Campbell CNR4 User manual

Revision: 06/2021
Copyright © 2000 – 2021
Campbell Scientific, Inc.

Table of contents
1. Introduction 1
2. Precautions 1
3. Initial inspection 1
3.1 Ships with 1
4. QuickStart 2
5. Overview 5
6. Specifications 6
6.1 CNR4 specifications 7
6.2 Pyranometer specifications 8
6.3 Pyrgeometer specifications 9
6.4 Optional CNF4 heater/ventilator 10
6.4.1 CNF4 specifications 10
7. Installation 10
7.1 Siting considerations 11
7.2 Mounting 11
7.3 Wiring 13
7.4 Data logger programming 17
7.4.1 Sensor sensitivity 18
7.4.2 Internal temperature sensors programming 18
8. Operation 19
8.1 Short-wave solar radiation measurements 19
8.2 Long-wave far infrared radiation measurements 20
8.3 Internal temperature sensors measurements 21
8.4 Calculation of albedo 24
8.5 Calculation of net short-wave radiation 24
8.6 Calculation of net long-wave radiation 25
8.7 Calculation of net (total) radiation 25
9. Troubleshooting and maintenance 26
9.1 Troubleshooting 26
Table of Contents - i

9.1.1 Testing the pyranometer 26
9.1.2 Testing the pyrgeometer 27
9.1.3 Testing the thermistor 27
9.1.4 Testing the Pt-100 28
9.2 Maintenance 28
9.2.1 Cleaning windows and domes 28
9.2.2 Replacing the drying cartridge 28
9.3 Recalibration 29
Appendix A. Importing Short Cut code into CRBasic Editor 30
Appendix B. CNR4 performance and measurements under different conditions 31
Appendix C. CNF4 heater ventilator 35
C.1 General information 35
C.2 Attaching the optional CNF4 heater/ventilator unit to CNR4 37
C.3 Wiring 41
C.4 Data logger programming for heater/ventilator control 43
C.5 CNF4 heater/ventilator maintenance 43
C.5.1 Testing the heater 43
C.5.2 Testing the ventilator 43
C.5.3 Replacing the filter for the ventilator 44
Table of Contents - ii

1. Introduction
The CNR4 is a research-grade net radiometer that measures the energy balance between
incoming and outgoing radiation. Our data loggers measure the CNR4 output. This net
radiometer offers a professional solution for scientific-grade energy balance studies.
2. Precautions
lREAD AND UNDERSTAND the Safety section at the back of this manual.
lAlthough the CNR4 is rugged, it is also a highly precise scientific instrument and should be
handled as such.
lCare should be taken when opening the shipping package to not damage or cut the cable
jacket. If damage to the cable is suspected, contact Campbell Scientific.
lDo not attempt to rotate the instrument using the sensor heads, or you may damage the
sensors; use the mounting rod only.
3. Initial inspection
lUpon receipt of the CNR4, inspect the packaging and contents for damage. File damage
claims with the shipping company.
lThe model number and cable length are printed on a label at the connection end of the
cable. Check this information against the shipping documents to ensure the correct
product and cable length are received.
lRefer to the Ships with list to ensure that parts are included (see Ships with (p. 1)).
3.1 Ships with
(2) Drying Cartridges
(1) WRR Traceable Calibration Certificate for the pyranometers
(1) WRR Traceable Calibration Certificate for the pyregeometers
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(1) Mounting Arm from original manufacturer
(1) Extra Calibration Stickers from original manufacturer
4. QuickStart
NOTE:
The Short Cut example provided here uses the thermistor to provide the temperature
correction.
A video that describes data logger programming using Short Cut is available at:
www.campbellsci.com/videos/cr1000x-datalogger-getting-started-program-part-3 . Short Cut
is an easy way to program your data logger to measure the sensor and assign data logger wiring
terminals. Short Cut is available as a download on www.campbellsci.com . It is included in
installations of LoggerNet, RTDAQ, or PC400.
The following procedure also describes programming with Short Cut.
1. Open Short Cut and click Create New Program.
2. Double-click the data logger model.
3. In the Available Sensors and Devices box, type CNR4 or locate the sensor in the Sensors >
Meteorological > Solar Radiation folder. Double-click CNR4 Net Radiation. Type the
sensitivity values supplied on the manufacturer certificate of calibration; these sensitivity
values are unique to each sensor.
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4. Click on the Wiring tab to see how the sensor is to be wired to the data logger. Click OK
after wiring the sensor.
