Kipp&Zonen CGR 4 User Manual
CGR 4
Pyrgeometer
Instruction Manual
IMPORTANT USER INFORMATION
Reading this entire manual is recommended for full understanding of the use of this
product.
Should you have any comments on this manual we will be pleased to receive them at:
Kipp & Zonen B.V.
Delftechpark 36, 2628 XH Delft
P.O. Box 507, 2600 AM Delft
The Netherlands
T: +31 (0) 15 2755 210
F: +31 (0) 15 2620 351
info@kippzonen.com
www.kippzonen.com
Kipp & Zonen reserves the right to make changes to the specifications without prior
notice.
WARRANTY AND LIABILITY
Kipp & Zonen guarantees that the product delivered has been thoroughly tested to
ensure that it meets its published specifications. The warranty included in the conditions
of delivery is valid only if the product has been installed and used according to the
instructions supplied by Kipp & Zonen.
Kipp & Zonen shall in no event be liable for incidental or consequential damages,
including without limitation, lost profits, loss of income, loss of business opportunities,
loss of use and other related exposures, however used, rising from the faulty and
incorrect use of the product. User made modifications can affect the validity of the CE
declaration.
COPYRIGHT© 2014 KIPP & ZONEN
All rights are reserved. No part of this publication may be reproduced, stored in a
retrieval system or transmitted in any form or by any means, without permission in
written form from the company.
Manual version: V1401
Page 2
Declaration of Conformity
According to EC guideline 89/336/EEC 73/23/EEC
We Kipp & Zonen B.V.
Delftechpark 36, 2628 XH Delft
P.O. Box 507, 2600 AM Delft
The Netherlands
Declare under our sole responsibility that the products
Type: CGR 3 / CGR 4
Name: Pyrgeometer
to which this declaration relates are in conformity with the following standards
Imissions EN 50082-1 Group standard
Emissions EN 50081-1 Group standard
EN 55022
Safety standard IEC 1010-1
Following the provisions of the directive.
B.A.H. Dieterink
President
KIPP & ZONEN B.V.
Page 3
Table of contents
IMPORTANT USER INFORMTION
Declaration of Conformity
Table of contents
1. Introduction
2. Installation and operation
2.1. Delivery
2.2. Mechanical installation
2.2.1. Installation for measurement of long-wave downward radiation
2.2.2. Installation for measurement of radiation on inclined surfaces
2.2.3. Installation for measurement of upward long-wave radiation
2.2.4. Installation for shaded measurement of downward long-wave radiation
2.2.5. Installation for measurement of net long-wave radiation
2.3. Electrical installation
2.4. Operation
2.4.1. Overcast sky
2.4.2. Clear sky
2.4.3. Measurements during a sunny day
2.5. Measurement uncertainty
2.6. Maintenance
3. Principle components of pyrgeometers
3.1. Window
3.2. Detector
3.3. Temperature sensor
3.4. Housing
3.5. Drying cartridge
3.6. Cable and connector
4. Pyrgeometer physical properties
4.1. Spectral range
4.2. Sensitivity
4.3. Impedance
4.4. Response time
4.5. Non-linearity
4.6. Temperature dependence
4.7. Tilt error
4.8. Window heating offset
4.9. Zero offset B due to ambient temperature changes
4.10. Operating temperature
4.11. Field of view
4.12. Directional response
4.13. Maximum irradiance
4.14. Non-stability
4.15. Spectral selectivity
4.16. Environmental
4.17. Uncertainty
5. Calibration
5.1. Calibration principle
5.2. Calibration procedure at Kipp & Zonen
5.3. Traceability to World Radiometric Reference
5.4. Recalibration
6. CGR models
6.1. CGR 4
6.2. CGR 4 performance specifications
6.3. CGR 4 general specifications
7. Frequently asked questions
8. Trouble shooting
Appendix I Radiometric terminology
Appendix II 10k thermistor specifications
Appendix III Pt-100 specifications
Appendix IV List of World and Regional Radiation Centres
Appendix V Recalibration service
...........................................................................................................................
........................................................................................................................
............................................................................................................................
..........................................................................................................................
......................................................................................................................
...........................................................................................................................
.....................................................................................................................
.............................................................................................................................
............................................................................................................................
............................................................................................................................
...................................................................................................................
