Apparatus for measuring surface temperatures by infrared radiation therefrom

Claim 1

Apparatus for measuring the temperature at the surface of an object by measurement of the infrared radiation emitted from the surface which comprises a compensating radiator in the form of a thermally conductive metallic body having a radiation cavity in one side thereof facing towards the surface of the object to be measured, means for heating said metallic body, a rotatable chopper wheel located within said radiation cavity and which is interposed between the surface of the object and the surface forming the radiation cavity in said metallic body, the side of said chopper wheel facing towards said cavity forming surface being radiation reflective and said chopper wheel being carried by a shaft extending outwardly through a bore in said metallic body and which is connected to a driving motor, an infrared radiation detector positioned outside of said metallic body and which receives in alternation by way of a second bore leading outwardly through said metallic body from said radiation cavity the infrared radiation emitted from the surface of the object and which passes intermittently through said rotating chopper wheel and infrared radiation emitted by the cavity forming surface of said metallic body and which is reflected intermittently into said detector from the reflective side of said chopper wheeL, said detector producing at its output an alternating current signal determined by any temperature differential existing between the object and said metallic body, and means for controlling the supply of heat to said metallic body in accordance with said alternating current signal in such sense as to reduce said signal to zero whereby the temperature of said metallic body then equals the temperature of the object.