Campbell Scientific Kipp and Zonen CMP-Series Pyranometers - Manual (Page 8)

CMP/CMA series manual
Page 7
This is important for an accurate measurement of the direct solar radiation. The diffuse solar radiation
is less influenced by obstructions near the horizon. For instance, an obstruction with an elevation of 5
o
over the whole azimuth range of 360
o
decreases the downward diffuse solar radiation by only 0.8%.
The radiometer should be readily accessible for cleaning the outer dome and inspecting the desiccant
It is evident that the radiometer should be located in such a way that a shadow will not be cast upon it
at any time (for example by masts or ventilation ducts). Note that hot exhaust gas (> 100
o
C) will
produce some radiation in the spectral range of the radiometer and cause an offset in the
measurements. The radiometer should be distant from light-coloured walls or other objects likely to
reflect sunlight onto it, or emitting short-wave radiation.
3. Mounting
The CMP pyranometer is provided with two holes for 5 mm bolts. Two each of stainless steel bolts,
washers, nuts and nylon insulation rings are provided in the fixing kit. The pyranometer should first be
secured lightly with the bolts to a solid and stable mounting stand or platform as shown in Figure 1.
After recalibration the nylon insulators must be replaced with new ones to prevent corrosion.
The mounting stand temperature can vary over a wider range than the air temperature. Temperature
fluctuations of the pyranometer body can produce offset signals, therefore it is recommended to isolate
the pyranometer thermally from the mounting stand by placing it on its levelling screws. Ensure that
there is a good electrical contact with earth to conduct away currents in the cable shield induced by
lightning.
Figure 1 Pyranometer installation
Note: After recalibration and/or reinstallation the nylon insulators must be replaced with new ones to
maintain durability.
4. Orientation
In principle no special orientation of the instrument is required, although the World Meteorological
Organisation (WMO) recommends that the signal lead is pointed towards the nearest pole, to minimise
heating of the electrical connections.