Gas sensor and control method of gas sensor

A gas sensor for detecting carbon dioxide and water vapor in a measurement-object gas, the 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 an oxygen-ion-conductive solid electrolyte layer;
• a measurement-object gas flow cavity having a gas inlet that opens on a surface of the base part, a first internal cavity that communicates with the gas inlet via a first diffusion-rate limiting path, and a second internal cavity that communicates with the first internal cavity via a second diffusion-rate limiting path;
• an oxygen pump cell including an intracavity oxygen pump electrode disposed in the first internal cavity of the measurement-object gas flow cavity, and an extracavity oxygen pump electrode disposed at a position different from the measurement-object gas flow cavity on the base part and corresponding to the intracavity oxygen pump electrode;
• a first measurement pump cell including an intracavity first measurement electrode disposed in the second internal cavity of the measurement-object gas flow cavity, and an extracavity first measurement electrode disposed at a position different from the measurement-object gas flow cavity on the base part and corresponding to the intracavity first measurement electrode;
• and
• a second measurement pump cell including:
• an intracavity second measurement electrode disposed at a position opposite to the second diffusion-rate limiting path with respect to the intracavity first measurement electrode in the second internal cavity, or in a third internal cavity that communicates with the second internal cavity via a third diffusion-rate limiting path of the measurement-object gas flow cavity;
• and an extracavity second measurement electrode disposed at a position different from the measurement-object gas flow cavity on the base part and corresponding to the intracavity second measurement electrode;
• the control unit comprises:
• a pump control part for controlling operation of the oxygen pump cell, the first measurement pump cell and the second measurement pump cell, and
• a concentration calculating part for calculating a concentration of each of carbon dioxide and water vapor in a measurement-object gas, wherein
• the pump control part applies a predetermined oxygen pump voltage between the intracavity oxygen pump electrode and the extracavity oxygen pump electrode of the oxygen pump cell to pump out oxygen from the first internal cavity and decompose the water vapor and the carbon dioxide in the measurement-object gas in the first internal cavity,
• the pump control part applies a predetermined first measurement pump voltage between the intracavity first measurement electrode and the extracavity first measurement electrode of the first measurement pump cell to pump oxygen into the second internal cavity and selectively oxidize, in the second internal cavity, hydrogen generated by decomposition of the water vapor, and
• the pump control part applies a predetermined second measurement pump voltage between the intracavity second measurement electrode and the extracavity second measurement electrode of the second measurement pump cell to pump oxygen into near a surface of the intracavity second measurement electrode and selectively oxidize, near the surface of the intracavity second measurement electrode, carbon monoxide generated by decomposition of the carbon dioxide;
• and
• the concentration calculating part calculates a carbon dioxide concentration and a water vapor concentration in the measurement-object gas by:
• considering an oxygen pump current flowing through the oxygen pump cell as a function of the carbon dioxide concentration, the water vapor concentration and an oxygen concentration in the measurement-object gas,
• considering a first measurement pump current flowing through the first measurement pump cell as a function of the water vapor concentration in the measurement-object gas, and the carbon dioxide concentration and/or the oxygen concentration in the measurement-object gas, and
• considering a second measurement pump current flowing through the second measurement pump cell as a function of the carbon dioxide concentration in the measurement-object gas, and the water vapor concentration and/or the oxygen concentration in the measurement-object gas.