Importance

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Abstract

An NOx sensor having an electrochemical cell having a solid electrolyte body and a first and a second electrode, a portion that permits restricted communication of the first electrode with an external measurement gas space, a catalyst disposed adjacent the first electrode for decomposing NOx, a device for applying a current between the first and second electrodes, a current measuring device for detecting a current flowing between the first and second electrodes, an oxygen partial pressure measuring device for detecting an oxygen partial pressure of the atmosphere surrounding the first electrode, and a control device for calculating the concentration of NOx contained in the measurement gas in the external space, based on a first and a second current value. The current value is detected by the current measuring device when the oxygen partial pressure detected by the oxygen partial pressure measuring device is higher than a predetermined level above which the decomposition of NOx by the catalyst will not occur and below which the decomposition of NOx will occur. The second current value is detected when the oxygen partial pressure is lower than the predetermined level.

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First Claim