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 [phone]. 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.
CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____
815 West 1800 North
Logan, Utah 84321-1784

For all returns, the customer must fill out a “Declaration of Hazardous Material
and Decontamination” form and comply with the requirements specified in it.
The form is available from our website at
completed form must be either emailed to [e-mail]
435-750-9579. Campbell Scientific will not process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer’s expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

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.

8

CNR1 Net Radiometer

DATALOGGER

EX1

4WPB100

10K

5H

100

5L

6H

FIGURE 5-1. CNR1 Schematic

H

CNR1

L
G

Red

Yellow

PT-100

6L

Green
Blue

FIGURE 5-2. Interfacing the Pt-100 Using the 4WPB100 Module

9

CNR1 Net Radiometer

TABLE 5-1. Datalogger Connections for Differential Measurement, When Using a 4WPB100

The four radiation outputs can be measured using Differential or Single-Ended
inputs on the datalogger. A differential voltage measurement (Instruction 2) is
recommended because it has better noise rejection than a single-ended
measurement. When differential inputs are used, jumper the low side of the
input to AG or

to keep the signal in common mode range.

Function

Color

CR10X

CR800, CR850,

CR1000

21X/CR7, CR23X

CM3 Up Signal Red Differential Input (H) Differential Input (H) Differential Input (H)

CM3 Up Reference *Blue Differential Input (L) Differential Input (L) Differential Input (L)

CM3 Down Signal White Differential Input (H) Differential Input (H) Differential Input (H)

CM3 Down Reference *Black Differential Input (L) Differential Input (L) Differential Input (L)

CG3 Up Signal Grey or

Differential Input (H) Differential Input (H) Differential Input (H)

†Orange

CG3 Up Reference *Yellow Differential Input (L) Differential Input (L) Differential Input (L)

CG3 Down Signal Brown Differential Input (H) Differential Input (H) Differential Input (H)

CG3 Down Reference *Green Differential Input (L) Differential Input (L) Differential Input (L)

Shield Shield G

*Jumper to AG or with user supplied wire.
†Cables extended > 48’ have an orange wire.

Pt-100 Temperature Sensor Connections to 4WPB100 a nd Da talogger

Function Color 4WPB100 Datalogger

Black Wire Excitation
H Differential Input (H)

Pt-100 Excitation + Red L Differential Input (L)

Pt-100 Excitation - Blue G (AG CR10X/CR510)

Pt-100 Signal + Yellow Differential Input (H)
Pt-100 Signal – Green Differential Input (L)

TABLE 5-2. Datalogger Connections for Single-Ended Measurement, When Using a 4WPB100

Function

Color

CR10X

CR23X, 21X, CR7

CR800, CR850,

CR1000

CM3 Up Signal Red Single-Ended Input Single-Ended Input Single-Ended Input

CM3 Up Reference Blue AG

CM3 Down Signal White Single-Ended Input Single-Ended Input Single-Ended Input

CM3 Down Reference Black AG

CG3 Up Signal Grey or Ora ng e Single-Ended Input Single-Ended Input Single-Ended Input

CG3 Up Reference Yellow AG

CG3 Down Signal Brown Single-Ended Input Single-Ended Input Single-Ended Input

CG3 Down Reference Green AG

Shield Shield G

10

CNR1 Net Radiometer

TABLE 5-3. CR3000 and CR5000 Connections

for Differential Measurement

Function Color CR3000/CR5000

CM3 Up Signal Red Differential Input (H)

CM3 Up Reference Blue Differential Input (L)

CM3 Down Signal White Differential Input (H)

CM3 Down Reference Black Differential Input (L)

CG3 Up Signal Grey or Orange Differential Input (H)

CG3 Up Reference Yellow Differential Input (L)

CG3 Down Signal Brown Differential Input (H)

CG3 Down Reference Green Differential Input (L)

PT-100 Signal + Yellow Diffe rential Input (H)

PT-100 Signal - Green Differential Input (L)

PT-100 Current Excitation + Red Current Excitation IX

PT-100 Current Excitation - Blue Current Excitation IXR

Shield Clear

6. Datalogger Programming

The CNR1 outputs four voltages that typically range from 0 to 15 mV for the
CM3 sensors, and ± 5 mV for the CG3 sensors. A differential voltage
measurement (VoltDiff or Instruction 2) is recommended because it has better
noise rejection than a single-ended measurement. If differential channels are
not available, single-ended measurements (VoltSe or Instruction 1) can be
used. The acceptability of a single-ended measurement can be determined by
simply comparing the results of single-ended and differential measurements
made under the same conditions.