5. Repeat steps three and four for other sensors. Click Next.
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6. In Output Setup, enter the scan rate, Data Output Storage Intervals, and meaningful table
names.
7. Select the measurement and its associated output options.
8. Click Finish and save the program. Send the program to the data logger if the data logger
is connected to the computer.
9. If the sensor is connected to the data logger, check the output of the sensor in the data
logger support software data display in LoggerNet, RTDAQ, or PC400 to make sure it is
making reasonable measurements.
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5. Overview
The CNR4 Net Radiometer consists of a pyranometer pair, one facing upward, the other facing
downward, and a pyrgeometer pair in a similar configuration. The pyranometer pair measures
short-wave solar radiation, and the pyrgeometer pair measures long-wave far infrared radiation.
The upper long-wave detector of CNR4 has a meniscus dome to ensure that water droplets roll
off easily while improving the field of view to nearly 180°, compared with a 150° for a flat window.
All four sensors are integrated directly into the instrument body, instead of separate modules
mounted onto the housing. Each sensor is calibrated individually for optimal accuracy.
Two temperature sensors, a thermistor and a Pt-100, are integrated with the CNR4 body. The
temperature sensor is used to provide information to correct the infrared readings for the
temperature of the instrument housing. Care has been taken to place the long-wave sensors
close to each other and close to the temperature sensors. This ensures that the temperatures of
the measurement surfaces are the same and accurately known, improving the quality of the
long-wave measurements. A completion resistor is added in the pig tail end of the thermistor
cable providing an easy interface with data loggers for half-bridge measurement.
The CNR4 design is light weight and has an integrated solar shield that reduces thermal effects
on both the short-wave and the long-wave measurements. The cables are made from
Santoprene® jacket, which is intended for outdoor use, and is resistant to a variety of pollutants
and UV-radiation. The mounting rod can be unscrewed for transport.
An optional ventilation unit with a heater, CNF4, is designed as an extension of the solar shield
and can be fitted to the CNR4 or retrofitted later. The heater/ventilation unit is compact and
provides efficient air-flow over the domes and windows to minimize the formation of dew and to
reduce the frequency of cleaning. The integrated heater can be used to melt frost.
The CNR4 design is such that both the upward facing and the downward-facing instruments
measure the energy that is received from the whole hemisphere (180° field of view). The output is
expressed in W/m2. The total spectral range that is measured is roughly from 0.3 to 42μm. This
spectral range covers both the short-wave solar radiation, 0.3 to 2.8μm, and the long-wave far
infrared radiation, 4.5 to 42μm. The gap between these two produces negligible errors.
The CNR4 is manufactured by Kipp & Zonen, but cabled for use with Campbell Scientific data
loggers.
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Features:
lResearch-grade performance
lMeniscus dome on upper long-wave detector allows water droplets to easily roll off of it
and increases field of view to nearly 180°
lInternal temperature sensors provide temperature compensation of measurements
lDrying cartridge helps keep the electronics dry
lCompatible with the CNF4 ventilation unit with heater that reduces formation of dew and
melts frost
lSeparate outputs of short-wave and long-wave infrared radiation for better accuracy and
more thorough quality assurance
lSolar shield reduces thermal effects on the sensors
lCompatible with Campbell Scientific CRBasic data loggers: CR6 series, CR3000, CR1000X,
and CR1000
6. Specifications
The properties of the CNR4 are mainly determined by the properties of the individual probes.
Generally, the accuracy of the CNR4 will be higher than that of competitive net-radiometers,
because the solar radiation measurement performed by the pyranometer is accurate, and offers
a traceable calibration. Also the optionally integrated heater/ventilator unit improves the
accuracy. Due to the fact that the net short-wave radiation can be very intense, 1000 W/m2
compared to a typical –100 W/m2 net long-wave radiation, the accuracy of the short-wave
radiation measurement is critical. Wind corrections, as applied by less accurate competitive
instruments are not necessary. The robust materials used imply that the CNR4 will not suffer
damages inflicted by birds. FIGURE 6-1 (p. 7) and FIGURE 6-2 (p. 7) show the CNR4 with and
without the CNF4 heater/ventilator. From a spectral point of view, the pyranometer and
pyrgeometer are complementary, and together they cover the full spectral range.
