A gas sensor includes: a metal tubular body including a through hole allowing a sensor element to penetrate in an axial direction; and a powder compact being filled between an inner surface of the tubular body constituting the through hole and the sensor element, and sealing between both end portion sides of the sensor element. At least a range of a through hole inner surface to come into contact with the powder compact filled between the inner surface and the sensor element is a stripe-like recessed and projecting region in which projecting portions and recessed portions are alternately arranged in the axial direction and those portions extend along an inner circumferential direction of the tubular body. An interval between the projecting portions in the axial direction is 50 μm to 150 μm. The following expressions are satisfied, 0.3 μm≤Rz1≤10 μm, and Rz1/Rz2≥2.0.

A casing of a gas sensor having a reference gas space therein includes: an outer tube into which an end portion of a sensor element protrudes; and a seal member fit into an end portion of the outer tube to seal the reference gas space, the sensor element includes: a first electrode lead portion including a first electrode lead to electrically connect an outside and at least one out-of-space pump electrode and a first lead insulating layer covering the first electrode lead; and a second electrode lead portion including a second electrode lead that can electrically connect the outside and a measurement electrode and a second lead insulating layer covering the second electrode lead, and A/B<1.00, where A (cm.sup.−1) is diffusion resistance of the first electrode lead portion, B (cm.sup.−1) is diffusion resistance of the second electrode lead portion.

An oxygen sensor is provided in which an insulative coating using an exterior resin material made of insulative resin is applied to a self-heating oxygen sensor element made of a ceramic sintered body housed in a case, and in which waterproof cloths with air permeability are attached using resin adhesives so as to cover openings that connect to air holes on end parts of the case. This allows provision of a gas sensor for use both in air and in liquid having insulating property, waterproof property, and thermal safety.

A gas sensor is configured to inhibit wear of a metal member contacting with a member containing ceramic. The gas sensor comprising: a first member containing ceramic; and a metal member contacting with the first member, wherein a hardness h1 of a contact part of the metal member contacting with the first member is greater than a hardness h2 of a reference part exhibiting a maximum thickness of the metal member.

The invention provides sensing devices for measuring an electrochemical parameter in a reactor. The sensing devices include one or more electrodes, a fastener comprising a female part and a male part, a compressible sealant inside an internal cavity of the male part, a spacer inside the internal cavity of the male part adjacent to and abutting the compressible sealant, a connector for connecting the compressible sealant and the male part and a connector for connecting the spacer and the compressible sealant. The male part, compressible sealant and spacer include one or more channels through which one of the one or more electrodes passes.

A controller of a gas sensor includes: a concentration identification part identifying a concentration of a predetermined gas component based on a measurement pump current flowing between a measurement electrode and an out-of-space pump electrode in accordance with the concentration of the predetermined gas component due to application of a predetermined pump voltage; and a correction processing part correcting the concentration of the predetermined gas component identified by the concentration identification part, the correction processing part corrects the concentration of the predetermined gas component based on a correlation identified in advance between an offset current value as a magnitude of the measurement pump current when a measurement gas not containing the predetermined gas component flows or a normalized value of the offset current value and output fluctuations of the measurement pump current at startup of the gas sensor.

A casing of a gas sensor having a reference gas space therein includes: an outer tube into which an end portion of a sensor element protrudes; and a seal member fit into an end portion of the outer tube to seal the reference gas space, the sensor element includes: a first electrode lead portion including a first electrode lead to electrically connect an outside and at least one inner electrode and a first lead insulating layer covering the first electrode lead; and a second electrode lead portion including a second electrode lead that can electrically connect the outside and a measurement electrode and a second lead insulating layer covering the second electrode lead, and A/B < 1.00, where A (cm.sup.-1) is diffusion resistance of the first electrode lead portion, B (cm.sup.-1) is diffusion resistance of the second electrode lead portion.

A gas sensor includes: a sensor element including a sensing part on a side of one end portion thereof; a casing; and a connector disposed in the casing to electrically connect the sensor element to an outside, wherein the casing includes: an outer tube including a main portion in which a reference gas is included and a sealing portion being an end portion having a smaller diameter than the main portion, another end portion of the sensor element protruding to the main portion, a rubber seal member fitted into the sealing portion to seal the outer tube, and a spacer intervening between the seal member and the connector in the outer tube. The spacer includes a concave portion in an end surface on a side having contact with the connector, and has contact with the connector in the end surface except for the concave portion.

A gas sensor includes: a sensor element including a sensing part on one end portion thereof; a casing; and a connector disposed in the casing to electrically connect the sensor element to an outside, wherein the casing includes: an outer tube including a main portion in which a reference gas is included and a sealing portion with a diameter smaller than the main portion so that another end portion of the sensor element protrudes to the main portion; a rubber seal member fitted into the sealing portion; and a spacer intervening between the seal member and the connector, and the spacer is secured by being sandwiched between the connector and the seal member due to friction force acting on a contact surface with the seal member which occurs by that load acts on the spacer from the seal member in accordance with reduction in the diameter by swaging.

A gas sensor includes, in a single housing section, a substrate mounting surface 31 mounted with a substrate including a light emitter and a light receiver and a mirror section including plural reflectors. Then, in the housing section, all of the plural reflectors are integrally molded on an inner surface of the housing section to multiple reflect light emitted from the light emitter and cause the light to enter the light receiver in an opposing direction of one side and the other side in an extension direction of the substrate mounting surface.