Abstract: Apparatus and method for measuring the surface temperature of an item in a furnace utilizing radiation detection from the item and from a cooled reference plate. The radiation signals derived from the hot item and the cooled reference plate, both of which are positioned in the furnace, are subtracted to provide an output signal which is representative of the item's surface temperature. The reflectance of the hot item and the cooled reference plate are selected to be approximately equal. The reference plate is maintained at a temperature at which it will emit insignificant radiation. When the reflected radiation from the hot item and the cooled reference plate are equal, the difference in radiation received by radiation detection pyrometers will be the radiation emitted by the hot product. The pyrometer outputs, which are subtracted, will accurately represent the hot steel temperature even for changing furnace conditions.

Abstract: The temperature of a metal surface is measured by positioning a radiation detector so that the angle between its optical axis and a line normal to the surface is equal to the principal angle of incidence of the radiation emitted by the surface and interposing a polarizer between surface and radiation detector adjusted to pass only radiation polarized parallel to the plane of emittance. In this way the effects of emissivity variations of the surface are greatly reduced.