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FIGURE 6-1. The CNR4 net radiometer with cables and mounting rod, top view
FIGURE 6-2. The CNR4 net radiometer with CNF4 heater/ventilator unit, top view
6.1 CNR4 specifications
Sensor sensitivities: Four probes with unique sensitivity values. Please refer to
the calibration sheets or label on the bottom of the sensor
for the sensitivity values.
Operating temperature: –40 to 80 °C (–40 to 176 °F)
Operating humidity: 0 to 100% RH
Bubble level sensitivity: < 0.5°
Sensor type: Thermopile
Receiver paint: Carbon Black
Desiccant: Silica gel (replaceable)
Housing material: Anodized aluminum body
Shock/vibration: IEC 721-3-2-2m2
CE: Complies with EC guideline 89/336/EEC 73/23/EEC
Environmental protection: IP 67
Requirements for data acquisition 
Radiation components: 4 differential or 4 single-ended analog terminals
Thermistor: 1 voltage excitation and 1 single-ended analog terminal
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Pt-100 temperature: 1 current excitation and 1 differential analog terminal
Cable length: User defined
Weight 
Sensor: 0.85 kg (1.89 lb) without cables
Heater/ventilator, CNF4
(optional): 0.50 kg (1.11 lb) without cables
Mounting rod: 34.7 cm (13.67 in) length
1.6 cm (0.63 in) diameter
6.2 Pyranometer specifications
Spectral range: 305 to 2800 nm (50% points)
Sensitivity: 10 to 20 µV/W/m2
Response time1:< 18 seconds (95% response)
Non-linearity1:< 1% (0 to 1000 W m–2 irradiance)
Non-stability1:< 1%
Temperature dependence of
sensitivity1:< 4% (–10 to 40 °C)
Tilt response1:< 1% at any angle with 1000 W/m2
Directional error1:< 20 W/m2 at angle up to 80° with 1000 W/m2
Zero offset due to 0 to -200 W/m2
IR net irradiance1:< 15 W/m2
Zero offset due to temperature
change1:< 3 W/m2 (5 K/hr temperature change)
< 1 W/m2 (with CNF4 installed)
Operating temperature: –40 to 80 °C
Field of view 
Upper detector: 180°
Lower detector: 150° (due to lower solar shield to prevent illumination at low
zenith angles)
Maximum solar irradiance: 2000 W/m2
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Expected accuracy for daily totals: ±10 %
Typical signal output for
atmospheric application: 0 to 15 mV
Impedance: 20 to 200 Ω, typically 50 Ω
Detector: Copper-constantan multi-junction thermopile
Level accuracy: 1 degree
Irradiance: 0 to 2000 W/m2
Spectral selectivity: < 3% (330 to 1500 nm spectral interval)
Uncertainty in daily total: < 5% (95% confidence level)
Instrument calibration: Indoors. Side by side against reference CMP3 pyranometer
according to ISO 9847:1992 annex A.3.1
1Indicates ISO specifications.
6.3 Pyrgeometer specifications
Spectral range: 4.5 to 42 μm (50% points)
Sensitivity: 5 to 15 μV/W/m2
Impedance: 20 to 200 Ω (typically 50 Ω)
Response time: < 18 seconds (95% response)
Non-linearity: < 1% (–250 to +250 W/m2 irradiance)
Temperature dependence of
sensitivity: < 4% (–10 to 40 °C)
Tilt error: < 1% (deviation when tilted at any angle off horizontal)
Zero offset due to temperature
change: ±4 W/m2 (5 K/hr temperature change)
Field of view 
Upper: 180 degrees
Lower: 150 degrees
Net-irradiance: –250 to +250 W/m2
Non-stability: < 1% (sensitivity change per year)
Window heating offset: < 6 W/m2 (1000 W/m2 solar irradiance)
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Uncertainty in daily total: < 10% (95% confidence level) indoor calibration
Typical signal output for
atmospheric application: ±5 mV
Temperature sensors 
Thermistor: 10 kΩ
Pt-100: DIN class A
Instrument calibration: Indoors, side by side against reference CG(R) 3
pyrgeometer. On request outdoors, side by side against
reference CG(R) 4 pyrgeometer
6.4 Optional CNF4 heater/ventilator
The purpose of the heater/ventilator is to prevent dew deposition on the pyrgeometer and
pyrgeometer window, thus enhancing the measurement accuracy and reliability. Using the
heater/ventilator will have negligible effect on the pyranometer reading.
Generally, the errors caused by the heater/ventilator will be small relative to the errors that would
have been caused by water deposition.
