Abstract: An apparatus for guiding traveling yarn through a slot in which characteristics of the yarn are sensed, includes a pair of members having surfaces engaging the traveling yarn. The surfaces of the members are spaced from the slot, in respective opposite directions, by an amount sufficient to permit circulation of a fluid therebetween for removing dust and other debris, thereby reducing the distortion of the sensing of the yarn caused by the dust and other debris. The first and second members can be integrally formed from the housing which includes the slot.

Abstract: An apparatus for sensing characteristics of a traveling yarn in response to the shadow cast by the yarn includes a light emitting element and a pair of light sensing elements in opposed relation to the light emitting element. The yarn travels through a slot between the light emitting element and the pair of light sensing elements and is guided such that only a selected one of the light sensing elements is shadowed. An aperture assembly can be positioned between the light emitting element and the slot to channel the emitted light. The aperture assembly includes a plurality of apertures increasing in area in the direction away from the light emitting element and being framed by surfaces inclined away from the light emitting element and decreasingly inclined from frame to frame in the direction away from the light emitting element.