Considerable effort at The Eppley Laboratory, Inc., over the past decade has been directed toward the accurate measurement of solar irradiance and the design and development of low temperature blackbodies. Additionally, we have been involved with the design and production of thermopile-type sensors for special applications. The implications of refering all relevant measurements to a unified reference scale of radiation are always of concern. In this paper, self-calibrating radiometers with cavitated receivers which can be designed for a number of total irradiance measurement tasks will be described. Among these tasks are the measurement of solar irradiance, both direct beam and over larger fields-of-view, and the measurement of earth emitted flux (generally from satellites), for which the low temperature blackbodies act as simulators. The radiometer can also be a-dapted to a number of laboratory measurements such as the output of lamp or laser sources. The basic type of sensor employed in the Eppley radiometers is a circular, wirewound and plated thermopile, sometimes called toroidal thermopile. Self-calibration is performed using a heater on the cavity receiver which is employed in an electrical substitution mode. The difference in response produced by the heater to that produced by the radiation source is called the "nonequivalence." Determination and application of the correction factors including the components of the nonequivalence term will be discussed. Results of inter-comparisons with other self-calibrating radiometers will be presented.