From all SMP’s only the SMP11 has an external replaceable drying cartridge, all other have an internal desiccant that is guaranteedfor 10 years.SMP3 is smaller and lighter than the other SMP series pyranometers. It features a 64-junction thermopile sensing element witha highly absorptive and spectrally flat black coating to capture incoming radiation and convert it to an electrical signal. Thisdetector is protected by a high quality glass dome which is 4 mm thick. The housing is completely sealed.SMP 6 uses the same sensing element as SMP3 but has improved performance due to the double glass dome construction andthe increased thermal mass of the larger housing. The glass used has better transmission of ultraviolet radiation than the SMP3glass. The two high quality concentric domes, 2 mm thick, reduce directional error and improve thermal isolation.SMP10 and SMP11 have a 32-junction thermopile sensing element which features faster response, better linearity and a widermeasurement range than the SMP3 and SMP6. SMP10 and SMP11 have built-in temperature compensation. The SMP10 hasinternal desiccant that lasts for 10 years and the SMP11 has a removable drying cartridge.SMP21 is similar to the SMP11 but has individually optimised temperature compensation and a sensor is fitted to monitor thehousing temperature. Each instrument is supplied with its own temperature and directional response for post-processing ofrecorded data by the user. A Pt-100 temperature sensor can be ordered instead of the standard 10 k thermistor.SMP22 has all the features of SMP21 but uses two 4 mm thick very high quality quartz domes for a wider spectral range andreduced thermal offsets. Because of the high optical quality and refractive index of these domes the directional error is greatlyreduced.Features and specifications of all SMP pyranometers are explained later in this manual.1.1.2 International StandardsSMP3 is fully compliant with the requirements of ISO 9060:1990 for a Second Class Pyranometer.SMP6 is fully compliant with the requirements of ISO 9060:1990 for a First Class Pyranometer.SMP10, SMP11, SMP21 and SMP22 are fully compliant with the requirements of ISO 9060:1990 for a Secondary Standard Pyranometer.SMP series pyranometers are calibrated in accordance with Annex A.3 of ISO 9847 ‘Calibration of Field Pyranometers byComparison to a Reference Pyranometer’. Annex A.3 refers to ‘Calibration Devices Using Artificial Sources’. Calibrations aretraceable to the World Radiometric Reference (WRR) in Davos, Switzerland.SMP series pyranometers comply with IEC 60904-1 ‘Photovoltaic devices - Part 1: Measurement of Photovoltaic Current-VoltageCharacteristics’.10