Abstract: The invention relates to the use of an optical waveguide for optically measuring the temperature of a high-temperature melt, the optical waveguide directing electromagnetic waves from the measuring point to an optical detector and being moved to the measuring point with the aid of a fluid through a line through which the fluid flows. The optical waveguide has a core, cladding and a coating, with the coating consisting of a protective layer and an outer protective sheath. The outer protective sheath is firmly connected to the protective layer.

Abstract: A method for optically determining the temperature of a molten metal with a measuring device, including calibrating a replacement measuring chain by a measuring chain as a system-internal measuring standard. The measuring device includes an optical waveguide, to guide electromagnetic radiation emitted from the metal or from the tip of the optical waveguide to an optical detector, at least one replacement optical waveguide, an optical detector for determining the temperature of the metal from an analysis of the electromagnetic radiation, a measuring chain, in which the optical waveguide is the measurement recorder, and at least one replacement measuring chain, in which a replacement optical waveguide is the measurement recorder. A reeling device includes a conveying device for successive reeling of the optical waveguide from a stock and of the replacement optical waveguide from a replacement stock, a receiving device for a stock and at least one replacement stock.