A gas sensor includes a detection circuit unit that detects a specific gas component in measured gas based on output from a sensor element. The detection circuit unit includes an AC voltage application unit that applies an AC voltage signal to a pair of electrode units in an electrochemical cell, a gas concentration detection unit that detects concentration information on the specific gas component from a DC signal component included in an output signal provided by the electrochemical cell, and a cell temperature detection unit that detects temperature information on the electrochemical cell from an AC signal component included in the output signal. The cell temperature detection unit includes a signal extraction unit that removes the DC signal component to separate the AC signal component from the output signal, and a synchronous detection unit that performs synchronous detection on the separated AC signal component using the AC voltage signal.

A first gas sensor having a first sensor element includes a first protective cover that protects the first sensor element, and a second gas sensor having a second sensor element includes a second protective cover that protects the second sensor element. The first protective cover is coated with an oxidation catalyst for one target component from among a plurality of target components, and the second protective cover is coated with an inert catalyst for the one target component.

A first gas sensor having a first sensor element includes a first protective cover that protects the first sensor element, and a second gas sensor having a second sensor element includes a second protective cover that protects the second sensor element. The first protective cover is coated with an oxidation catalyst for one target component from among a plurality of target components, and the second protective cover is coated with an inert catalyst for the one target component.

A gas sensor element for detecting a specific gas component in a measured gas, comprising: an element body in the form of a long plate having a gas detection part at an end thereof on a distal end face side in a longitudinal direction; and a porous protective layer covering an outer periphery of the end on said end face side of the element body, wherein in a cross section including two adjacent ones of the end face and side faces connected to the end face, an outer surface of the protective layer facing an element corner where the two faces meet has a shape with a corner part, and a ratio of an assumed diameter of a water droplet contained in the measured gas in a use environment to an effective length of the corner part in the cross section is equal to or larger than 1.5.

A gas sensor element for detecting a specific gas component in a measured gas, comprising: an element body in the form of a long plate having a gas detection part at an end thereof on a distal end face side in a longitudinal direction; and a porous protective layer covering an outer periphery of the end on said end face side of the element body, wherein in a cross section including two adjacent ones of the end face and side faces connected to the end face, an outer surface of the protective layer facing an element corner where the two faces meet has a shape with a corner part, and a ratio of an assumed diameter of a water droplet contained in the measured gas in a use environment to an effective length of the corner part in the cross section is equal to or larger than 1.5.

Provided is a gas sensor element capable of realizing both highly accurate concentration measurement in environments where the concentration of a specific gas in a measurement target gas is high and highly accurate concentration measurement in environments where the concentration is low. A gas sensor according to one aspect of the present invention adjusts a sensor element drive temperature such that the value of cell resistance of a main pump cell is a predetermined value. Further, in the gas sensor according to one aspect of the present invention, the slope of the cell resistance of the main pump cell is larger than the slope of cell resistance of a measurement pump cell.

Provided is a gas sensor element capable of realizing both highly accurate concentration measurement in environments where the concentration of a specific gas in a measurement target gas is high and highly accurate concentration measurement in environments where the concentration is low. A gas sensor according to one aspect of the present invention adjusts a sensor element drive temperature such that the value of cell resistance of a main pump cell is a predetermined value. Further, in the gas sensor according to one aspect of the present invention, the slope of the cell resistance of the main pump cell is larger than the slope of cell resistance of a measurement pump cell.

Provided is a gas sensor element capable of realizing highly accurate concentration measurement in both environments where the concentration of a specific gas in a measurement target gas is high and where the concentration is low. A gas sensor according to one aspect of the present invention determines whether the concentration of a predetermined gas component in a measurement target gas is higher or lower than a predetermined concentration. If it is determined that the concentration is lower, a specific temperature that a sensor element is to reach as a result of being heated by a heater unit is set to be lower than the specific temperature set if it is determined that the concentration is higher.

Provided is a gas sensor element capable of realizing highly accurate concentration measurement in both environments where the concentration of a specific gas in a measurement target gas is high and where the concentration is low. A gas sensor according to one aspect of the present invention determines whether the concentration of a predetermined gas component in a measurement target gas is higher or lower than a predetermined concentration. If it is determined that the concentration is lower, a specific temperature that a sensor element is to reach as a result of being heated by a heater unit is set to be lower than the specific temperature set if it is determined that the concentration is higher.

Disclosed is a gas sensor element having: a solid electrolyte body containing oxygen-ion conductive ZrO.sub.2; a detection electrode disposed on the solid electrolyte body to be exposed to a gas under measurement; and a reference electrode disposed on the solid electrolyte body to be exposed to a reference gas. In the gas sensor element, the detection electrode contains Pt and ZrO.sub.2; the detection electrode has a thickness of 3 to 10 μm; the amount of ZrO.sub.2 contained relative to Pt in the detection electrode is 12 to 18 wt %; the detection electrode has a porosity of 5% or lower; and, in a particle size distribution graph of ZrO.sub.2 particles in the detection electrode, a cumulative value of peaks appearing in a range of 0.025 μm to 0.200 μm is 60 to 75%, and a cumulative value of peaks appearing in a range of 1.000 μm to 3.162 μm is 2 to 7%.