6.4.1 CNF4 specifications
Heater 
Power consumption: 10 W @ 12 VDC (15 Ω)
Ventilator 
Power consumption: 5 W @ 12 VDC
Supply voltage: 8 to 13.5 VDC
Weight without cable: 0.5 kg (1.11 lb)
Operating temperature: –40 to 80 °C
7. Installation
If you are programming your data logger with Short Cut, skip Wiring (p. 13) and Data logger
programming (p. 17). Short Cut does this work for you. See QuickStart (p. 2) for a tutorial.
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7.1 Siting considerations
1. Mount the sensor so no shadows or reflections will be cast on it at any time of day from
obstructions such as trees, buildings, or the mast or structure on which it is mounted. 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 10h. Shadows or surface disturbances with a radius
<0.1h will affect the measurement by less than 1%.
2. To avoid shading or reflection effects and to promote spatial averaging, the CNR4 should
be mounted at least 1.5m above the ground or crop surface. It is recommended that the
CNR4 be mounted to a separate vertical pipe at least 25ft from any other mounting
structures.
3. The sensor should be mounted with the cable pointing towards the nearest magnetic pole.
For example, in the Northern Hemisphere, point the cable toward the North Pole.
7.2 Mounting
A mounting bracket kit is used to mount the CNR4 directly to a vertical pipe, or to a crossarm.
Mount the sensor as follows:
1. Attach the mounting rod to the CNR4 (see FIGURE 7-1 (p. 11)).
FIGURE 7-1. Attaching the mounting rod to the CNR4 body
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2. Attach the 26120 mounting bracket to the vertical mounting pipe, or CM200-series
crossarm using the provided U-bolt (see FIGURE 7-2 (p. 12)). If mounted to a vertical pipe,
ensure that the pipe does not cast a reflection on the sensor. This includes both the
incoming and outgoing sections of the sensor.
FIGURE 7-2. Attaching the CNR4 onto the mounting rod using vertical pole or
horizontal crossarm
CNR4 Net Radiometer12

3. Insert the sensor support arm into the mounting block of the mounting bracket kit. Make
sure the sensor points in the direction of the arrows that appear after the word SENSOR on
top of the bracket (see FIGURE 7-2 (p. 12)).
NOTE:
If the CNR4 is being used at a location where snow and ice accumulate, or high winds
are expected, then the mounting rod should not be fully extended.
CAUTION:
Do not attempt to rotate the instrument using the sensor heads, or you may damage
the sensors; use the mounting rod only.
4. Perform a coarse leveling of the sensor using the sensor bubble level.
5. Tighten the four screws on top of the mounting bracket to properly secure the support arm
so that it does not rotate (see FIGURE 7-2 (p. 12)).
CAUTION:
The four screws need to be tightened evenly to ensure that the screwhead is in full
contact with the V-plate.
6. Perform the fine leveling using the two spring-loaded leveling screws—one on the front
and the other on the back of the bracket.
7. Route the sensor cable to the instrument enclosure.
8. Use the UV-resistant cable ties included with the tripod or tower to secure the cable to the
vertical pipe or crossarm and tripod/tower.
7.3 Wiring
NOTE:
This manual provides wiring information for CNR4 sensors and cables purchased from
Campbell Scientific. Sensors and cables purchased directly from Kipp and Zonen will have
different wiring.
The CNR4 has two outputs for short-wave radiation, two outputs for long-wave radiation,
thermistor output, and Pt-100 temperature sensor output. The optional CNF4 heater/ventilator
unit has power wires for heater and ventilator and a control/pulse wire for the tachometer.
The CNR4 has a SOLAR cable and a TEMP cable (FIGURE 7-3 (p. 14)). Connect the SOLAR cable to
the S port and the TEMP cable to the T port (FIGURE 7-4 (p. 14)). The two cables, SOLAR and
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TEMP, have identical connectors, and therefore ensure that the correct cables are connected to
the correct ports of the sensor.
FIGURE 7-3. The CNR4 sensor with SOLAR and TEMP cables
FIGURE 7-4. The marks on the end of the CNR4: S for SOLAR cable, and T for TEMP cable
The four radiation outputs can be measured using differential or single-ended inputs on the data
logger. A differential voltage measurement is recommended because it has better noise rejection
than a single-ended measurement. If differential terminals are not available, single-ended
measurements can be used. The acceptability of a single-ended measurement can be
determined by comparing the results of single-ended and differential measurements made
under the same conditions.
