Kipp&Zonen CGR 4 Pyrgeometers - Manual (Page 25)

6. CGR models
The CGR series comprises 2 models, CGR 3 and CGR 4. The mechanical construction of the CGR 3 differs
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 offset 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 effect.
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 effectively, by a
unique construction. Even in full sunlight the window heating offset 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 offset.
- 180° field of view with good cosine response.
- Diamond-like coating for optimal protection against environmental influences.
- Low temperature dependence of sensitivity.
Page 25 CGR 4 Manual