For the CR3000 and CR5000, one differential channel and a current excitation
channel are required to measure the PT-100.

For the other dataloggers, two differential channels and the 4WPB100 module
are required to measure the Pt-100 temperature sensor.

NOTE

The 4WPB100 is included with the CNR1 sensor purchased from
CSI.

11

CNR1 Net Radiometer

6.1 Calibration Factor

FIGURE 6-1. 4WPB100 Module

Each CNR1 is provided with a ‘Certificate of Calibration’ by the manufacturer
that shows the sensor serial number and ‘sensitivity’, or calibration factor. The
serial number and sensitivity are also shown on a label attached to the sensor.

-2

The calibration factor is in units of μV/(W m
units of (W m
To convert the units, divide the calibration factor into 1000. For example, if
the calibration factor is 7.30 μV/(W m

-2

(W m

)/mV.

-2

)/mV for the multiplier parameter in the datalogger program.

-2

), which needs to be converted to

), the multiplier is 1000/7.3 = 136.99

6.2 Example Programs

6.2.1 Example 1, CR1000 Using Differential Channels

Program Example 1 requires six differential channels and the 4WPB100
module to measure the four radiation outputs and the Pt-100 temperature
sensor. The program measures the sensors every 2 seconds and calculates and
stores the following data to final storage every 60 minutes:

Year
Julian Day
Hour/Minute
Avg CM3 Up (shortwave radiation)
Avg CM3 Down (shortwave radiation)
Avg CG3 Up (longwave radiation)
Avg CG3 Down (longwave radiation)
Avg CNR1 temperature (degrees C)
Avg CNR1 temperature (degrees K)
Avg Net shortwave radiation
Avg Net longwave radiation
Avg Albedo
Avg Total Net radiation
Avg temperature corrected CG3 Up
Avg temperature corrected CG3 Down

12

'CR1000
'Declare Variables and Units

Public Batt_Volt
Public CM3Up
Public CM3Dn
Public CG3Up
Public CG3Dn
Public CNR1TC
Public CNR1TK
Public NetRs
Public NetRl
Public Albedo
Public UpTot
Public DnTot
Public NetTot
Public CG3UpCo
Public CG3DnCo

Units Batt_Volt=Volts
Units CM3Up=W/meter²
Units CM3Dn=W/meter²
Units CG3Up=W/meter²
Units CG3Dn=W/meter²
Units CNR1TC=Deg C
Units CNR1TK=K
Units NetRs=W/meter²
Units NetRl=W/meter²
Units Albedo=W/meter²
Units UpTot=W/meter²
Units DnTot=W/meter²
Units NetTot=W/meter²
Units CG3UpCo=W/meter²
Units CG3DnCo=W/meter²

'Define Data Tables

DataTable(Table1,True,-1)
DataInterval(0,60,Min,10)
Average(1,CM3Up,FP2,False)
Average(1,CM3Dn,FP2,False)
Average(1,CG3Up,FP2,False)
Average(1,CG3Dn,FP2,False)
Average(1,CNR1TC,FP2,False)
Average(1,CNR1TK,FP2,False)
Average(1,NetRs,FP2,False)
Average(1,NetRl,FP2,False)
Average(1,Albedo,FP2,False)
Average(1,UpTot,FP2,False)
Average(1,DnTot,FP2,False)
Average(1,NetTot,FP2,False)
Average(1,CG3UpCo,FP2,False)
Average(1,CG3DnCo,FP2,False)
EndTable

CNR1 Net Radiometer

13

CNR1 Net Radiometer

'Main Program

BeginProg
Scan(2,Sec,1,0)

'Default Datalogger Battery Voltage measurement Batt_Volt:

Battery(Batt_Volt)

'CNR1 Net Radiomet er me asureme nts CM 3Up, CM3Dn, CG3U p, CG 3Dn, CN R1TC, CN R1TK ,
'NetRs, NetRl, Albedo, UpTot, DnTot, NetTot, CG3UpCo, and CG3DnCo:

* VoltDiff(CM3Up,1,mV25,1,True,0,_60Hz,100.0,0)
* VoltDiff(CM3Dn,1,mV25,2,True,0,_60Hz,100.0,0)
* VoltDiff(CG3Up,1,mV7_5,3,True,0,_60Hz,100.0,0)
* VoltDiff(CG3Dn,1,mV7_5,4,True,0,_60Hz,100.0,0)
** BrHalf4W (CNR1TC,1,mV25,mV25,5,Vx1,1,2100,True ,True ,0,250,1.0,0)
PRT(CNR1TC,1,CNR1TC,1,0)
CNR1TK=CNR1TC+273.15
NetRs=CM3Up-CM3Dn
NetRl=CG3Up-CG3Dn
Albedo=CM3Dn/CM3Up
UpTot=CM3Up+CG3Up
DnTot=CM3Dn+CG3Dn
NetTot=UpTot-DnTot
CG3UpCo=CG3Up+5.67*10^-8*CNR1TK^4
CG3DnCo=CG3Dn+5.67*10^-8*CNR1TK^4

