Calibration Procedure At Kipp & Zonen; The Facility; Procedure - Kipp & Zonen CM 11 Instruction Manual

CALIBRATION
A summary of calibration methods is also found in the WMO guide
of 1996.
To send a pyranometer back for recalibration the use of the recalibration form
in appendix V is strongly recommended.
6.3 CALIBRATION PROCEDURE AT KIPP & ZONEN

6.3.1 The facility

The indoor calibration procedure is based on a side-by-side comparison with a
reference pyranometer under an artificial sun fed by an AC voltage stabiliser.
It embodies a 150 W Metal-Halide high-pressure gas discharge lamp. Behind
the lamp is a reflector with a diameter of 16.2 cm. The reflector is 110 cm
above the pyranometers producing a vertical beam. The irradiance at the
pyranometers is approximately 500 W/m²
To minimise stray light from the walls and the operator, the light is limited to a
small cone around the two pyranometers. The unknown pyranometer 'a' and
the standard pyranometer 'b' are placed side by side on a small table. The
table can rotate to interchange the positions (1 and 2) of the pyranometers.
The lamp is centred on the rotating axis of this table. Actually there is no
normal incidence of the radiation, but the angle of incidence is the same for
both pyranometers (3°) so this cannot give rise to errors. The two
pyranometers are not levelled with the screws, but placed on their bases. The
effect of a small tilt is almost zero (Compare cos. 3° = 0.9986 and cos. 4° =
0.9976).

6.3.2 Procedure

After illuminating for 60 s, the output voltages of both pyranometers are
integrated over 30 s with a solar integrator. Next, both pyranometers are
covered by a blackened 'hat'. After 60 s the zero offset signal of both
pyranometers is integrated again.
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