Patent ID: 7461523

Claim:
A melting furnace having a crucible and an apparatus for contactless temperature measurement of a melting charge located in the melting crucible ( 2 ) inside the melting furnace by means of a pyrometer ( 5 ) with an optical system ( 8 ) and at least one sensor ( 6 ) optically connected to said optical system ( 8 ), wherein said optical system ( 8 ) can be directed by means of a sight glass ( 18 ) onto at least one section of the melting crucible ( 2 ), wherein the optical system further comprises a tube ( 17 ) which is connected at its upper end ( 31 ) to the sight glass ( 18 ), and extends into a melting chamber ( 11 ) of the melting furnace and points in the direction of the melting crucible ( 2 ), and where the tube has a lower end that is open to the crucible and has a length and inner diameter sufficient to inhibit smoke and particulates from entering the tube.