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6. Secure pyrgeometer
Secure the pyrgeometer tightly with the two stainless steel bolts. Ensure that the pyrgeometer maintains
the correct levelled position!
7. Fit cable and sun shield
Locate the cable plug correctly in the radiometer socket (it only fits one way) and screw the plug locking
ring hand-tight. Finally, clip on the sun shield to prevent excessive heating of the radiometer body.
The bubble level is visible through the top of the sun shield for routine checks.
2.2.2. Installation for measurement of radiation on inclined surfaces
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 10°C above air temperature), the housing must be thermally isolated
by the levelling screws from the stand. This will promote a thermal equilibrium between the dome and
the housing and decrease zero o set signals.
2.2.3. Installation for measurement of upward long-wave radiation
In the inverted position the pyrgeometer measures radiation from the ground. According to the WMO the
height should be 1 m to 2 m above a uniform surface covered by short grass.
The mounting device should not interfere
significantly with the field of view of the
instrument. The upper plate prevents excessive
heating of the pyrgeometer body by solar
radiation and, if large enough, it keeps the
lower screen free of precipitation. The lower
glare screen prevents direct illumination of the
dome by the sun at sunrise and sunset and is
available as an accessory kit for the CGR series.
The mast shown in Figure 2 intercepts a
fraction D/2πS of the radiation coming from
the ground. In the most unfavourable
situation (sun at zenith) the pyrgeometer
shadow decreases the signal by a factor R²/H².
A rule of thumb is:
A black shadow with radius = 0.1 H on the field
below decreases the signal by 1% and 99% of
the signal will originate from an area with
radius 10 H.
Page 8
Figure 2: Upward long-wave radiation
CGR 4 Manual
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