26)Describe the working of angstrom pyrheliometer with diagram.

ANGSTROM PYRHELIOMETER

Features:

• Measures direct solar irradiance from 300-4000 nm at normal incidence.
• Sensor: Two blackened identical mangnin strips in thermal contact with thermocouples but electrically insulated.
• Sensor mounted in a long metallic tube to collimate the beam and minimize the effect of scattered irradiance.
• Shutter provided to shield one of the strips alternately.
• The heating by direct irradiation received by the exposed strip is compensated by electrically heating the shielded strip.
• Electrical power required for heating the shielded strip is proportional to incident irradiance.
• Used for instantaneous measurement of direct solar irradiance, is capable of very high accuracy and has very high stability. When used with coloured glass broad band pass filter we get spectral distribution of direct solar irradiance

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Mukesh Sharma
askIITians Faculty