Apogee Instruments SP-230 Owner's Manual - Page 4
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INTRODUCTION
Solar radiation at Earth's surface is typically defined as total radiation across a wavelength range of 280 to
4000 nm (shortwave radiation). Total solar radiation, direct beam and diffuse, incident on a horizontal
surface is defined as global shortwave radiation, or shortwave irradiance (incident radiant flux), and is
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expressed in Watts per square meter (W m
, equal to Joules per second per square meter).
Pyranometers are sensors that measure global shortwave radiation. Apogee SP series pyranometers are
silicon-cell pyranometers, and are only sensitive to a portion of the solar spectrum, approximately 350-
1100 nm (approximately 80 % of total shortwave radiation is within this range). However, silicon-cell
pyranometers are calibrated to estimate total shortwave radiation across the entire solar spectrum.
Silicon-cell pyranometer specifications compare favorably to specifications for World Meteorological
Organization (WMO) moderate and good quality classifications and specifications for International
Organization of Standardization (ISO) second class and first class classifications, but because of limited
spectral sensitivity, they do not meet the spectral specification necessary for WMO or ISO certification.
Typical applications of silicon-cell pyranometers include incoming shortwave radiation measurement in
agricultural, ecological, and hydrological weather networks, and solar panel arrays.
Apogee Instruments SP series pyranometers consist of a cast acrylic diffuser (filter), photodiode, and
signal processing circuitry mounted in an anodized aluminum housing, and a cable to connect the sensor
to a measurement device. Sensors are potted solid with no internal air space and are designed for
continuous total shortwave radiation measurement on a planar surface in outdoor environments. SP series
sensors output an analog voltage that is directly proportional to total shortwave radiation from the sun.
The voltage signal from the sensor is directly proportional to radiation incident on a planar surface (does
not have to be horizontal), where the radiation emanates from all angles of a hemisphere.