ASTM E941-83(1999) PDF

1.1 This test method covers all pyranometers having calibrations sensitive to tilt.

1.2 This test method combines measurement and calculation, yielding calibration factors derived from many measurements and identified with either a single tilt angle or at normal incidence with one or only a few specific angles of tilt.

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

1.4 Two types of calibrations are covered: Type I employs a self-calibrating pyrheliometer, and Type II calibrations employ a secondary reference pyrheliometer as the standard instrument.

1.5 This test method provides for calibration at fixed south facing tilts from the horizontal with instrument constant data obtained at various angles of incidence throughout the day at that tilt.

1.6 Calibration of reference pyranometers may be performed by a method in which the axis of the sensitive element is aligned with the sun during the shading disk test. This procedure avoids the effect of cosine errors, but emphasizes the importance of tilt corrections.

1.7 The calibration of reference pyranometers at horizontal, that is, with axis vertical, is covered in another ASTM standard (see Section 2).

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