'Call Data Tables and Store Data

CallTable(Table1)
NextScan
EndProg

* mV20 range for the CR5000
** mV50 range (both) with 4200 mV excitation for CR5000

6.2.2 Example 2, CR5000 Using Differential Channels (no 4WPB100)

Program Example 2 requires five differential channels and one current
excitation channel to measure the four radiation outputs and the Pt-100
temperature sensor. The program measures the sensors every second and
calculates and stores the following data to final storage every 60 minutes:

Year
Julian Day
Hour/Minute
Avg CM3 Up (shortwave radiation)
Avg CM3 Down (shortwave radiation)
Avg CG3 Up (longwave radiation)
Avg CG3 Down (longwave radiation)
Avg CNR1 temperature (degrees C)
Avg CNR1 temperature (degrees K)
Avg Net shortwave radiation
Avg Net longwave radiation
Avg Albedo
Avg Total Net radiation
Avg temperature corrected CG3 Up
Avg temperature corrected CG3 Down

14

CNR1 Net Radiometer

'CR5000 Series Datalogger
'ANALOG INPUT

'1H CM3 UP - downwelling shortwave radiation signal (red)
'1L CM3 UP - downwelling shortwave radiation signal reference (blue)
'gnd CNR1 shield (clear)

'2H CM3 DOWN - upwelling shortwave radiation signal (white)
'2L CM3 DOWN - upwelling shortwave radiation signal reference (black)

'3H CG3 UP - downwelling longwave radiation signal (gray)
'3L CG3 UP - downwelling longwave radiation signal reference (yellow)

'4H CG3 DOWN - upwelling longwave radiation signal (brown)
'4L CG3 DOWN - upwelling longwave radiation signal reference (green)

'6H CNR1 Pt100 (yellow)
'6L CNR1 Pt100 (green)

'Current Excitation
'IX1 CNR1 Pt100 (red)
'IXR CNR1 Pt100 (blue)

'Declare Variables and Units

Public Batt_Volt
Public CM3Up
Public CM3Dn
Public CG3Up
Public CG3Dn
Public CNR1TC
Public CNR1TK
Public NetRs
Public NetRl
Public Albedo
Public UpTot
Public DnTot
Public NetTot
Public CG3UpCo
Public CG3DnCo

Units Batt_Volt=Volts
Units CM3Up=W/meter²
Units CM3Dn=W/meter²
Units CG3Up=W/meter²
Units CG3Dn=W/meter²
Units CNR1TC=Deg C
Units CNR1TK=K
Units NetRs=W/meter²
Units NetRl=W/meter²
Units Albedo=W/meter²
Units UpTot=W/meter²
Units DnTot=W/meter²
Units NetTot=W/meter²
Units CG3UpCo=W/meter²
Units CG3DnCo=W/meter²

15

CNR1 Net Radiometer

'Define Data Tables

DataTable(Table1,True,-1)
DataInterval(0,60,Min,10)
Average(1,CM3Up,FP2,False)
Average(1,CM3Dn,FP2,False)
Average(1,CG3Up,FP2,False)
Average(1,CG3Dn,FP2,False)
Average(1,CNR1TC,FP2,False)
Average(1,CNR1TK,FP2,False)
Average(1,NetRs,FP2,False)
Average(1,NetRl,FP2,False)
Average(1,Albedo,FP2,False)
Average(1,UpTot,FP2,False)
Average(1,DnTot,FP2,False)
Average(1,NetTot,FP2,False)
Average(1,CG3UpCo,FP2,False)
Average(1,CG3DnCo,FP2,False)
EndTable

'Main Program

BeginProg
Scan(1,Sec,1,0)

'Default Datalogger Battery Voltage measurement Batt_Volt:

Battery(Batt_Volt)

'CNR1 Net Radiometer measurements CM3Up, CM3Dn, CG3Up, CG3Dn, CNR1TC, CNR1TK,
'NetRs, NetRl, Albedo, UpTot, DnTot, NetTot, CG3UpCo, and CG3DnCo:
'CNR1 Sensitivity 7.30 uV/m^2

