What is a Pyranometer ? Explain the working principle of it with the help of a neat sketch.

Question
Question :

What is a Pyranometer ? Explain the working principle of it with the help of a neat sketch.
Answer

Answer :

Pyranometer – A pyranometer is an instrument, which can measure global radiation, over a hemispherical field of view. It is usually designed on a horizontal surface but can also work on an inclined surface. When the beam radiation is prevented from falling on the instrument sensor, by providing a shading ring, the pyranometer measures the diffused radiation.
A precision pyranometer designed by Eppley Laboratory, USA is shown in diagram. It operates on the principle of thermopile. The sun’s radiation is allowed to fall on a circular, black surface to which the temperature difference between hot and cold junctions of thermopile generates an e.m.f. which is proportional to the solar radiation. Two concentric hemispherical glass domes are used to shield the sensing element from wind and rain. The voltage output of this instrument is approximately 9 µV/W/m2 and output impedance is 650Ω.
 
Pyranometer
Pyranometer

The output of a pyranometer can be obtained either on an electronic chart or an integrated digital printout system.