an instrument for measuring the intensity of direct solar radiation at normal incidence and can be a primary standard instrument

An instrument used for meauring direct beams of solar irradiance. Uses an aperature of 5.7 deg. to transcribe the solar disc.

instrument with a narrow (circumsolar) field of view which measures direct normal irradiance. Pyrheliometers are mounted on sun-following trackers so that the instrument is always aimed at the sun.

An instrument for measuring the intensity of direct solar radiation at normal incidence. See Angstrom compensation pyrheliometer, Eppley pyrheliometer, Michaelson actinograph, silver-disc pyrheliometer, spectropyrheliometer, water-flow pyrheliometer.

An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc.

A device that measures the intensity of direct beam solar radiation.