Campbell CNR1-L User Guide
CNR1 Net Radiometer
Revision: 8/09
Copyright © 2000-2009
Campbell Scientific, Inc.
Warranty and Assistance
The CNR1 NET RADIOMETER is warranted by CAMPBELL
SCIENTIFIC, INC. to be free from defects in materials and workmanship
under normal use and service for twelve (12) months from date of shipment
unless specified otherwise. Batteries have no warranty. CAMPBELL
SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or
replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
The customer shall assume all costs of removing, reinstalling, and shipping
defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL
SCIENTIFIC, INC. will return such products by surface carrier prepaid. This
warranty shall not apply to any CAMPBELL SCIENTIFIC, INC. products
which have been subjected to modification, misuse, neglect, accidents of
nature, or shipping damage. This warranty is in lieu of all other warranties,
expressed or implied, including warranties of merchantability or fitness for a
particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,
indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company
serves your country.
To obtain a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone (435) 753-2342. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container.
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CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784
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The form is available from our website at
completed form must be either emailed to repair@campbellsci.com
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www.campbellsci.com/repair
. A
or faxed to
CNR1 Table of Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. General Description.....................................................1
2. Sensor Specifications.................................................1
2.1 CNR1 Specifications ................................................................................1
2.2 CM3 Specifications ..................................................................................2
2.3 CG3 Specifications...................................................................................3
3. Installation....................................................................3
3.1 Connecting and Using the Heater.............................................................5
4. Using the CNR1 in the Four Separate
Components Mode (4SCM)....................................5
4.1 Measuring Solar Radiation with the CM3................................................5
4.2 Measuring Far Infrared Radiation with the CG3......................................6
4.3 Measuring the CNR1’s Temperature with the Pt-100 ..............................6
4.4 Calculation of the Albedo for Solar Radiation .........................................7
4.5 Calculation of the Net Solar Radiation (Net Short-Wave) .......................7
4.6 Calculation of the Net Infrared Radiation (Net Long-Wave)...................7
4.7 Calculation of the Net (total) Radiation....................................................8
5. Wiring............................................................................8
6. Datalogger Programming..........................................11
6.1 Calibration Factor...................................................................................12
6.2 Example Programs..................................................................................12
6.2.1 Example 1, CR1000 Using Differential Channels........................12
6.2.2 Example 2, CR5000 Using Differential Channels (no 4WPB100)14
6.2.3 Example 3, CR23X Program Using Differential Channels...........17
6.2.4 Example 4, CR23X Program Using Single-Ended Channels .......20
7. Calibration..................................................................22
8. Troubleshooting ........................................................23
8.1 Testing the CM3.....................................................................................23
8.2 Testing of the CG3 .................................................................................24
8.3 Testing the Pt-100...................................................................................24
i
CNR1 Table of Contents
A. CNR1 Performance and Measurements under
B. Using the Heater......................................................B-1
C. CR3000/CR5000 Program that Controls
Figures
Tables
Different Conditions...........................................A-1
B.1 General Information............................................................................ B-1
the Heater............................................................C-1
2-1. The Dimensions of the CNR1................................................................. 2
3-1. CNR1 Mounting Options........................................................................ 4
5-1. CNR1 Schematic. ................................................................................... 9
5-2. Interfacing the Pt-100 Using the 4WPB100 Module.............................. 9
6-1. 4WPB100 Module................................................................................ 12
5-1. Datalogger Connections for Differential Measurement, When Using
a 4WPB100 .......................................................................................10
5-2. Datalogger Connections for Single-Ended Measurement, When Using
a 4WPB100 .......................................................................................10
5-3. CR3000 and CR5000 Connections for Differential Measurement....... 11
A-1. Typical output signals of the CNR1 under different meteorological
conditions........................................................................................ A-2
ii
CNR1 Net Radiometer
1. General Description
The CNR1 Net Radiometer is intended for the analysis of the radiation balance
of Solar and Far Infrared radiation. The most common application is the
measurement of Net (total) Radiation at the earth's surface.
The CNR1 design is such that both the upward-facing and the downwardfacing instruments measure the energy that is received from the whole
hemisphere (180 degrees field of view). The output is expressed in Watts per
square meter. The total spectral range that is measured is roughly from 0.3 to
50 micrometers. This spectral range covers both the Solar Radiation, 0.3 to 3
micrometers, and the Far Infrared radiation, 5 to 50 micrometers.
The design of CNR1 is such that Solar radiation and Far Infrared radiation are
measured separately. Solar radiation is measured by two CM3 pyranometers,
one for measuring incoming solar radiation from the sky, and the other, which
faces downward, for measuring the reflected Solar radiation. From these two
pyranometers, albedo, the ratio of reflected and incoming radiation, can also be
determined. Far Infrared radiation is measured by two CG3 pyrgeometers, one
for measuring the Far Infrared radiation from the sky, the other from the soil
surface.
