This guide describes available international specifications for the performance classification for instruments that measure hemispherical solar- and direct solar radiation. The guide limits itself to instruments optimized for measurement of the solar irradiance in W/m2. These instruments typically respond over the solar spectrum of wavelengths from 285 nm to 2800 nm, but are calibrated with respect to the internationally recognized World Radiometric Reference maintained by a group of absolute cavity pyrheliometers that respond to radiation out to the far infrared (~50 micrometer) spectral region. The referenced classification schemes are based on a set of instrument specifications published in the referenced documents. The specifications are obtained through characterization experiments, involving indoor as well as outdoor testing. The objective of this guide is to reference the performance classification documents, provide background to the development of the classifications, and provide guidance to the user in using performance classification to select instruments appropriate for the users application. The user should realize that the measurement uncertainty as obtained during outdoor measurements is a function of a) instrument class or classification b) calibration procedure, c) measurement conditions and maintenance, and d) environmental conditions. Therefore statements about the overall measurement uncertainty can only be made on an individual basis, taking all these factors into account. Uncertainty evaluation is covered by ASTM nnnn-nn (Work Item WK 36479) Standard Practice for Uncertainty Evaluation of Calibration and Measurements With Pyranometers and Pyrheliometers.
solar radiation; absolute cavity radiometer; responsivity
There is a need for users of radiometers to have guidance for selecting instrumentation appropriate for their application. Particularly in the solar renewable energy field, selection of a radiometer directly impacts the accuracy and uncertainty in the rating of solar conversion system performance. There is an ISO standard (9060, 1996) for radiometer classification and World Meteorological Organization (WMO) Committee on Instrumentation, Measurements and Observations, (CIMO) Guide, WMO publication No. 8 with descriptions of classification schemes and expected limits of performance with respect to certain parameters. The present ASTM Guide refers to current knowledge and accuracy levels for different levels of radiometer performance. The Guide provides the user a summary of the contents of the referenced publications and references to use for estimating uncertainty in the data from various classes of radiometers in various applications.
The title and scope are in draft form and are under development within this