This pyrheliometer measures the intensity of a radiant beam at normal incidence that comes only from the solar disk which includes about 5° of circumsolar radiation. The sensor of this instrument, designed in conformity with WMO specifications, is mounted on a tracking system to be always directed to the sun. The tracking system incorporates a sun sensor for tracking during clear weather, and changes automatically to a mechanical mode during cloudy weather.
Sensor

Sensitivity: about 4 mV/kW·m^-2

Aperture angle: 2.5° (half angle)

Tracking System

Mechanism: 2-axis pulse motor

Angular step: less than 0.01°

Tracking process: Automatic commutation

     between sun sensor mode