An incorporated heater allows the CNR1 to be heated to prevent dew or frost
accumulation on the sensors.
Additional information on the CNR1 sensor can be found in the Kipp & Zonen
CNR1 Manual. The primary intent of this manual is to provide information on
interfacing the CNR1 to Campbell Scientific dataloggers.
2. Sensor Specifications
2.1 CNR1 Specifications
See the Kipp & Zonen manual for additional specifications.
Sensor sensitivities: All four sensors have equal sensitivity
Pt-100 sensor temperature
measurement:
Expected accuracy of the
temperature measurement:
Operating temperature: -40 to +70 degrees Celsius
Requirements for data acquisition:
Radiation components:
Pt-100 temperature:
Expected accuracy for daily totals: ± 10 %
DIN class A
± 2 K, under non-stable conditions
with solar heating or heating by using
the heating resistor.
4 differential or 4 single-ended analog
channels
1 excitation and 2 differential analog
channels
1
CNR1 Net Radiometer
Cable length: 15 m (each cable)
Weight: 4 kg
Mounting arm attached to CNR1:
14.5” (37 cm) long
5/8” (1.6 cm) diameter
2
FIGURE 2-1. The Dimensions of the CNR1
2.2 CM3 Specifications
Specifications that are part of the ISO classification:
Response time 95%:
Non-stability:
Non-linearity:
Directional error:
Spectral selectivity:
Temperature dependence of
sensitivity:
18 s
< 1% change per year
Max. dev. 2.5% (0-1000 W m
Max. 25 W m
-2
at 1000 W m-2
Max. dev. 5% (350-1500 nm)
6% (-10 to +40
o
C)
-2
)
CNR1 Net Radiometer
Tilt response:
Overall ISO classification:
Sensitivity:
Impedance:
Operating temperature:
Spectral range:
Expected signal range for
atmospheric application:
Expected accuracy for daily sums:
Window heating offset:
2.3 CG3 Specifications
Response time 95%:
Non-stability:
Non-linearity:
Temperature dependence of
sensitivity:
Max. dev. 2%
second class
10 - 35 µV/(W m
-2
)
125 Ohm nominal
-40°C to +80°C
305-2800 nm (50% points)
0 - 15 mV typical
± 10%
Max. 25 W m
-2
at 1000 W m-2 normal
incidence solar radiation
18 s
< 1% change per year
Max. dev. 2.5% (0-1000 W m
6% (-10°C to +40°C)
-2
)
3. Installation
Tilt response:
Field of view:
Sensitivity:
Impedance:
Operating temperature:
Temperature range for specified
behavior:
Measurement range:
Spectral range:
Expected signal range for
atmospheric application:
Expected accuracy for daily sums:
Max. 3% when facing downwards
150 degrees
5 - 35 µV/(W m
-2
)
125 Ohm nominal
-40°C to +80°C
-10°C to +40°C
-250 to +250 W m
-2
5 to 50 µm
-4 to 4 mV
± 10%
For measurement of the Net Radiation, it is most important that the instrument
is located in a place that is representative of the entire region that one wishes to
study.
When installed on a mast, the preferred orientation should be such that no
shadow is cast on the Net Radiometer at any time during the day. In the
3
CNR1 Net Radiometer
Northern Hemisphere this implies that the Net Radiometer should be mounted
south of the mast.
It is suggested that the CNR1 is mounted at a height of at least 1.5 meters
above the surface to avoid shading effects of the instruments on the soil and to
promote spatial averaging of the measurement. If the instrument is H meters
above the surface, 99% of the input of the lower sensors comes from a circular
area with a radius of 10 H. Shadows or surface disturbances with radius
< 0.1 H will affect the measurement by less than 1%.
It is recommended that the CNR1 be mounted to a separate vertical pipe at
least 25’ from any other mounting structures. PN 14264 mounting bracket is
used to mount the CNR1 directly to a vertical pipe, or to a UT018 Tower
Mounting Bracket and Crossarm. Mount the sensor as follows:
1. Attach PN 14264 mounting bracket to the vertical mounting pipe or
UT018 crossarm using the hardware provided.
2. Insert the CNR1 mounting arm of the sensor into the 14264 mounting
block. Tighten the four set screws just enough to secure the mounting
arm position, but loose enough to allow the arm to be rotated.
NOTE
Do not attempt to rotate the instrument using the sensor heads or
you may damage the sensors; use the mounting arm only.
3. Loosen the vertical adjustment screws on the back of the 14264 mounting
bracket. Adjust the sensor mounting arm horizontally and vertically until
the bubble level on the sensor head shows level. Tighten the adjustment
screws to secure the position.