VoltDiff(CM3Up,1,mV20C,1,True,200,250,136.99,0)
VoltDiff(CM3Dn,1,mV20C,2,True,200,250,136.9,0)
VoltDiff(CG3Up,1,mV20C,3,True,200,250,136.9,0)
VoltDiff(CG3Dn,1,mV20,4,True,200,250,136.9,0)
Resistance (CNR1TC,1,mV200,6,Ix1,1,1675,True ,True,200,250,1.0,0)

'Formulate the ratio Rs/R0

CNR1TC=CNR1TC/100
PRT(CNR1TC,1,CNR1TC,1,0)

'Compute Net short-wave radiation, Net long-wave radiation, Albedo and Net Radiation

CNR1TK=CNR1TC+273.15
NetRs=CM3Up-CM3Dn
NetRl=CG3Up-CG3Dn
Albedo=CM3Dn/CM3Up
UpTot=CM3Up+CG3Up
DnTot=CM3Dn+CG3Dn
NetTot=UpTot-DnTot
CG3UpCo=CG3Up+5.67*10^-8*CNR1TK^4
CG3DnCo=CG3Dn+5.67*10^-8*CNR1TK^4

'Call Data Tables and Store Data

CallTable(Table1)
NextScan
EndProg

16

CNR1 Net Radiometer

6.2.3 Example 3, CR23X Program Using Differential Channels

Program Example 3 requires six differential channels and the 4WPB100
module to measure the four radiation outputs and the Pt-100 temperature
sensor. The program measures the sensors every 2 seconds and calculates and
stores the following data to final storage every 60 minutes:

Array ID
Year
Julian Day
Hour/Minute
Avg CM3 Up (shortwave radiation)
Avg CM3 Down (shortwave radiation)
Avg CG3 Up (longwave radiation)
Avg CG3 Down (longwave radiation)
Avg CNR1 temperature (degrees C)
Avg CNR1 temperature (degrees K)
Avg Net shortwave radiation
Avg Net longwave radiation
Avg Albedo
Avg Total Net radiation
Avg temperature corrected CG3 Up
Avg temperature corrected CG3 Down

Wiring for Program Example 3

Color

Red CM3 Up Signal 1H

Blue CM3 Up Reference 1L
White CM3 Down Signal 2H
Black CM3 Down Reference 2L

Grey or Orange CG3 Up Signal 3H

Yellow CG3 Up Reference 3L

Brown CG3 Down Signal 4H

Green CG3 Down Reference 4L
Shield Shield

Pt-100 Temperature Sensor Connections to 4WPB100 a nd Da talogger

Color Function 4WPB100 CR23X

Black Wire EX1

H 5H

Red Pt-100 Excitation + L 5L

Blue Pt-100 Excitation - G

Yellow Pt-100 Signal + 6H

Green Pt-100 Signal - 6L

Function

Example CR23X

Program

Channels Used

17

CNR1 Net Radiometer

;{CR23X}
;Program Example 1 for CR23X datalogger
;
;CNR1 sensitivity for program example = 7.30 uV/W/m^2
;Multiplier for measurement instructions = 1000/7.30 = 136.99
;
;*Table 1 Program

01: 2 Execution Interval (seconds)

;Measure CM3 Up and CM3 Down (shortwave radiation)
;Note: Multiplier (Parameter 5) will be different for each CNR1

1: Volt (Diff) (P2)
1: 2 Reps
2: 22+ 50 mV, 60 Hz Reject, Slow Range
3: 1* DIFF Channel
4: 1* Loc [ CM3_up ]
5: 136.99 Mult ; mult = 1000/CNR1 sensitivity
6: 0 Offset

;Measure CG3 Up and CG3 Down (longwave radiation)
;Note: Multiplier (Parameter 5) will be different for each CNR1

2: Volt (Diff) (P2)
1: 2 Reps
2: 21++ 10 mV, 60 Hz Reject, Slow Range
3: 3* DIFF Channel
4: 3* Loc [ CG3_up ]
5: 136.99 Mult ; mult = 1000/CNR1 sensitivity
6: 0 Offset

;Measure CNR1 temperature

3: Full Bridge w/mv Excit (P9)
1: 1 Reps
2: 22** 50 mV, 60 Hz Reject, Slow, Ex Range
3: 22** 50 mV, 60 Hz Reject, Slow, Br Range
4: 5* DIFF Channel
5: 1 Excite all reps w/Exchan 1
6: 4200*** mV Excitation
7: 5* Loc [ Temp_C ]
8: 1 Mult
9: 0 Offset

4: Temperature RTD (P16)
1: 1 Reps
2: 5 R/R0 Loc [ Temp_C ]
3: 5 Loc [ Temp_C ]
4: 1.0 Mult
5: 0 Offset

