MAINTENANCE AND RECALIBRATION
Blocking of the optical path between the target and detector can cause low readings. Occasionally, accumulated
materials on the diffuser of the sensor can block the optical path in three common ways:
1.
Moisture or debris on the diffuser.
2.
Dust during periods of low rainfall.
3.
Salt deposit accumulation from evaporation of sea spray or sprinkler irrigation water.
Apogee Instruments quantum sensors have a domed diffuser and housing for improved self-cleaning from rainfall,
but active cleaning may be necessary. 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 cloth or cotton
swab.
Salt deposits cannot be removed with solvents such as alcohol or acetone.
Use only gentle pressure when
cleaning the diffuser with a cotton swab or soft cloth to avoid scratching the outer surface. The solvent should be
allowed to do the cleaning, not mechanical force.
Never use abrasive material or cleaner on the diffuser.
Although Apogee sensors are very stable, nominal calibration drift is normal for all research-grade sensors. To
ensure maximum accuracy, recalibration every two years is recommended. Longer time periods between
recalibration may be warranted depending on tolerances. See the Apogee webpage for details regarding return of
sensors for recalibration (
http://www.apogeeinstruments.com/tech-support-recalibration-repairs/
To determine if your sensor needs recalibration, the Clear Sky Calculator (
) website
and/or smartphone app can be used to indicate the PPFD 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 light from clouds causes PPFD to increase
above the value predicted by the clear sky calculator. Measured values of PPFD can exceed values predicted by the
Clear Sky Calculator due to reflection from thin, high clouds and edges of clouds, which enhances incoming PPFD.
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 PPFD measurements to
calculated values for a clear sky. If sensor PPFD 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).
