A gas sensor includes an element body, a pump cell, an impedance measurer, and a calculation unit. The pump cell has an inner electrode disposed in a measurement-object gas flow section of the element body, and an outer electrode disposed outside an element body to come into contact with a measurement-object gas, the pump cell being configured to adjust an oxygen concentration in a vicinity of the inner electrode. The impedance measurer performs first measurement to measure a first impedance by applying a voltage having a first frequency to the pump cell, and second measurement to measure a second impedance by applying a voltage having a second frequency higher than the first frequency to the pump cell. The calculation unit calculates the reaction resistance index correlated with the reaction resistance of the pump cell, based on the first and second impedances.

A gas sensor includes a sensor element and a control unit for controlling the sensor element. The sensor element includes: an adjustment pump cell for adjusting an oxygen concentration in a measurement-object gas to a desired concentration; a current measurement pump cell for detecting a target gas to be measured in the measurement-object gas as a current value, the current measurement pump cell including: an inner measurement electrode and an outer measurement electrode; a reference electrode; and an electromotive force detection sensor cell for detecting an electromotive force value between the inner measurement electrode and the reference electrode. The control unit includes a switching unit for switching whether a current flows through the current measurement pump cell or not.

A gas sensor includes a sensor element and a control unit for controlling the sensor element. The sensor element includes: an adjustment pump cell for adjusting an oxygen concentration in a measurement-object gas to a desired concentration; a current measurement pump cell for detecting a target gas to be measured in the measurement-object gas as a current value, the current measurement pump cell including: an inner measurement electrode and an outer measurement electrode; a reference electrode; and an electromotive force detection sensor cell for detecting an electromotive force value between the inner measurement electrode and the reference electrode. The control unit includes a switching unit for switching whether a current flows through the current measurement pump cell or not.

A sensor element for detecting a physical property of a gas includes: a solid electrolyte film; a first end area and a second end area situated diametrically opposite in the longitudinal direction; a functional element in the first end area in the interior which is electrically conductively connected to a contact surface situated in the second end area on the outer surface, the electrically conductive connection having a strip conductor running essentially in the longitudinal direction in the interior of the sensor element; and a reference gas channel running essentially in the longitudinal direction of the sensor element communicating with a reference gas outside of the sensor element via a reference gas opening, the strip conductor and the reference gas channel being situated in such a way that at least a partial overlap occurs between them.

A gas sensor element includes a main body having a solid electrolyte body on which a measurement gas-side electrode and a reference gas-side electrode are provided, a trap layer covering an outer peripheral surface of the main body to trap poisoning substances contained in a measurement gas, and a waterproof protective layer covering an outer peripheral surface of the trap layer. In the protective layer, there is formed at least one measurement gas introduction port for introducing the measurement gas to the measurement gas-side electrode via the trap layer.

A gas sensor element includes a main body having a solid electrolyte body on which a measurement gas-side electrode and a reference gas-side electrode are provided, a trap layer covering an outer peripheral surface of the main body to trap poisoning substances contained in a measurement gas, and a waterproof protective layer covering an outer peripheral surface of the trap layer. In the protective layer, there is formed at least one measurement gas introduction port for introducing the measurement gas to the measurement gas-side electrode via the trap layer.

A connector has a fixing hole in an intermediate portion of a terminal member, and has an engagement portion projecting downward in a thickness direction, at an end portion at a front end side of the fixing hole. Therefore, when the terminal member is attached to a housing, movement of the terminal member toward a rear end side can be restricted by fitting a projection portion of the housing into the fixing hole. Furthermore, since the engagement portion is provided to the terminal member, movement of the terminal member toward the rear end side can be restricted by engaging the engagement portion with a front end surface of a protrusion portion of the housing.

A connector has a fixing hole in an intermediate portion of a terminal member, and has an engagement portion projecting downward in a thickness direction, at an end portion at a front end side of the fixing hole. Therefore, when the terminal member is attached to a housing, movement of the terminal member toward a rear end side can be restricted by fitting a projection portion of the housing into the fixing hole. Furthermore, since the engagement portion is provided to the terminal member, movement of the terminal member toward the rear end side can be restricted by engaging the engagement portion with a front end surface of a protrusion portion of the housing.

A portable hand-held oxygen monitor for monitoring oxygen in a weld zone includes a user interface having an alphanumeric display and one or more user interface buttons. An audiovisual alarm includes an indicator light and an audio output device, the indicator light being separate and distinct from the alphanumeric display. The oxygen monitor implements an oxygen monitoring mode responsive to activation of one or more of the user interface buttons, wherein (1) a gas sample is obtained, (2) a digital gas sample oxygen level value is generated, and (3) the gas sample oxygen level value is compared to a stored oxygen level alarm value, and the audiovisual alarm is activated if the gas sample oxygen level value is less than the oxygen level alarm value. The activating includes illuminating the indicator light and generating sound from the audio output device to alert a monitor user that is safe to weld.

A portable hand-held oxygen monitor for monitoring oxygen in a weld zone includes a user interface having an alphanumeric display and one or more user interface buttons. An audiovisual alarm includes an indicator light and an audio output device, the indicator light being separate and distinct from the alphanumeric display. The oxygen monitor implements an oxygen monitoring mode responsive to activation of one or more of the user interface buttons, wherein (1) a gas sample is obtained, (2) a digital gas sample oxygen level value is generated, and (3) the gas sample oxygen level value is compared to a stored oxygen level alarm value, and the audiovisual alarm is activated if the gas sample oxygen level value is less than the oxygen level alarm value. The activating includes illuminating the indicator light and generating sound from the audio output device to alert a monitor user that is safe to weld.