Calibration Standards
The only accepted world standards for the calibration of radiometers for the measurement of global or direct broadband solar radiation are as below:
ISO 9846
Calibration of a Pyranometer Using a Pyrheliometer as a reference.
ISO 9847
Allows for calibration of a pyranometer indoors (as at the factory in Delft) against a reference pyranometer of similar type, or outdoors. Outdoors a field pyranometer can be calibrated over several days against a ‘reference’ pyranometer of similar or (ideally) higher quality with a reliable, recent, and traceable calibration.
ISO 9059
Calibration of Field Pyrheliometers by Comparison to a Reference Pyrheliometer. This can be against a ‘reference’ instrument of similar type or (ideally) an Absolute Cavity Pyrheliometer. This is the PMO 6 from WRC-Davos or the HF/AHF from Eppley.
ISO 9060
Specification and Classification of Instruments for Measuring Hemispherical Solar and Direct Solar Radiation. These are the standards recommended by the World Meteorological Organization (WMO) and are used by every manufacturer of quality solar radiation sensors. They are also used by many major meteorological organizations to make their own re-calibrations. Otherwise, instruments are normally returned to the manufacturer. Re-calibration is recommended every two years.
For the purpose of Pyranometers, the applicable standard is ISO 9847 and this calibration procedure allows 2 methods:
1/ Field calibration of the test pyranometer by comparison with a ‘working standard’ instrument that is of similar or higher quality. This comparison is done under a clear sky with the sun near zenith.
2/ Calibration in a laboratory of the test pyranometer by comparison with a ‘working standard’ instrument of the same generic type. This calibration is done under a lamp that approximates to the solar spectrum. This is the method used by Kipp & Zonen.
A ‘working standard’ Pyranometer is an instrument that has been calibrated outdoors against the World Radiometric Reference (WRR) at the World Radiation Centre (WRC) in Davos, Switzerland and issued with a calibration certificate. This specifies the sensitivity under the conditions at the time of the calibration (typically temperature and solar zenith angle/air mass). This sensitivity should be corrected for the conditions in the specific test laboratory.
The laboratory test method is closely defined in WMO 9847 to minimize errors. No calibration lamp simulates the solar spectrum well enough for an absolute indoor calibration. The comparison method is designed so that a ‘traceable’ calibration lamp is not needed and is not actually of any benefit. In the past the lamp was usually Tungsten Halogen, but Kipp & Zonen now uses a Metal Halide lamp that has better stability and less infrared heat output. The specific lamp is not critical because it is a comparison test with a working standard pyranometer calibrated at WRC under clear skies with low aerosol content (almost no pollution).
Kipp & Zonen manufactures and sells the CFR Calibration Facility, which meets the WMO / ISO recommendations. The manual can be downloaded from our website and gives details of the full procedure. Our factory calibration equipment is similar, but the procedure is automated. A full calculation of uncertainties in the calibration chain can be provided.
Many organizations around the world, such as NIST in the USA, offer calibration services to industry. They characterize light sources and light detectors, particularly those used in manufacturing processes, safety applications and illuminance (LUX) measurement. However, they are not set up for the calibration of instruments for the measurement of solar radiation.
NIST and similar organizations do not offer an ISO 9847 calibration service and, as explained, the only acceptable traceability is to the World Radiometric Reference (WRR) at the World Radiation Centre in Davos.
ISO/IEC 17025
Since January 1st, 2020 Kipp & Zonen is ISO/IEC 17025 accredited. A copy of the ISO 17025 accreditation certificate can be downloaded here
Quality Management System
ISO 9001
The Quality Management System of Kipp & Zonen B.V. in Delft, the Netherlands, has been certified for the scope as indicated on the ISO9001:2015 certificate.
A copy of the ISO9001:2015 certificate can be downloaded here.