Delta-T Devices SunScan SS1 User Manual page 66

Checking the PAR calibration
Various techniques for checking the SunScan system PAR calibration and
consistency are described in Checking the probe/BF5 matching on
page 46, which you should refer to. This also includes advice on when to
use the recalibrate and restore factory calibration procedures.
Factory calibration method
A standard PAR Quantum sensor provides the reference value of PAR
that the Beam Fraction sensor and the SunScan probe are set up to. This
process is carried out under a near-daylight spectrum lamp in controlled
conditions.
Re-setting the factory calibration
The electronic components and photodiodes used in the PAR circuits of
the Beam Fraction sensor and SunScan probe are very stable and are not
expected to change for the lifetime of the instrument.
Circuit adjustment facilities in the Beam Fraction sensor are provided for
the initial factory set-up and are not intended to be used for routine
adjustment thereafter. The probe factory calibration cannot be adjusted
without specialist equipment.
Warning! Do not attempt to change the factory calibration without referring
back to Delta-T first.
The most likely cause of an apparent change of calibration is physical: dirt
or scratching on the BF5 dome, or dirt or staining on the SunScan diffuser.
To clean these use warm soapy water, or isopropyl Alcohol in the event of
very stubborn deposits.
If after checking the above you still have:

a Beam Fraction sensor with badly matched Total and Diffuse
outputs, or

a SunScan probe with an out-of-spec calibration, or individual diode
readings that appear faulty,
then please refer back to your distributor or the factory.
66  Technical Reference
SS1 User Manual v3.3