Advertisement
6. CGR models
The CGR series comprises 2 models, CGR 3 and CGR 4. The mechanical construction of the CGR 3 di ers
from the CGR 4 in that it has a flat silicon window, smaller housing dimensions and no drying cartridge
(the housing is completely sealed). Features and specifications of the CGR 4 pyrgeometers are given in
this chapter. The CGR series is designed for measuring the downward radiation (W/m²) on a plane
surface from the atmosphere above.
CGR 4 pyrgeometer includes an integrated bubble level, refillable drying cartridge, white snap-on sun
shield, and a shielded signal output cable with connector.
CGR 4 can be used in conjunction with the Kipp & Zonen CV 2 ventilation unit for enhanced measurement
performance and overall reduced instrument maintenance.
For reducing the window heating o set error, the direct solar radiation can be shielded statically from
the CGR 3 pyrgeometer by the Kipp & Zonen shadow ring CM 121, and fully automatically by the 2 AP Sun
Tracker with shading system. This can also be done for the CGR 4 but is not really necessary because of
the minimal window heating e ect.
A net pyrgeometer measures both the downward atmospheric long-wave radiation and the upward
long-wave radiation from the surface below. It can be configured from two CGR 4 series pyrgeometers
and a suitable mounting plate. In the case of the CGR 3, two instruments can be simply mounted
back-to-back and an optional mounting rod fitted.
6.1. CGR 4
CGR 4 has been designed for scientific measurements outdoors of downward atmospheric long-wave
radiation with extremely high reliability and accuracy.
CGR 4 provides an output voltage that is proportional to the net radiation in the far infrared (FIR). By
calculation, downward atmospheric long-wave radiation is derived. CGR 4 has an integrated temperature
sensor to measure the housing temperature.
CGR 4 uses a specially designed silicon meniscus dome. Although the window is not hemispherical, CGR 4
has a 180° field of view with good cosine response. A hard-carbon, diamond-like, coating protects the
outer surface of the window and smoothes the spectral response. On the inside, a solar blind interference
filter blocks all short-wave solar radiation.
The solar radiation absorbed by the window is conducted away into the housing very e ectively, by a
unique construction. Even in full sunlight the window heating o set is very low compared to that of other
pyrgeometers on the market. This allows accurate daytime measurements without the need for a tracking
shading disk. It also eliminates the need for window heating compensation by using the correction
formula.
The special features of the CGR 4 are:
-
Sensitive to infrared radiation in a wavelength range from 4.5 to 42 µm.
-
Extremely low window heating o set.
-
180° field of view with good cosine response.
-
Diamond-like coating for optimal protection against environmental influences.
-
Low temperature dependence of sensitivity.
CGR 4 Manual
Page 25
Advertisement
