Control method of gas sensor

A gas sensor comprising a sensor element and a control unit for controlling the sensor element, wherein

• the sensor element comprises:
• a base part in an elongated plate shape, including a plurality of oxygen-ion-conductive solid electrolyte layers stacked;
• a measurement-object gas flow part for introduction and flow of a measurement-object gas through one end part in a longitudinal direction of the base part;
• a main pump cell for adjusting an oxygen concentration in the measurement-object gas to a desired concentration, the main pump cell including:
• an inner main pump electrode disposed on an inner surface of the measurement- object gas flow part;
• and an outer pump electrode disposed at a position different from the measurement-object gas flow part on the base part and corresponding to the inner main pump electrode;
• a measurement pump cell for detecting NOx in the measurement-object gas, the measurement pump cell including:
• a measurement electrode disposed at a position farther from the one end part in the longitudinal direction of the base part than the inner main pump electrode on the inner surface of the measurement-object gas flow part;
• and an outer pump electrode disposed at a position different from the measurement-object gas flow part on the base part and corresponding to the measurement electrode;
• a heater for heating the base part;
• and
• a reference electrode disposed inside the base part to be in contact with a reference gas, and
• the control unit comprises:
• an activity determining part for determining whether the sensor element is in a measurable active state or not;
• a heater control part for controlling a temperature of the heater;
• and
• a pump control part for operating the main pump cell and the measurement pump cell to detect NOx in the measurement-object gas, wherein the activity determining part determines whether the sensor element is in the measurable active state or not;
• the heater control part heats the sensor element by the heater up to an active temperature at which the activity determining part determines that the sensor element is the measurable active state, and further heats the sensor element up to a steady driving temperature;
• and
• the pump control part starts to operate the main pump cell and the measurement pump cell when the sensor element reaches the active temperature, and further continues to operate the main pump cell and the measurement pump cell when the sensor element reaches the steady driving temperature, and wherein
• an oxygen concentration in the measurement-object gas flow part adjusted by the main pump cell when the sensor element reaches the active temperature is higher than an oxygen concentration in the measurement-object gas flow part adjusted by the main pump cell when the sensor element reaches the steady driving temperature.