Campbell CM 21, Инструкция по эксплуатации

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3. Levelling
Accurate measurement of the global radiation requires proper levelling of the
thermopile surface. Level the instrument by turning the levelling screws to
bring the bubble of the spirit level within the marked ring.
For easy levelling first use the screw nearest to the spirit level.
When the CM 21 is placed horizontally using the spirit level, or when it is
mounted with its base on a horizontal plane, the thermopile is horizontal
within 0.05º. This causes an extra azimuthal variation of + or - 0.5% at a
solar elevation of 10º. By radiometrically levelling, the pyranometer can be
placed more accurately horizontal (See Appendix II).
Finally, the pyranometer should be secured tight with the two stainless steel
bolts. Ensure that the pyranometer maintains the correct levelled position!
3.2.2 Installation for measurement of solar radiation on
inclined surfaces
See also 'installation for measurement of global radiation'.
It is advised to pre-adjust the levelling screws on a horizontal surface for
easy orientation of the instrument parallel to the inclined surface. Because
the temperature of the mounting stand is expected to rise considerably
(more than 10ºC above air temperature), the body must be thermally isolated
by the levelling screws from the stand. This will promote a thermal
equilibrium between domes and body and decrease zero offset signals.
The CM 21 pyranometer shows no significant tilt effect up to irradiances of
1000 W/m
2
.
3. INSTALLATION