5: Z=X+F (P34)
1: 5 X Loc [ Temp_C ]
2: 273.15 F
3: 6 Z Loc [ Temp_K ]

18

;Net CM3 shortwave radiation = CM3 Up - CM3 Down

6: Z=X-Y (P35)
1: 1 X Loc [ CM3_up ]
2: 2 Y Loc [ CM3_dn ]
3: 7 Z Loc [ Net_Rs ]

;Net CG3 longwave radiation = CG3 Up - CG3 Down

7: Z=X-Y (P35)
1: 3 X Loc [ CG3_up ]
2: 4 Y Loc [ CG3_dn ]
3: 8 Z Loc [ Net_Rl ]

;Albedo = CM3 Down / CM3 Up

8: Z=X/Y (P38)
1: 2 X Loc [ CM3_dn ]
2: 1 Y Loc [ CM3_up ]
3: 9 Z Loc [ Albedo ]

;Net total radiation = (CM3 Up + CG3 Up) - (CM3 Down + CG3 Down)

9: Z=X+Y (P33)
1: 1 X Loc [ CM3_up ]
2: 3 Y Loc [ CG3_up ]
3: 23 Z Loc [ Up_total ]

10: Z=X+Y (P33)
1: 2 X Loc [ CM3_dn ]
2: 4 Y Loc [ CG3_dn ]
3: 24 Z Loc [ Dn_total ]

11: Z=X-Y (P35)
1: 23 X Loc [ Up_total ]
2: 24 Y Loc [ Dn_total ]
3: 10 Z Loc [ Net_total ]

;Correct CG3 Up and CG3 Down for temperature

; CG3_upCor = CG3_up+5.67 ⋅ 10-8 ∗ Temp_K4
; CG3_dnCor = CG3_dn+5.67 ⋅ 10-8 ∗ Temp_K4

12: Z=F (P30)
1: 5.67 F
2: -8 Exponent of 10
3: 25 Z Loc [ scratch_1 ]

13: Z=F (P30)
1: 4 F
2: 0 Exponent of 10
3: 26 Z Loc [ scratch_2 ]

14: Z=X^Y (P47)
1: 6 X Loc [ Temp_K ]
2: 26 Y Loc [ scratch_2 ]
3: 27 Z Loc [ scratch_3 ]

CNR1 Net Radiometer

19

CNR1 Net Radiometer

15: Z=X*Y (P36)
1: 25 X Loc [ scratch_1 ]
2: 27 Y Loc [ scratch_3 ]
3: 28 Z Loc [ scratch_4 ]

16: Z=X+Y (P33)
1: 3 X Loc [ CG3_up ]
2: 28 Y Loc [ scratch_4 ]
3: 11 Z Loc [ CG3_upCor ]

17: Z=X+Y (P33)
1: 4 X Loc [ CG3_dn ]
2: 28 Y Loc [ scratch_4 ]
3: 12 Z Loc [ CG3_dnCor ]
;

;Output data to final storage every 60 minutes

18: If time is (P92)
1: 0 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 10 Set Output Flag High (Flag 0)

19: Real Time (P77)
1: 0220 Day,Hour/Minute (midnight = 2400)

20: Average (P71)
1: 12 Reps
2: 1 Loc [ CM3_dn ]

* Proper entries will vary with program and input channel usage.
** 25 mV range for CR10X, 50 mV for 21X and CR7
*** 4200 mV for 21X and CR7, 2100 mV for CR10X
+ 25 mV range for CR10X, 50 mV for 21X and CR7
++ 7.5 mV range for CR10X, 5 mV for 21X and CR7

20

6.2.4 Example 4, CR23X Program Using Single-Ended Channels

Program Example 4 requires four single-ended channels to measure the four
radiation outputs, and two differential channels and the 4WPB100 module to
measure the Pt-100 temperature sensor. The program measures the sensors
every 2 seconds and stores the following data to final storage every 60 minutes:

Array ID
Year
Day
Hour/Minute
Avg CM3 down (shortwave radiation)
Avg CM3 up (shortwave radiation)
Avg CG3 down (longwave radiation)
Avg CG3 up (longwave radiation)
Avg CNR1 temperature (degrees C)
Avg CNR1 temperature (degrees K)

