Kipp&Zonen CM 121 B/C Shadow Ring - Manual (Page 15)

4. MOUNTING AND ALIGNMENT
Instruction manual CM 121 14
4. MOUNTING AND ALIGNMENT
4.1 Introduction
The CM 121B can be mounted on any surface that is within one degree horizontal. It can also be
mounted on a tilted plane, if that plane faces south or north within 1/4 degree.
As explained in the previous chapter, the CM 121B has to be aligned north-south and the sliding
bars must be tilted and brought parallel to the polar axis. These two steps are described below.
Please mind that it is necessary to perform the north south alignment before the tilting of the sliding
bars, because it might be necessary to change the tilting during the north south alignment.
4.2 North-south alignment (one time installation)
The shadow ring has to be aligned to the north south axis. The preferred method to set the orienta-
tion is by observing the sun at 12.00 True Solar Time (= Local Apparent Time). This is the moment
when the sun is exactly south or north, a quite different time than 12.00 local clock or civil time. The
True Solar Time can be obtained from an astronomic observatory or taking the time in between
sunrise and sunset from the newspaper. For orienting the CM 121B at the sun, there is a groove
made in two separate metal sections of the sector. The sector can be oriented such that this groove
is aimed at the sun. The groove can be used as a sight (see fig.4). When the solar beam that
passes the first groove can also pass the second groove, the CM 121 is supposed to be aligned
with the sun. It is realized that close to the equator, this method looses its validity, and one has to
rely more on geographic orientation.
Caution:
Please mind that for proper positioning of the pyranometer relative to the ring, the sector
is supposed to be fixed with its lower curved surface in direct contact with the upper
curved surface of the pyranometer support.
z
Wait for a moment that the sun is shining.
z Direct the CM 121B roughly north-south using a map or compass. If possible it can be
recommended to use the sight for optimal orientation. Please note that if the sliding bar angle
is approximately correct (see next paragraph), the highest point of the ring should be pointing
south if the site is on the northern hemisphere, it should be pointing north if the site is in the
southern hemisphere. (see figure 4). Please note that close to the equator the orientation by
compass and subsequent correction by looking at sunrise and sunset performance can be
preferred.
z Now start the real alignment procedure:
z Unscrew the fixing screws of the sliding bars
z Put the shadow ring in a low position so that the sector is not shaded.
z Set the base of the CM 121B horizontal using a level. Do not fasten it.
z Loosen the pyranometer sector so that it can be rotated, changing its tilt angle, loosen the
securing bolt of the crossbar.
z Wait for solar noon.
z At solar noon, aim the sight on the pyranometer support exactly at the sun, keeping the
CM 121B base in the horizontal position, if necessary turning the CM 121B around its pillar
axis, turning the pyranometer sector and the crossbar in the north-south plane, changing its
tilt angle. The sight for doing the exact positioning consists of two grooves in the sector (see
above or fig.4).
z Rotate the sector and the whole CM 121 until the sights coincide with the centre of the sun
disc at 12.00 True Solar Time. Mind that the sun disc is moving 1/4 degree per minute along
the sky. The sun disc itself subtends half a degree.
z Fix the shadow ring base
z Install the pyranometer. Please note that installation of the pyranometer requires removal of
the levelling screws of the pyranometer. One can let the fixed foot stay on the pyranometer.
z Please mind that for proper positioning of the pyranometer relative to the ring, the sector is
supposed to be fixed with its lower curved surface in direct contact with the upper curved
surface of the pyranometer support.
z Perform the procedure for tilting of the sliding bars (paragraph 4.3)
z Elevate the shadow ring along the sliding bars so that it shades the pyranometer sensor
z Check if the elevation is conforming the sliding bar scale pointer as indicated in the table