FIGURE 3-1. CNR1 Mounting Options
4
For installation in buildings or in solar energy applications, one will often have
to mount the CNR1 parallel to the surface that is being studied. This may be in
a tilted or a vertical position. The sensitivity of the radiometers will be
affected, but only in a minor way. This is specified as the so-called tilt effect.
From the specifications one can see that the tilt effect (this is a change in
sensitivity) remains within 3 %.
3.1 Connecting and Using the Heater
Only use the sensor’s heater when there is risk of dew forming on the sensors,
especially for low power installations. Furthermore, the heater should be
turned on and off infrequently because it may take some time for the sensor to
come to thermal equilibrium. No damage will result if the heater is powered
continuously, but as with all thermopile sensors, it is best if the sensor operates
at ambient temperatures and is not subject to rapid temperature changes.
The sensor power can be controlled using one of the 12V power switches built
into Campbell dataloggers or using an external solid state switch such as a
PSW12/SW12. The heater’s current drain is approximately 500 mA when
using a 12V battery. Connect the ground return from the heater either directly
to the battery or to a G terminal close the power input to the logger (i.e., not to
an analog ground near the measurement inputs).
CNR1 Net Radiometer
The heater power can be controlled by adding instructions to the datalogger
program that turns on the heater only when the light level falls below 20 W m
or, if a measurement of air humidity is available, when the dew point of the air
falls to within 1ºC of the sensor body temperature. More details about using
the heater are provided in Appendix B. Appendix C provides an example
CR3000/CR5000 program that controls the CNR1 heater.
4. Using the CNR1 in the Four Separate Components Mode (4SCM)
In the 4SCM configuration (measuring two Solar Radiation signals, two Far
Infrared signals and, for calculation purposes, one Pt-100 signal), all signals are
measured separately. Calculation of Net-Radiation and albedo can be done by
the datalogger, or later by the computer from the radiation and temperature
data.
The two CM3s will measure the solar radiation, both incoming and reflected.
The two CG3s will measure the Far Infrared radiation. For proper analysis of
the CG3 measurement results, they must be temperature corrected using the
temperature measurement performed by the Pt-100.
The following paragraphs describe how one should treat t h e instr ument, and
how different parameters like net Solar radiation, net Far Infrared radiation,
soil temperature, sky temperature, and Net (total) radiation can be calcul at e d.
-2
4.1 Measuring Solar Radiation with the CM3
Measuring with the upward-facing CM3 the so-called global (solar) radiation is
measured. The downward-facing CM3 measures the reflected solar radiation.
When calculating the Net radiation, the Reflected radiation must be subtracted
from the global radiation. See Section 4.5.
The CM3 pyranometer generates a mV signal that is simply proportional to the
incoming Solar radiation. The conversion factor between voltage, V, and
Watts per square meter of solar irradiance E, is the so-called calibration
constant C (or sensitivity).
For the CM3 E = V/C (4.1)
5
CNR1 Net Radiometer
4.2 Measuring Far Infrared Radiation with the CG3
The downward-facing CG3 measures the Far Infrared radiation that is emitted
by the ground. The upward-facing CG3 measures the Far Infrared radiation
from the sky. As the sky is typically colder than the instrument, one can expect
negative voltage signals from the upward-facing CG3. For this measurement,
the Pt-100 output is required. The Equation 4.2 is used to calculate the Far
Infrared irradiance of the sky and of the ground.
When using the CG3 pyrgeometer, one should realize that the signal that is
generated by the CG3 represents the exchange of Far Infrared (thermal)
radiation between the CG3 and the object that it is facing. This implies that the
CG3 will generate a positive voltage output, V, when it faces an object that is
hotter than its own sensor housing, and that it will give a negative voltage
signal when it faces an object that is colder. This means that for estimating the
Far Infrared radiation that is generated by the object that is faced by the
pyrgeometer, usually the sky or the soil, one will have to take the pyrgeometer
temperature, T, into account. This is why a Pt-100 is incorporated in the
CNR1's body. (This body is in very good thermal contact with the CG3 and
has the same temperature as the CG3 sensor surface.) The calculation of the
Far Infrared irradiance, E, is done according to the following equation:
-8
For the CG3 only E = V/C + 5.67 ⋅ 10
∗ T4 (4.2)
In this equation C is the sensitivity of the sensor. Please bear in mind that T is
in Kelvin, and not in Celsius or Fahrenheit.
4.3 Measuring the CNR1’s Temperature with the Pt-100
The Pt-100 temperature sensor is located in the CNR1 body. It will not
measure the exact temperature of the CG3 unless the whole instrument is in
thermal equilibrium. Errors, however, are minimized in the design by making
solid metal connections between the sensors and the temperature sensor. When
the sun is shining, the largest expected deviation between real sensor
temperature and Pt-100 reading is 2 degrees. This results in a worst-case error
for the CG3 of 10 Watts per square met e r.