CNR1 Net Radiometer

Wiring for Program Example 4

Color Function Example CR23X Program

Channels Used

Red CM3 Up Signal SE1

Blue CM3 Up Reference

White CM3 Down Signal SE2

Black CM3 Down Reference

Grey or Orange CG3 Up Signal SE3

Yellow CG3 Up Reference

Brown CG3 Down Signal SE4

Green CG3 Down Reference
Shield Shield

Pt-100 Temperature Sensor Connections to 4WPB100 a nd Da talogger

Color Function 4WPB100 CR23X

H 5H

Red Pt-100 Excitation + L 5L

Blue Pt-100 Excitation - G

Yellow Pt-100 Signal + 6H

Green Pt-100 Signal - 6L

;{CR23X}
;
;CNR1 sensitivity for program example = 7.30 uV/W/m^2
;Multiplier for measurement instructions = 1000/7.3 = 136.99

*Table 1 Program
01: 2 Execution Interval (seconds)

;Measure CM3 Up and CM3 Down (shortwave radiation)
;Note: Multiplier (Parameter 6) will be different for each CNR1

1: Volt (SE) (P1)
1: 2 Reps
2: 22 50 mV, 60 Hz Reject, Slow Range
3: 1 SE Channel
4: 1 Loc [ CM3_up ]
5: 136.99 Mult ; mult = 1000/CNR1 sensitivity
6: 0 Offset

;Measure CG3 Up and CG3 Down (longwave radiation)
;Note: Multiplier (Parameter 6) will be different for each CNR1

2: Volt (SE) (P1)
1: 2 Reps
2: 21 10 mV, 60 Hz Reject, Slow Range
3: 3 SE Channel
4: 3 Loc [ CG3_up ]
5: 136.99 Mult ; mult = 1000/CNR1 sensitivity
6: 0 Offset

21

CNR1 Net Radiometer

;Measure CNR1 temperature

3: Full Bridge w/mv Excit (P9)
1: 1 Reps
2: 22 50 mV, 60 Hz Reject, Slow, Ex Range
3: 22 50 mV, 60 Hz Reject, Slow, Br Range
4: 5 DIFF Channel
5: 1 Excite all reps w/Exchan 1
6: 4200 mV Excitation
7: 5 Loc [ Temp_C ]
8: 1 Mult
9: 0 Offset

4: Temperature RTD (P16)
1: 1 Reps
2: 5 R/R0 Loc [ Temp_C ]
3: 5 Loc [ Temp_C ]
4: 1.0 Mult
5: 0 Offset

5: Z=X+F (P34)
1: 5 X Loc [ Temp_C ]
2: 273.15 F
3: 6 Z Loc [ Temp_K ]

;Output data to final storage every 60 minutes

6: If time is (P92)
1: 0 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 10 Set Output Flag High (Flag 0)

7: Real Time (P77)
1: 0220 Day,Hour/Minute (midnight = 2400)

8: Average (P71)
1: 6 Reps
2: 1 Loc [ CM3_up ]

Copy range code options from example 1 here:

* Proper entries….
* Proper entries will vary with program and input channel usage.

** 25 mV range for CR10X, 50 mV for 21X and CR7
*** 4200 mV for 21X and CR7, 2100 mV for CR10X
+ 25 mV range for CR10X, 50 mV for 21X and CR7
++ 7.5 mV range for CR10X, 5 mV for 21X and CR7

7. Calibration

22

The CNR1 should be recalibrated every two years, or as an alternative, by
letting a higher standard run parallel to it over a two-day period and then
comparing the results. For comparison of pyranometers, one should use a clear
day. For comparison of pyrgeometers, one should compare nighttime results.
Deviations of more than 6% can be used to correct the calibration factors.

8. Troubleshooting

If there is no clue as to what may be the problem, start performing the
following "upside-down test", which is a rough test for a first diagnosis. It can
be performed both outdoors and indoors. Indoor s, a lamp can be used as a
source for both Solar and Far Infrared radiation. Outdoors one should
preferably work with a solar elevation of more than 45 degrees (45 degrees
above horizon) and of course under stable conditions (no large changes in solar
irradiance, preferably cloudless).

1. Measure the radiation outputs in the normal position. Record the
measured values when the signals have stabilized, i.e. after about three
minutes.

2. Rotate the instrument 180 degrees, so that the upper and the lower sensors
are now in the reverse orientation as to the previous position.

3. Measure the radiation outputs once more. Record the measured values
when the radiometers have stabilized.

4. Since of the all sensors are trimmed, the values in the rotated position
should be equal in magnitude, only differing in sign. In a rough test like
this, deviations of +/- 10 % can be tolerated. If deviations greater than
this are encountered, the following tests might help.

CNR1 Net Radiometer

8.1 Testing the CM3

As a first test we recommend that one check the sensor impedance. It should
have a nominal value as indicated in the specifications. Zero, or infinite
resistance, indicates a failure in hardware connection.

