Gas sensor

A gas sensor, comprising a sensor element and a control device, the gas sensor configured to measure at least one of a water concentration and a carbon dioxide concentration in a measurement gas,

• wherein the sensor element includes:
• an element body having an oxygen-ion-conductive solid electrolyte layer and a measurement gas flow path provided therein, the measurement gas flow path configured to introduce and flow the measurement gas;
• a first pump cell including a first inner electrode disposed in a first chamber in the measurement gas flow path and a first outer electrode disposed on an outer surface of the element body;
• a second pump cell including a second inner electrode disposed in a second chamber located downstream of the first chamber in the measurement gas flow path and a second outer electrode disposed on the outer surface of the element body;
• and
• a third pump cell including a third inner electrode disposed in a third chamber located downstream of the second chamber in the measurement gas flow path and a third outer electrode disposed on the outer surface of the element body;
• wherein the control device is configured to perform:
• a first pump cell control process for controlling the first pump cell to pump out oxygen from around the first inner electrode to around the first outer electrode, thereby reducing water and carbon dioxide in the measurement gas in the first chamber;
• a second pump cell control process for controlling the second pump cell to pump in oxygen from around the second outer electrode to around the second inner electrode, thereby oxidizing hydrogen generated by reduction of water in the first chamber in the second chamber;
• a third pump cell control process for controlling the third pump cell to pump in oxygen from around the third outer electrode to around the third inner electrode, thereby oxidizing carbon monoxide generated by reduction of carbon dioxide in the first chamber in the third chamber;
• and
• at least one of a water concentration measurement process for measuring a water concentration in the measurement gas based on a second pump current flowing through the second pump cell in the second pump cell control process, and a carbon dioxide concentration measurement process for measuring a carbon dioxide concentration in the measurement gas based on a third pump current flowing through the third pump cell in the third pump cell control process;
• wherein, when a predetermined condition is satisfied, the control device is configured to perform, as a refresh process, at least one of:
• a first refresh process for controlling the first pump cell to pump in oxygen from around the first outer electrode to around the first inner electrode;
• a second refresh process for controlling the second pump cell to pump in more oxygen from around the second outer electrode to around the second inner electrode than in the second pump cell control process;
• and
• a third refresh process for controlling the third pump cell to pump in more oxygen from around the third outer electrode to around the third inner electrode than in the third pump cell control process.