Abstract: Provided is a gas sensor including a housing made of metal through which a sensor element is inserted and an outer cylinder made of metal welded to an outer periphery of the housing, in which generation of pinholes on a surface of a welded portion is suppressed. In a gas sensor according to one aspect of the present invention, a contact distance Lg, which is a length in an axial direction of an outer peripheral surface of a housing in contact with an inner peripheral surface of an outer cylinder on a rear end side with respect to a molten portion of the outer cylinder formed by welding, is equal to or less than a reference distance Lr.

Abstract: The sensor of a fluid sensor system includes an outer peripheral sensor unit including three or more sensor pairs to surround and sandwich the heating element. The computing device of the system includes a first identification unit identifies a sensor pair in which an output difference between an output value corresponding to a temperature detected by one temperature sensor of the sensor pair and an output value corresponding to a temperature detected by the other temperature sensor of the sensor pair is largest, a second identification unit identifies other sensor pairs adjacent to the identified sensor pair in the circumferential direction, and a flow direction estimation unit estimates the flow direction of the fluid on the basis of the output difference in the sensor pair having the largest output difference and output differences in the other sensor pairs adjacent to the sensor pair in the circumferential direction.