System for rotationally securely plugging a sensor into a through passage of a flow channel

A system for rotationally securely plugging a sensor into a through-passage of a flow channel, the sensor including a sensor housing, the through-passage having an inner wall delimiting the through-passage and first and second inside diameters extending respectively along a first axis and a second axis, perpendicular to the first axis, the first inside diameter being greater than the second inside diameter, the plug-in direction of the sensor housing into the through-passage defining a third axis essentially perpendicular to the first and second axis, the sensor housing having a longitudinal extension area along the third axis, which has an outer wall, the sensor housing being pluggable into the through-passage. To ensure rotationally secure assembly of the sensor in its setpoint angular position, at least one protrusion projecting inwardly into the through-passage by a defined dimension is on the inner wall of the through-passage and/or at least one protrusion projecting outwardly by a defined dimension is on the outer wall of the longitudinal extension area of the sensor housing so that the sensor housing, in the plugged-in state, is rotatable in the through-passage no more than 0.5°, and in particular no more than 0.35°, about the z-axis.