Before starting the second test measurement, let the CM3 rest for at least five
minutes to let it regain its thermal equilibrium. For testing, set a voltmeter to
its most sensitive range setting. Darken the sensor. The signal should read
zero. Bear in mind that the response takes about one minute. Small deviations
from zero are possible; this is caused by thermal effects like touching the
pyranometer with your hand. The latter effect can be demonstrated by
deliberately heating the CM3 with your hand. Another cause migh t be the zero
offset of the amplifier. When this is the case, the same offset will also be
present when the amplifier is short-circuited with a 200 Ohm resistor. This is
an amplifier error. This amplifier error should not be larger than 5 Watts per
square meter. If the amplifier error is within specifications, proceed with the
third test.

In the third test the sensor should be exposed to light. The signal should be a
positive reading. Set the voltmeter range in such a way that the expected full­scale output of the pyranometer is within the full-scale input range of the
voltmeter. The range can be estimated on theoretical considerations. (When
the maximum expected radiation is 1500 Watts per square meter, which is
roughly equal to normal outdoor daylight conditions, and the sensitiv ity of the
pyranometer is 15 mV per Watt per square meter, the expected output range of
the pyranometer is 1500 times 15 which is equal to 22500 mV, or 0.0225
Volts). One can calculate the radiation intensity by dividing the pyranometer
output (0.0225 volts) by the calibration factor (0.000015 volt per watt per
square meter). Still no faults found? Your pyranometer is probably doing fine.

23

CNR1 Net Radiometer

8.2 Testing of the CG3

8.3 Testing the Pt-100

It is assumed that the amplifier circuit is the same as the one used for the CM3,
and that its zero offset is no more than a few watts per square meter, let us say
5 Watts per square meter just as an example (see second test in 7.1).

The pyrgeometer, the mounting plate, and ambient air should be at the same
temperature as much as possible. Let the CG3 rest for at least five minutes to
regain its thermal equilibrium. Set the voltmeter to its most sensitive range.
To test if the CG3 is working properly, we suggest putting your hand in front
of the CG3. The thermal radiation will cause CG3 to generate a positive
voltage when the hand's surface temperature is higher than the pyrgeometer
temperature. The CG3 will generate a negative voltage if the hand is colder.
The signal is proportional to the temperature difference (see the rule of thumb
of Section 4.5). The radiation that is emitted by the hand can be calculated by
dividing the pyrgeometer output by the calibration factor, and subsequently
correcting for the temperature, according to Equation 4.2. Still no faults
found? Your pyrgeometer is probably doing fine.

Using a meter which measures resistance, check the operation of the Pt-100. If
connected properly, the resistance of two opposite wires of the Pt-100 should
measure about 100 ohms (this includes the cable resistance for the standard 10­meter cable). The cable resistance should measure about 0.1 ohms per meter
cable.

24

Appendix A. CNR1 Performance and Measurements under Different Conditions

Below, Table A-1, shows an indication of what one might typically expect to
measure under different meteorol ogical c on ditions.

The first parameter is day and night. At night, the Solar radiation is zero. The
second column indicates if it is cloudy or clear. A cloud acts like a blanket,
absorbing part of the Solar radiation, and keeping Net Far Infrared radiation
close to zero. The third parameter is ambient temperature. This is included to
show that the "sky temperature" (column nine) tracks the ambient temperature.
Under cloudy conditions this is logical; cloud bases will be colder than the
ambient temperature at instrument level, the temperature difference depends
roughly on cloud altitude.

Under clear sky conditions it is less obvious that sky temperature "adjusts" to
the ambient temperature. This can roughly be attributed to the water vapor in
the air, which is a major contributor to the Far Infrared radiation.

It is assumed that when ambient temperature varies, the Net Far Infrared
radiation remains roughly the same, independent of ambient temperature. The
resulting measured values of the CG3's and CM3's are stated in columns 4 to 7.
These are indicative figures only, they depend strongly on other circumstances;
the CG3 results, of course, change with the sensor temperature. This is
indicated in column 8. During the day, the Pt-100 reading may rise due to
solar heating, up to 10 degrees above ambient temperature. During the night,
the sensor temperature may be lower than the ambient temperature due to Far
Infrared radiative cooling. The latter two effects do not influence the end result
of the calculations of Sky T and ground T. Therefore they are not taken into
account in the table. Actually in column 4 one might expect to see "0 to -50"
for all positions that are showing "0", in column 5 the "0" values may in reality
be "-20 to +20". The resulting sky temperature is indicated in column 9.
Under cloudy conditions this sky temperature is equal to ambient temperature.
Under clear conditions the sky temperature is lower than the ambient
temperature.

