Apogee SP-214 Owner's Manual - Page 16
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16
MAINTENACE AND RECALIBRATION
Moisture or debris on the diffuser is a common cause of low readings. The sensor has a domed diffuser and housing for
improved self-cleaning from rainfall, but materials can accumulate on the diffuser (e.g., dust during periods of low rainfall,
salt deposits from evaporation of sea spray or sprinkler irrigation water) and partially block the optical path. Dust or organic
deposits are best removed using water or window cleaner and a soft cloth or cotton swab. Salt deposits should be dissolved
with vinegar and removed with a soft cloth or cotton swab. Never use an abrasive material or cleaner on the diffuser.
The Clear Sky Calculator (www.clearskycalculator.com) 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
measurements are still different after a second test, email
to discuss test results and
possible return of sensor(s).