Editing Pyranometer (section)

==== Design ====
[[File:SR20 pyranometer linedrawing.pdf|thumb|229x229px|Linedrawing of a pyranometer, showing essential parts: (1) cable, (3) pyranometer and (5) glass domes, (4) black detector surface, (6) sun screen, (7) desiccant indicator, (9) levelling feet, (10) bubble level, (11) connector]]
In order to attain the proper directional and spectral characteristics, a thermopile pyranometer is constructed with the following main components:
* A [[thermopile]] sensor with a black coating. It absorbs all solar radiation, has a flat spectrum covering the 300 to 50,000 nanometer range, and has a near-perfect cosine response.
* A glass dome. It limits the spectral response from 300 to 2,800 nanometers (cutting off the part above 2,800&nbsp;nm), while preserving the 180° field of view. It also shields the thermopile sensor from convection. Many, but not all, first-class and secondary standard pyranometers (see ISO 9060 classification of thermopile pyranometers) include a second glass dome as an additional "radiation shield", resulting in a better thermal equilibrium between the sensor and inner dome, compared to some single dome models by the same manufacturer. The effect of having a second dome, in these cases, is a strong reduction of instrument offsets. Class A, single dome models, with low zero-offset (+/- 1 W/m<sup>2</sup>) are available.

In the modern thermopile pyranometers the active (hot) junctions of the thermopile are located beneath the black coating surface and are heated by the radiation absorbed from the black coating.<ref>{{cite web |url=http://www.kippzonen.com/News/572/The-Working-Principle-of-a-Thermopile-Pyranometer# |title = The Working Principle of a Thermopile Pyranometer - Kipp & Zonen}}</ref> The passive (cold) junctions of the thermopile are fully protected from solar radiation and in thermal contact with the pyranometer housing, which serves as a heat-sink.  This prevents any alteration from yellowing or decay when measuring the temperature in the shade, thus impairing the measure of the solar irradiance.

The thermopile generates a small voltage in proportion to the temperature difference between the black coating surface and the instrument housing. This is of the order of 10 μV (microvolts) per W/m2, so on a sunny day the output will be around 10 mV (millivolts). Each pyranometer has a unique sensitivity, unless otherwise equipped with electronics for [[Calibration|signal calibration]].