NOTE:
When differential inputs are used, jumper the low side of the input to ⏚ to keep the signal in
common mode range.
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Table 7-1 (p. 15) shows the data logger connections for the SOLAR cable, and Table 7-2 (p. 16)
shows the data logger connections for the TEMP cable. The cables have the white band at the
pigtail end of the cable with the color keys (FIGURE 7-5 (p. 15), FIGURE 7-6 (p. 17)).
FIGURE 7-5. Labels on the pigtail end of the SOLAR cable
Table 7-1: SOLAR cable (wire color, function, and data logger connection)
Wire
color Wire function Differential data logger connection terminal
Single-ended data logger
connection terminal
Red Pyranometer
top signal
U configured for differential high
analog input1, DIFF H (differential
high, analog-voltage input)
U configured for single-ended
analog input1, SE (single-ended,
analog-voltage input)
Blue Pyranometer
top reference
U configured for differential low
analog input1, 2, DIFF L (differential
low, analog-voltage input)2
⏚ (analog ground)
White Pyranometer
bottom signal
U configured for differential high
analog input1, DIFF H (differential
high, analog-voltage input)
U configured for single-ended
analog input1, SE (single-ended,
analog-voltage input)
Black
Pyranometer
bottom
reference
U configured for differential low
analog input1, 2, DIFF L (differential
low, analog-voltage input)2
⏚ (analog ground)
Grey Pyrgeometer
top signal
U configured for differential high
analog input1, DIFF H (differential
high, analog-voltage input)
U configured for single-ended
analog input1, SE (single-ended,
analog-voltage input)
Yellow Pyrgeometer
top reference
U configured for differential low
analog input1, 2, DIFF L (differential
low, analog-voltage input)2
⏚ (analog ground)
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Table 7-1: SOLAR cable (wire color, function, and data logger connection)
Wire
color Wire function Differential data logger connection terminal
Single-ended data logger
connection terminal
Brown Pyrgeometer
bottom signal
U configured for differential high
analog input1, DIFF H (differential
high, analog-voltage input)
U configured for single-ended
analog input1, SE (single-ended,
analog-voltage input)
Green
Pyrgeometer
bottom
reference
U configured for differential low
analog input1, 2, DIFF L (differential
low, analog-voltage input)2
⏚ (analog ground)
Clear Shield ⏚ (analog ground) ⏚ (analog ground)
1U terminals are automatically configured by the measurement instruction.
2Jumper to ⏚ with a user-supplied wire.

Table 7-2: TEMP cable (wire color, function, and data logger connection)
Wire color Wire
function
Data logger connection terminal
Using thermistor1Using Pt-1001
White Thermistor
signal
U configured for single-ended
analog input2, SE (single-
ended, analog-voltage input)
N/A
Red
Thermistor
voltage
excitation
U configured for voltage
excitation2, EX, VX (voltage
excitation)
N/A
Black Thermistor
reference ⏚ (analog ground) N/A
Green PRT (Pt-100)
signal N/A
U configured for differential high
analog input2, DIFF H (differential
high, analog-voltage input)
Yellow
PRT (Pt-100)
signal
reference
N/A
U configured for differential low
analog input2, DIFF L (differential
low, analog-voltage input)
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Table 7-2: TEMP cable (wire color, function, and data logger connection)
Wire color Wire
function
Data logger connection terminal
Using thermistor1Using Pt-1001
Grey
PRT (Pt-100)
current
excitation
N/A U configured for current
excitation2, IX (current excitation)
Brown
PRT (Pt-100)
current
return
N/A IXR (current excitation return),
⏚ (CR6 only)
Clear Shield ⏚ (analog ground) ⏚ (analog ground)
1Pull back unused wires and tie them around the TEMP cable using a cable tie or electrical tape to avoid possible
damage to the thermistor or Pt-100, due to electrical short circuit.
2U terminals are automatically configured by the measurement instruction.
FIGURE 7-6. Labels on the pigtail end of the TEMP cable
7.4 Data logger programming
Short Cut is the best source for up-to-date programming code for Campbell Scientific data
loggers. If your data acquisition requirements are simple, you can probably create and maintain a
data logger program exclusively with Short Cut. If your data acquisition needs are more complex,
the files that Short Cut creates are a great source for programming code to start a new program
or add to an existing custom program.
NOTE:
Short Cut cannot edit programs after they are imported and edited in CRBasic Editor.
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