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Schenk Star pyranometer
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The Schenk
Star pyranometer is a black and white star type pyranometer that has six
black and six white segments. The temperature difference between the black
and white painted sectors is proportional to the incident solar radiation.
Because the measurement is a temperature difference, the measurement should
not be affected as much by ambient temperature.
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Specifications
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Measuring range:
0 to 1500 Wm-2. |
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Spectral sensitivity: 0.3 to 3
µm. |
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Output: about 15
µV/Wm-2 or 4 to 20 µA for
0 to 1500 Wm-2. |
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Impedance: about
35 Ohms. |
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Ambient temperature:
-40 to +60°C. |
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Resolution: < 1
Wm-2. |
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Stability: < 1 %
per year (temporary operation) |
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Cosine response: < 3%
of the value, zenith angle 0° to 80°. |
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Azimuth response: < 3%
of the value. |
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Temperature effect: < 1
% of the value between -20 and +40°C. |
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Linearity: < 0.5%
in the range 0.5 to 1330 Wm-2. |
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Response time: < 25 seconds
(95%), < 45 seconds (99%). |
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Accuracy
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An Eppley PSP, which measures the temperature
difference between a black disk and the body of the pyranometer, has an offset
that results from the black disk radiating to the sky. This effect can be seen
by the small negative irradiance values generated during the night. (This offset
is on the order of 10 W/m2.)
The Schenk pyranometer measures the
temperature difference between the black and white surfaces which both see the
same sky temperature. Therefore, this effect is much smaller for star-type
pyranometers: one W/m2.
For clear day diffuse measurements that
are on the order of 100
W/m2 or less, the offset can cause problems.
At the Eugene station, we are measuring the diffuse radiation with a shade disk,
with both an Eppley PSP and a Schenk Star pyranometer.
Schenk Star pyranometers exhibit systematic
errors when tilted. They also exhibit an azimuthal affect as the responsivity
varies slightly, depending on whether the sun is over a black wedge or a white
wedge.
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© 2022, UO Solar Radiation Monitoring
Laboratory.
Last
revised: April 5, 2022.
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Home page URL: solardata.uoregon.edu |