.........................................................................................................................
........................................................................................................................
...................................................................................................................
.....................................................................................................................
...........................................................................................................................
......................................................................................................................
......................................................................................................................
...................................................................................................................
........................................................................................................................
...........................................................................................................................
.....................................................................................................................
..........................................................................................................................
................................................................................................................................
..................................................................................................................
......................................................................................................
...............................................................................................................
....................................................................................................
......................................................................................................
........................................
..........................................
............................................
...................................................
........................................................................................................
......................................................................................
...................................................................................................
.................................................................................
...........................................................................................................
................................................................................................................
..........................................................................................................
..........................................................................................
...................................................................................................
.......................................................................................................
..............................................................
.......................................................................................................
..........................................................................................................
..........................................................................................................
.............................................................................................................
..........................................................................................................
................................................................................
.......................................................................
.......................................................................................
...............................................................................................
..................................................................................................
...............................................................................................
.......................................................................................
..................................................................................................
...............................................................
...................................................................................................
............................
2
3
4
5
6
6
6
6
8
8
9
9
10
11
12
12
13
13
15
16
16
17
17
18
18
18
19
19
20
20
20
20
20
20
21
21
22
22
22
22
22
22
23
23
24
24
24
24
24
25
25
26
27
28
29
30
31
32
33
34
Page 4
CGR 4 Manual
1. Introduction
Dear customer, thank you for purchasing a Kipp & Zonen instrument. Please read this manual and the
separate instruction sheet for a full understanding of the use of your pyrgeometer.
A CGR series pyrgeometer is a high quality radiometer designed for measuring long-wave irradiance on
a plane surface (radiant flux, W/m2) which results from radiation incident from the hemisphere above the
instrument.
According to the World Meteorological Organisation (WMO) a pyrgeometer is the designated type of
instrument for the measurement long-wave atmospheric radiation.
This manual, together with the instruction sheet, gives information related to installation, maintenance,
calibration, product specifications and applications of the CGR series. Note that the smaller CGR 3
pyrgeometer with a flat infrared window is largely excluded from this manual due to the different
construction. However, the general definitions and principles also apply to this model.
If any questions should remain, please feel free to contact your Kipp & Zonen dealer or e-mail
info@kippzonen.com
For information about other Kipp & Zonen products or to check for any update of this manual, go to
www.kippzonen.com
Page 5CGR 4 Manual
2. Installation and operation
2.1. Delivery
Check the contents of the shipment for completeness (see below) and note whether any damage has
occurred during transport. If there is damage, a claim should be filed with the carrier immediately. In
this case, or if the contents are incomplete, your dealer should be notified in order to facilitate the repair
or replacement of the instrument.
Contents of delivery:
1. Radiometer
2. Sun shield
3. Cable with connector
4. Test reports
5. Instruction sheet
6. Radiometer fixing kit
7. 2x Desiccant bags
8. Product documentation CD
Although all CGR radiometers are weatherproof and suitable for harsh environmental conditions, they
have some delicate mechanical parts. Please keep the original packaging for safe transport of the
radiometer to the measurement site or for use when returning the radiometer for calibration.
The calibration certificate supplied with the instrument is valid for 1 year from the date of first use by the
customer, subject to the variations in performance due to specific operating conditions that are given in
the instrument specifications. The calibration certificate is dated relative to the time of manufacture, or
recalibration, but the instrument does not undergo any sensitivity changes when kept in the original
packing and not exposed to light. From the moment the instrument is taken from its packaging and
exposed to irradiance the sensitivity will deviate slightly with time. See the 'non-stability' performance
(maximum sensitivity change per year) given in the radiometer specification list.
2.2. Mechanical installation
The mechanical installation of the radiometer depends upon the measuring purpose. Different measuring
methods will be explained in the next paragraphs.
2.2.1. Installation for measurement of long-wave downward radiation
The following steps must be carefully taken for optimal performance of the instrument.
1. Desiccant
Check the condition of the desiccant and replace if necessary, for example after a long storage period.
2. Location
Ideally the site for the pyrgeometer should be free from any obstructions to the horizon above the plane
of the sensing element. If this is not possible, the site should be chosen in such a way that any obstruction
over the azimuth range should have an elevation not exceeding 10°. In particular, no sources of heat
(such as ventilation / heating outlets) should be within the field of view.
