In LMDC calibration of pyranometers is carried out according to ISO 9847:1992. According to this process, the istruments under calibration are placed in outdoor conditions, on a horizontal surface, close to the standard Kipp & Zonen CM21 pyranometer (Secondary Standard according to ISO 9060:1990 and High Quality according to WMO).Under constantly clear sky conditions, momentary measurements of electrical voltage are taken at the instruments output during whole daylight period and for solar altitude greater than 20 degrees.
Calibrations are carried out comparatively, using calibrated working standards, with readings traceable to the Global Radiometric Scale. This method is simple and provides sufficient accuracy because errors related to the dependence on solar incidence angle and the instrument's spectral response are avoided.
Traceability is ensured as the 'secondary standard' used in LMDC, is calibrated regularly at the World Radiation Center (WRC), in Davos, Switzerland.
Calibration of photometers is carried out in a manner analoqous to ISO 9847:1992, using a digital reference photometer LMT B510A, with an LMT P30SCT sensor, operational range 0.001-600000 Lux, accuracy of sensitivity better than +/ - 0.5%.
The cost of calibration is 180 euros per actinometer (plus VAT when applicable).