Apogee SP-214-SS Owner's Manual - Page 8

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Apogee SP-214-SS Owner's Manual
Cosine Response
Directional, or cosine, response is
defined as the measurement error at
a specific angle of radiation incidence.
Error for Apogee silicon-cell
pyranometers is approximately ± 2 %
and ± 5 % at solar zenith angles of 45°
and 75°, respectively.
Mean cosine response of eleven Apogee
silicon-cell pyranometers (error bars
represent two standard deviations
above and below mean). Cosine
response measurements were made
during broadband outdoor radiometer
calibrations (BORCAL) performed during
two different years at the National
Renewable Energy Laboratory (NREL) in
Golden, Colorado. Cosine response was
calculated as the relative difference of
pyranometer sensitivity at each solar
zenith angle to sensitivity at 45° solar
zenith angle. The blue symbols are AM
measurements, the red symbols are PM
measurements.