The Pt-100 will not give a good indication of ambient air temperature; at 1000
Watts per square meter Solar radiation, and no wind, the instrument
temperature will rise approximately 12 degrees above ambient temperature.
The offsets of both pyranometers and pyrge ometers might be larger than 10
Watts per square meter if large temperature gradients are forced on the
instrument (larger than 5 K/hr). This happens, for example, when rain hits the
instrument. The occurrence of this can be detected using the Pt-100 readout. It
can be used as a tool for quality assurance of your data.
The 4WPB100 module is used to interface the Pt-100 to the datalogger, and is
included with the CNR1 sensor purchased from CSI. The 4WPB100
configures the Pt-100 as a 4-wire half bridge circuit that requires one excitation
and two differential channels on the datalogger (Section 5).
6
CNR1 Net Radiometer
4.4 Calculation of the Albedo for Solar Radiation
The albedo is the ratio of incoming and reflected Solar radiation. It is a figure
somewhere between 0 and 1. Typical values are 0.9 for snow, and 0.3 for
grassland. To determine albedo, the measured values of the two CM3s can be
used. The CG3s are not involved, as they do not measure Solar radiation. Do
not use measured values when solar elevation is lower than 10 degrees above
the horizon. Errors in measurement at these elevations are likely and thus
yielding unreliable results. This is due to deviations in the directional response
of the CM3s.
Albedo = (E lower CM3) / (E upper CM3) (4.3)
In the above formula, E is calculated according to Equation 4.1.
Albedo will always be smaller than 1. Checking this can be used as a tool for
quality assurance of your data. If you know the approximate albedo at your
site, the calculation of albedo can also serve as a tool for quality control of your
measured data at this specific site.
4.5 Calculation of the Net Solar Radiation (Net Short-Wave)
Net Solar radiation is equal to the incoming solar radiation minus the reflected
solar radiation.
Net Solar radiation = (E upper CM3) - (E lower CM3) (4.4)
In this formula E is calculated according to Equation 4.1.
Net Solar radiation will always be positive. Checking this can be used as a tool
for quality assurance of your measured data.
4.6 Calculation of the Net Infrared Radiation (Net Long-Wave)
Net Far Infrared radiation is, like Net Solar radiation, the part that contributes
to heating or cooling of the earth's surface. In practice, most of the time Net
Far Infrared radiation will be negative.
Net Far Infrared radiation = (E upper CG3) - (E lower CG3) (4.5)
In this formula E is calculated according to Equation 4.2. From this equation
the term with T cancels.
The E measured with the CG3 actually represents the irradiance of the sky (for
the upward- facing CG3) or the ground (for the downward-facing CG3).
Assuming that these two, ground and sky, behave like perfect blackbodies
(actually this is only in theory), one can calculate an effective "Sky
temperature" and an effective "Ground temperature".
Sky temperature
Ground Temperature
E upper CG3
⎡
=
⎢
567 10
.
⎣
⎡
=
⎢
⎣
14
/
⎤
⎥
−
8
⋅
⎦
E lower CG3
−
8
⋅
567 10
.
(4.6)
14
/
⎤
(4.7)
⎥
⎦
7
CNR1 Net Radiometer
As a rule of thumb, for ambient temperatures of about 20 degrees Celsius, one
can say that one degree of temperature difference between two objects results
in a 5 Watts per square meter exchange of radiative energy (infinite objects):
1 degree of temperature difference = 5 Watts per square meter (rule of thumb)
4.7 Calculation of the Net (total) Radiation
In the 4 Separate Components Mode, Net radiation, NR, can be calculated
using the individual sensor measurement results:
NR = (E upper CM3) + (E upper CG3) -
(E lower CM3) - (E lower CG3) (4.8)
Where E is the irradiance that is calculated for the CM3 according to Equation
4.1, for the CG3 according to Equation 4.2, the terms with T cancel from this
equation.
5. Wiring
Figure 5-1 shows the CNR1 schematic with the four radiation outputs, Pt-100
temperature sensor, and the heater. The use of the heater is described in detail
in the Appendix B. All wiring schemes shown in this manual will show wiring
for both CNR1 and 4WPB100 modules. Wiring diagrams and Tables 5-1 and
5-2 are applicable only if you bought the CNR1 Net Radiometer from
Campbell Scientific, Inc.
Use of the CNR1 Net Radiometer, which you bought outside of Campbell
Scientific, is possible only on the CR3000 and CR5000 dataloggers. The
PT-100 can connect directly to the CR3000 and CR5000 because they have
current excitation inputs. Table 5-3 and Program Example 6.2.4 show wiring
and programming on the CR5000 datalogger without the 4WPB module.
All other CSI dataloggers require the 4WPB100 module to interface the
PT-100 to the datalogger.
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