Page 6 CGR 4 Manual
3. Mounting
The CGR pyrgeometer 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 pyrgeometer 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 pyrgeometer body can produce offset signals, therefore it is recommended to isolate
the pyrgeometer 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: Pyrgeometer 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.
5. Level pyrgeometer
Accurate measurement of the global radiation requires proper levelling of the thermopile surface. Level
the instrument by turning the two levelling screws to bring the bubble of the spirit level centrally within
the marked ring. For easy levelling, first use the screw nearest to the spirit level. When the pyrgeometer
is placed horizontally using the bubble level, or when it is mounted with its base directly on a horizontal
plane, the thermopile is horizontal within 0.1°.
Page 7CGR 4 Manual
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 offset 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.
Figure 2: Upward long-wave radiation
Page 8 CGR 4 Manual
2.2.4. Installation for shaded measurement of downward long-wave radiation
For measuring atmospheric radiation with some pyrgeometers,
such as the CGR 3, it is desirable to shield the instrument from
the direct short-wave solar radiation which may heat up the
pyrgeometer dome or window and cause significant thermal
offsets. The direct solar radiation is intercepted by a small disk or
sphere. The shadow of the disk must cover the pyrgeometer dome
completely. However, to follow the sun's apparent motion, a
power-driven tracking device is necessary.
This can be done using a Kipp & Zonen sun tracker, such as the
model 2AP, designed to track the sun accurately under all
weather conditions. More information about the combination of
pyrgeometer and tracker is given in the sun tracker manual.
Alternatively, a static shadow ring can be used to intercept the direct solar radiation; but it is less
accurate and may require periodic manual adjustment. At times the shadow ring also intercepts a
proportion of the diffuse sky radiation. Therefore, corrections for this to the recorded data are necessary.
Kipp & Zonen produces a universal shadow ring, model CM 121, which is suitable for use at all latitudes.
In the CM 121 manual, installation instructions and correction factors are given.
In practice the CGR 4 does not require shading from direct short-wave solar radiation because the
dome-heating effect, when suitably ventilated, is negligible due to the unique construction of the
pyrgeometer.
Figure 3: 2AP Sun Tracker with
shaded pyrgeometer
2.2.5. Installation for measurement of net long-wave radiation
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 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.
The requirements for installation of the upper and lower
pyrgeometers are the same as in paragraphs 2.2.1 and 2.2.3 for
downward and upward long-wave radiation.
A typical arrangement is shown in Figure 4. According to the
WMO the height should be 1 m to 2 m above a uniform surface
covered by short grass.
The mast shown intercepts a fraction D/2πS of the radiation that
is coming from the ground. In the most unfavourable situation
(sun at zenith) the pyrgeometer shadow decreases the signal by a
factor R²/H².
When determining the net long-wave radiation, it is not strictly
necessary to record the pyrgeometer housing temperatures.
Assuming that the temperatures of the upper and lower housings
are equal, it can be cancelled from the equation for net-radiation.
Figure 4: Net radiation configuration
CGR 4 Manual
Page 9
However, if the upward and downward radiation components are to be measured separately it is necessary
to record the individual housing temperatures to calculate the radiation values.
Using the combination of a net pyrgeometer (two CGR 3 or CGR 4 instruments) and a CMA 6 or CMA 11
albedometer the net total radiation (energy balance) can be calculated with high accuracy from thefour
component values. Problems with dew deposition, frost, etc, can be minimised by using the Kipp &
Zonen CV 2 ventilation unit with optional heating.
This has many advantages over conventional net total radiation sensors with plastic (polyethylene)
windows. These cannot provide individual short and long-wave radiation values and cannot separate
upward and downward contributions. The soft plastic domes do not fully protect the sensor from the
thermal effects of wind and rain, are easily soiled, are difficult to clean and require regular replacement.
2.3. Electrical installation
As standard the CGR is supplied with a waterproof connector pre-wired to 10 m cable with a number of
leads and a shield covered with a black sleeve. The number of connector pins and cable leads depends
upon the type of temperature sensor that is fitted. The colour code of the wires and the connector pin
numbers are shown on the instruction sheet. Longer cables are available as options.
