Kipp&Zonen CM 121 B/C Shadow Ring - Manual (Page 12)

3. PRINCIPLES & SPECIFICATIONS
Instruction manual CM 121 11
3. PRINCIPLES & SPECIFICATIONS
3.1 Theory
The objective of the shadow ring is to intercept the direct radiation coming to the pyranometer from
the sun during the whole day without readjustment. Therefore the shadow ring must satisfy the
following requirements. See also the schematic representation (fig. 2).
z
Once installed, the axis of the shadow ring must be always parallel to the polar-axis. In
consequence the angle between shadow ring axis and horizontal should be equal to the
latitude of the observation site.
z The shadow ring must be able to shift along the shadow ring axis relative to the pyranometer
and in this way be adjusted to the sun's changes in declination during the year.
z Within the shadow ring construction the pyranometer must be positioned with its sensor on
the shadow ring axis.
figure 2 schematic representation of the CM 121B on earth.
Also it is shown that the sliding bar setting is a function of the solar declination.