Gas concentration sensing apparatus

摘要

A gas concentration sensor (100) comprises a pump cell (110) for detecting an oxygen concentration in an exhaust gas and a sensor cell (120) for detecting a NOx concentration in the exhaust gas. A porous diffusive layer (101) is interposed between these cells (110, 120). Furthermore, the sensor (100) comprises a heater (103) for heating these cells (110, 120). A control circuit (200) produces a sensor cell voltage having an A.C. component to detect the impedance of sensor cell (120). The electric power supplied to the heater (103) is controlled based on a detected impedance value of the sensor cell (120).