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A new low cost, quick responding, and compact NOx sensor using ZrO2 thick film and the meter have been developed. The sensor is amperometric and consists of two cells: the first cell is an oxygen pumping cell; the second cell is also oxygen pumping cell extracting oxygen from NOx by dissociating it into O2 and N2 gas. The oxygen pumping current in the second cell is proportional to the NOx gas concentration in the second cell and the exhaust gas. The meter is small size, light weight and can measure NOx and A/F ratio at the same time. An unique electronic algorithm is also developed to optimize the electrochemical control system effectively.

In 1999, the first generation NOx sensor from NGK Spark Plug, Co., Ltd. was commercialized for use in gasoline LNT NOx after-treatment systems [ 1 ]. Since then, as emissions regulations and OBD requirements have become more stringent, the demand for a high-accuracy NOx sensor with fast light-off has increased, particularly for diesel after-treatment systems. To meet such market demands, NGK Spark Plug, Co., Ltd. has developed, in collaboration with Ford Motor Company, a second generation NOx sensor.