Abstract: In the temperature measuring apparatus disposed herein, a first intermediate output signal is obtained which is a function of the ratio of the brightness of a target at two different wavelengths and a second intermediate output signal is generated which is a function of the brightness of the target at a single wavelength. The two intermediate output signals are combined in preselectable proportion to yield a temperature output signal which is relatively insensitive to target surface characteristics.

Abstract: The radiometer disclosed herein is battery operated and employs null balance electronics to obtain high precision in a hand-held instrument. A beam splitting optical system combines an image of the target with an image of an illuminated visual meter registering the temperature measured by the instrument, thereby permitting a target to be readily scanned for temperature variations.

Abstract: In the radiometric apparatus disclosed herein, radiant energy from a target is chopped before reaching a detector element. The same detector element receives radiation from a light-emitting diode which is periodically energized in synchronism with the chopping, the level of the energization of the light-emitting diode being varied as a function of a feedback signal obtained by synchronously demodulating the detector signal. In this manner, the a.c. component of the detector signal is driven to a null balance, the level of energization of the light-emitting diode at balance being indicative of the level of radiation received from the target.