1.1 This method covers the calibration of reference pyranometers with field angles of 180° (2[pi] steradians) utilizing self-calibrating absolute cavity pyrheliometers having field angles of 5.0° and slope angles of 0.75 to 0.8° as the primary reference instrument.

1.2 This method is applicable to reference pyranometers regardless of the radiation receptor employed.

1.3 Two types of calibrations are covered: (1) Type I employs a self-calibrating absolute cavity pyrheliometer, and (2) Type II calibrations employ a secondary reference pyrheliometer as the standard instrument.

1.4 This standard calibration of reference pyranometers covers the sensitive element in the horizontal plane only, that is, with the axis vertical. The calibration of reference pyranometers at various tilt angles is covered in another ASTM standard (see Section 2.).

1.5 This method is only applicable to calibration procedures using light from the sun.