Abstract: A device and process for measuring infra-red radiation for determining the temperature of wires in lengthwise movement in front of a black background of a heated enclosure constituting a black body and emitting infra-red radiation, and comprising two infra-red-transparent convergent lenses for effecting two optical paths through two spaced windows of the enclosure, respectively; a plane mirror for directing the infra-red radiation resulting from each of said optical paths on an infra-red detector; a rotatable notched disc placed close by said lenses so that the obturation and opening of the lenses by the rotating disc produces a "diaphram effect".

Abstract: The measurement of the temperature of a body such as a wire, bar or tube, or a metal sheet, is effected in relation to a black background by providing either a swinging mirror or two flat mirrors and either a concave spherical mirror associated with the flat swinging mirror, or two concave spherical mirrors associated with the two flat mirrors, as well as an infrared radiation detector whose sensitive element receives alternately and successively, after reflection by the flat mirror(s) and collection by the spherical mirror(s), on the one hand, the infrared radiation of the wire and of the black background which surrounds it and, on the other hand, of the black background alone.