rate regulating layers 6d, 22d. A first pump cell 4 and an oxygen concentration measurement Vs cell 6 are formed on the first measurement chamber 20, while a second pump cell 8 is formed on the second measurement chamber 26. Inside of the first measurement chamber 20 is controlled to a constant low oxygen concentration by controlling the first pump current IP1 so that output of Vs cell 6 will equal a reference voltage VC0. By applying a constant voltage across the second pump cell 8 NOx in the second measurement chamber 26 is decomposed to pump out oxygen. Thus NOx concentration and oxygen concentration are measured from the second pump current IP2 and from the first pump current IP1, respectively. During measurement, sensor temperature is detected from the internal resistance of the Vs cell for controlling heater current supplied to heaters 12, 14 to maintain a constant sensor temperature.

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First Claim