Preferably, secure the pyrgeometer with its levelling screws or mounting rod to a metal support with a
good connection to earth (e.g. by using a lightning conductor).
The shield of the cable is connected to the aluminium radiometer housing through the connector body.
The shield at the cable end may be connected to ground at the readout equipment. Lightning can induce
high voltages in the shield but these will be led off at the pyrgeometer and data logger.
Kipp & Zonen pyrgeometer cables are of low noise type, but bending the cable produces small voltage
spikes, a tribo-electric and capacitance effect. Therefore, the cable must be firmly secured to minimise
spurious responses during stormy weather.
The impedance of the readout equipment loads the temperature compensation circuit and the thermopile.
It can increase the temperature dependency of the pyrgeometer. The sensitivity is affected more than 0.1%
when the load resistance is less than 100 kΩ. For this reason we recommend the use of readout equipment
with an input impedance of 1 MΩ or more. The solar integrators, data loggers and chart recorders from
Kipp & Zonen meet these requirements.
Long cables may be used, but the cable resistance must be smaller than 0.1% of the impedance of the
readout equipment. It is evident that the use of attenuator circuits to modify the calibration factor is not
recommended because the temperature response will also be affected.
A high input bias current at the readout equipment can produce several micro-Volts across the impedance
of the pyrgeometer and cable. The zero offset can be verified by replacing the pyrgeometer impedance at
the readout equipment input terminals with a resistor.
The pyrgeometer can also be connected to a computer or data acquisition system. A low voltage analogue
input must be available. The resolution of the Analogue-to-Digital Converter (ADC) must allow a system
sensitivity of about 1 bit per W/m². More resolution is not necessary during outdoor measurements,
because even the best pyrgeometer (the CGR 4) exhibits offsets greater than 2 W/m² due to lack of
thermal equilibrium.
Page 10 CGR 4 Manual
2.2.4. Installation for shaded measurement of downward long-wave radiation
For amplification of the pyrgeometer signal Kipp & Zonen offers the AMPBOX signal amplifier.
This amplifier will convert the micro-Volt output from the pyrgeometer into a standard 4 – 20 mA signal.
The use of the AMPBOX amplifier is recommended for applications with long cables (> 100m), electrically
noisy environments or data loggers with a current-loop input.
The AMPBOX can be factory adjusted to suit the sensitivity of an individual pyrgeometer to produce a
defined range, typically 4 mA represents -300 W/m², 16 mA represents 0 W/m2 and 20 mA represents
+100 W/m².
2.4. Operation
After completing the installation the pyrgeometer will be ready for operation. The downward atmospheric
long-wave radiation can be calculated with Formula 1 by measuring the detector output voltage Uemf [µV],
the housing temperature T
[K], and taking the sensitivity calibration factor S [µV/W/m²] into account.
b
U
emf
Formula 1
Ld=
=Downward atmospheric long-wave radiation [W/m²]
L
d
=Net radiation (difference between the downward [W/m²]
U
emf
longwave radiation emitted from the atmosphere
S
and the upward irradiance of the CGR 4 detector)
=Upward irradiance of the CGR 4 detector [W/m²]
5.67 • 10
Note that the net radiation term (U
long-wave radiation is smaller than the detector’s upward irradiance ( ).
This refers to the net radiation within the pyrgeometer, not the ‘net radiation’ as referred to in 2.2.5.
In the Baseline Surface Radiation Network (BSRN) manual (WMO/TD-No.897) an extended formula is
described. This formula corrects for window heating and so called “solar radiation leakage”. Due to the
very low window heating offset and optimal spectral cut-on wavelength, these corrections are not
necessary for the CGR 4.
To be certain that the quality of the data is of a high standard, care must be taken with daily maintenance
of the pyrgeometer. Once a voltage measurement is taken, nothing can be done to retrospectively
improve the quality of that measurement.
S
+
5.67 • 10
4
-8
• T
b
4
-8
• T
b
/ S) is mostly negative, so the calculated downward atmospheric
emf
5.67 • 10
4
-8
• T
b
During field measurements the pyrgeometer is exposed to varying atmospheric conditions with typical
radiating properties. Therefore we define the two most common conditions as ‘overcast sky’ and ‘clear
sky’, refer to 2.4.1 and 2.4.2 respectively.
CGR 4 Manual
Page 11
Loading...