Gas sensor and concentration measurement method using gas sensor

A gas sensor capable of measuring concentrations of a plurality of sensing target gas components contained in a measurement gas, the measurement gas at least containing water vapor and carbon dioxide, the gas sensor comprising:

• a sensor element having a structure formed of an oxygen-ion conductive solid electrolyte;
• and
• a controller controlling operation of the gas sensor, wherein
• the sensor element comprises:
• a gas inlet through which the measurement gas is introduced;
• a plurality of chambers communicating sequentially from the gas inlet via different diffusion control parts;
• and
• a heater heating the sensor element,
• two of the plurality of chambers are a first measurement chamber and a second measurement chamber, the second measurement chamber being one of the plurality of chambers farthest from the gas inlet, the first measurement chamber being a chamber next to the second measurement chamber,
• the sensor element further comprises:
• an oxygen pumping-out means capable of performing first pumping-out operation to pump out oxygen contained in the measurement gas so that substantially all water vapor and carbon dioxide contained in the measurement gas are reduced before the measurement gas introduced through the gas inlet reaches the first measurement chamber;
• a first measurement pump cell including a first measurement electrode formed to face the first measurement chamber, an out-of-space pump electrode provided at a location other than a location in the plurality of chambers, and a portion of the solid electrolyte present between the first measurement electrode and the out-of-space pump electrode;
• and
• a second measurement pump cell including a second measurement electrode formed to face the second measurement chamber, the out-of-space pump electrode, and a portion of the solid electrolyte present between the second measurement electrode and the out-of-space pump electrode,
• the first measurement pump cell is capable of pumping oxygen into the first measurement chamber to selectively oxidize, in the first measurement chamber, hydrogen generated by reduction of water vapor associated with the first pumping-out operation and contained in the measurement gas introduced into the first measurement chamber,
• the second measurement pump cell is capable of pumping oxygen into the second measurement chamber to oxidize, in the second measurement chamber, carbon monoxide generated by reduction of carbon dioxide associated with the first pumping-out operation and contained in the measurement gas introduced into the second measurement chamber,
• the controller identifies:
• a concentration of water vapor contained in the measurement gas based on a magnitude of a current flowing between the first measurement electrode and the out-of-space pump electrode when oxygen is pumped into the first measurement chamber by the first measurement pump cell;
• and
• a concentration of carbon dioxide contained in the measurement gas based on a magnitude of a current flowing between the second measurement electrode and the out-of-space pump electrode when oxygen is pumped into the second measurement chamber by the second measurement pump cell,
• the oxygen pumping-out means is further capable of performing second pumping-out operation for a predetermined time period in the middle of the first pumping-out operation, the second pumping-out operation being operation to pump out oxygen contained in the measurement gas to the extent that water vapor and carbon dioxide contained in the measurement gas before reaching the first measurement chamber are not reduced, and
• reduction of water vapor and carbon dioxide by the oxygen pumping-out means is interrupted upon start of the second pumping-out operation, so that water vapor generated in the first measurement chamber and carbon dioxide generated in the second measurement chamber are emitted outside the sensor element.