ISO 9846:1993

Overview

ISO 9846:1993 - Solar energy: Calibration of a pyranometer using a pyrheliometer specifies standardized, repeatable methods to transfer a direct-solar radiometer scale (pyrheliometer) to a hemispherical radiometer (pyranometer). The standard is mandatory for calibration of secondary standard pyranometers under ISO 9060 and is recommended when pyranometers are used as reference instruments in intercomparisons. Its purpose is to ensure uniform, reliable pyranometer calibration so that hemispherical solar radiation data used for solar energy testing and simulation are accurate and traceable.

Key topics and technical requirements

• Calibration principle: Two main methods are described - the alternating sun-and-shade method and the continuous sun-and-shade method - both using a pyrheliometer as the reference and a shade-disc device to measure diffuse irradiance.
• Apparatus:
  • Reference pyrheliometer (secondary or first class recommended depending on required accuracy).
  • Shade disc device positioned perpendicular to the sun’s rays; disc radius r and distance d must ensure the disc masks the sun appropriately (r/d defines an angle matching the pyrheliometer field-of-view; disc radius should exceed the pyranometer dome radius by at least d·tan(0.5')).
  • Solar tracker (altazimuth recommended for non-circular receiver symmetry).
  • Data acquisition: precise digital voltmeter with ~1 µV resolution and ~0.1% uncertainty at 1100 W·m‑2; synchronized samples within ~1 s; solar elevation calculation accuracy ~0.1°.
• Measurement site & conditions:
  • Clear or slowly varying sky (scattered clouds permissible if diffuse irradiance remains stable within measurement cycle).
  • Distance between instruments should be