This pyranometer is a development of the well-known Eppley 10- and 50-junction 180° pyrheliometer originally introduced by Kimball and Hobbs in 1923.
The detector is a differential thermopile with the hotjunction receivers blackened and the cold junction receivers whitened.
The element is of radial wirewound-plated construction with the black segments coated with 3M black and the white with Barium Sulfate. Built-in temperature compensation with thermistor circuitry is incorporated to free the instrument from effects of ambient temperature. A precision ground optical glass hemisphere of Schott glass WG295 uniformly transmits energy from 285 to 2.800 millimicrons. This hemispherical envelope seals the instrument from the weather, but is readily removable for instrument repair. The cast aluminum case carries a circular spirit level and adjustable leveling screws. There is also a desiccant, which can be inspected readily.
In early 1977, a design change was incorporated in the sensing element to resolve a previous problem of error when the instrument was used other than horizontally. Current models can be used on a tilt or at any orientation with no effect on sensitivity. Included is a calibration certificate traceable to the World Radiation reference which includes conversion factors for different energy units. The RainWise Black and White Pyranometer is manufactured by Eppley and is covered under their warranty.