Campbell CM 21, Инструкция по эксплуатации

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for recalibration the use of the recalibration form in appendix VII is
recommended.
Accurate calibrations can also be done outdoors under clear conditions by
reference to a standard pyrheliometer. Many National Weather Services
have calibration facilities. Their standard pyrheliometer is compared with the
World Radiometric Reference (maintained at Davos, Switzerland) embodied
by several absolute pyrheliometers (black body cavity type).
The comparisons are indoors or at one of the regional Radiation Centres,
see Appendix III.
These institutes sometimes offer calibration facilities.
A summary of calibration methods is also found in the WMO guide
of 1996.
There are several procedures for transferring calibration from a narrow field
of view instrument (pyrheliometer) to a wide field of view instrument
(pyranometer). E.g. the direct component of the solar radiation is eliminated
temporarily from the pyranometer by shading the whole outer dome of the
instrument with a disk. There is however no thermal equilibrium with this
method and some pyranometer models show zero-offset drift.
There is another procedure, during which the unknown pyranometer remains
in its normal operating condition. This 'component' method involves
measuring the direct component with a pyrheliometer and the diffuse
component with a disk shaded pyranometer. As, during a clear day, the
diffuse radiance is only about 10% of the global radiation, the sensitivity of
the second pyranometer does not need to be known very accurately. Both
procedures are suitable to obtain a working standard pyranometer. The latter
is extensively described in International standard ISO 9846.
Transfer from the working standard pyranometer to other pyranometers can
be done in sunlight. The pyranometers must be mounted side by side so that
each views the same sky dome. It is desirable to integrate, or average, the
outputs over a period of time and then compute the calibration constants on
the basis of these averages. This reduces the errors due to changing
parameters during the day. See for detailed procedure International
Standard ISO 9847.