ISO 9060 Solar energy

Specification and classification of instruments for measuring hemispherical solar and direct solar radiation

In the ISO 9060:2018 standard, solar radiation sensors (pyranometers) are classified in three classes:

 previously 
Class ASecondary Standardfor scientific measurement quality
Class BFirst Classfor good measurement quality
Class CSecond Classfor medium measurement quality

The ISO 9060:2018 classification is accepted as well by the WMO (World Meteorological Organisation).