Apogee Instruments SP-230-SS Gebruikershandleiding - Pagina 13
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Sensor Calibration
All Apogee un-amplified pyranometer models have a standard calibration factor of exactly:
Multiply this calibration factor by the measured mV signal to convert sensor output to shortwave radiation in units
-2
of W m
:
Calibration Factor (5.0 W m
5.0
Full Sunlight
(1000 W m
Spectral Errors for Measurements with Silicon-cell Pyranometers
Apogee SP series pyranometers are calibrated under electric lamps in a calibration laboratory. The calibration
procedure simulates calibration under clear sky conditions at a solar zenith angle of approximately 45°. However,
due to the limited spectral sensitivity of silicon-cell pyranometers compared to the solar radiation spectrum (see
graph below), spectral errors occur when measurements are made in conditions that differ from conditions the
sensor was calibrated under (e.g., the solar spectrum differs in clear sky and cloudy conditions, thus measurements
in cloudy conditions result in spectral error because sensors are calibrated in clear sky conditions).
5.0 W m
-2
per mV) * Sensor Output Signal (mV) = Total Shortwave Radiation (W m
*
)
-2
Sensor Output
200 mV
-2
per mV
200
Example of total shortwave radiation
measurement with an Apogee SP-110
pyranometer. Full sunlight yields total shortwave
radiation on a horizontal plane at the Earth's
surface of approximately 1000 W m
an output signal of 200 mV. The signal is
converted to shortwave radiation by multiplying
by the calibration factor of 5.0 W m
-2
)
=
1000
-2
. This yields
-2
per mV.