9. Maintenance, calibration, and
troubleshooting
NOTE:
All factory repairs and recalibrations require a returned material authorization (RMA) and
completion of the “Statement of Product Cleanliness and Decontamination” form. Refer to
the
page at the end of this manual for more information.
9.1 Maintenance
Moisture or debris on the filters (diffuser for upward-looking pyranometer, glass window for
downward-looking pyranometer, silicon windows for pyrgeometers) is a common cause of
errors. Remove dust or organic deposits by using water or window cleaner and a soft cloth or
cotton swab. Remove salt deposits by using vinegar and a soft cloth or cotton swab.
CAUTION:
Never use an abrasive material or cleaner on the diffuser.
9.2 Calibration
The Clear Sky Calculator (
) can be used to determine the need for
pyranometer recalibration. It determines total shortwave radiation incident on a horizontal
surface at any time of day at any location in the world. It is most accurate when used near solar
noon in spring and summer months, where accuracy over multiple clear and unpolluted days is
estimated to be ±4% in all climates and locations around the world. For best accuracy, the sky
must be completely clear, as reflected radiation from clouds causes incoming radiation to
increase above the value predicted by the clear sky calculator. Measured values of total
shortwave radiation can exceed values predicted by the Clear Sky Calculator due to reflection
from thin, high clouds and edges of clouds, which enhances incoming shortwave radiation. The
influence of high clouds typically shows up as spikes above clear sky values, not a constant offset
greater than clear sky values.
To determine recalibration need, input site conditions into the calculator and compare total
shortwave radiation measurements to calculated values for a clear sky. If sensor shortwave
radiation measurements over multiple days near solar noon are consistently different than
calculated values (by more than 6 %), the sensor should be cleaned and re-leveled. If
SN500SS Net Radiometer
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