WIDE-AREA AIR-FUEL RATIO SENSOR AND DRIVING METHOD THEREOF

PROBLEM TO BE SOLVED: To realize wide range measurement of air/fuel ratio (A/F) by a constitution wherein a measuring electrode functions as an oxygen pumping electrode and a sensing electrode while a sensing reference electrode functions as an oxygen reference electrode. SOLUTION: At a sensor section 31, a measuring electrode 23 and a first pumping electrode 25 are formed on one side face of a solid state electrolytic plate 30 while a second pumping electrode 28 and a sensing reference electrode 26 are formed on the opposite side face. The measuring electrode 23 functions as an oxygen pumping electrode and a sensing electrode while the sensing reference electrode 26 functions as an oxygen reference electrode by receiving oxygen from the first pumping electrode 25. Resistance between the measuring electrode 23 and the second pumping electrode 28 is measured and used in the measurement of excess voltage between the measuring electrode 23 and the sensing reference electrode 26 caused by the pumping current value between the measuring electrode 23 and the second pumping electrode 28. The excess voltage is added to the pumping voltage.