The ground temperature in column 10 is assumed to be equal to the ambient
temperature. In practice it may be higher during the day, due to solar heating.
Ground temperature may be lower than ambient during the night, due to Far
Infrared radiative cooling. The sky and the ground temperature can be
calculated from the measured values of the sensors using Equations 4.6 and

4.7.

A-1

Appendix A. CNR1 Performance and Measurements under Different Conditions

TABLE A-1. Typical output signals of CNR1 under different meteorological conditions.

Explanation can be found in the text.

Day

night

d cloud 20 0 0 0-500 0-150 20 20 20

d cloud -20 0 0 0-500 0-150 -20 -20 -20

d clear 20 -100* 0 0-1300 0-400 20 1* 20

d clear -20 -100* 0 0-1300 0-400 -20 -53* -20

n cloud 20 0 0 0 0 20 20 20

n cloud -20 0 0 0 0 -20 -20 -20

n clear 20 -100*** 0 0** 0 20 1*** 20

n clear -20 -100*** 0 0** 0 -20 -53*** -20

Cloudy

clear

+20 ºC

- 20 ºC

CG3

Up

CG3

low

CM3

up

CM3

low

Pt 100 sky T

ground

* Values may suffer from the so-called window heating offset; the sun heats
the pyrgeometer window causing a measurement error of + 25 Watts per square
meter (maximum).

** Values may suffer from negative Infrared offsets, caused by cooling off of
the CM3 dome by Far Infrared radiation. The maximum expected offset value
is 15 Watts per square meter.

T

*** Values may suffer from dew deposition. This causes the CG3-up values to
rise from -100 to 0 Watts per square meter.

A-2

Appendix B. Details about Using the Heater

NOTE

Whenever the heater is used, the heating may cause errors in the
measurement of the sensor temperature, see chapter 1.1.2.3. in
the Kipp and Zonen CNR1 manual
(http://www.kippzonen.com/?download/85182/CNR+1+Net+Ra

diometer+-+Manual+(English).aspx), two degrees typical, and

zero offsets in the CM3 (10 Watts per square meter typical).
Under most conditions the accuracy that is gained by heating will
be larger than the errors that are introduced by heating.

In both the CM3 and CG3, thermal sensors are used. These sensors in principle
measure a heat flow. For optimal performance, these sensors should be at
equilibrium with the ambient air. Heating the sensor disturbs this equilibrium.
This will give rise to zero offsets particularly in the CM3. A typical value
under conditions with no wind is 10 Watts per square meter. Therefore heating
should only be done if absolutely necessary. CG3 is less sensitive to this.
Offset values for CG3 cannot be determined, and therefore are not specified.

B.1 General Information

There is one major reason for heating: avoiding water deposition on the CG3
window and on the CM3 dome. In case of dew deposition on the CG3
window, the dew will ultimately obstruct the Far Infrared radiation completely,
causing a signal close to zero. In the case of rain, this will probably not lead to
significant errors, because with an overcast sky the signal is close to zero
anyway. The case of dew deposition is far more significant. Dew deposition
will probably take place under conditions with large Far Infrared irradiation
from the pyrgeometer detector to the clear sky, typically minus (-) 100 Watts
per meter square. Under conditions where cl ou ds o r wi n d are present, dew is
less likely to occur. A situation where dew depositing on the window of the
CG3, causing a signal of -100 Watts per square meter to drop to zero, is
certainly significant. If heating can avoid this, it certainly should be done
because all errors that are described above are much smaller than the gain in
accuracy of 100 Watts per meter square.

B-1

Appendix B. Details about Using the Heater

For decisions about heating one can make the following diagram:

Not available

12 VDC, 6 VA available?

Clock and relay available?

DO NOT HEAT

Available Consider options below

Not Available

DO NOT HEAT

(CSI recommendation)

Available

Heat from 1 hour before the sunset

until 1 hour after the sunset

The maximum allowable power for the heater is 50 VA. In case of snow or
frost one might also consider heating at a higher level than the usual 6 VA.
Heating at 20 VA will melt snow in most cases. 20 VA can be reached at 22
Volts. During high power heating, measurement accuracy cannot be specified.
You are advised to reject measured data readings during this high power
heating.

If lower voltage is available, one might consider heating at a lower power. The
6 VA is designed for extreme conditions. 2 VA is sufficient for moderate
conditions.

Time needed for reaching a stable instrument temperature when heating is used
is about 60 minutes.

B-2

Appendix C. CR3000/CR5000 Program that Controls the Heater

This program applies power to the CNR1 heater using the SW12V relay
controller and the pulse width modulation instruction (PWM ()).

The program below uses the dew point value. The datalogger calculates dew
point using the relative humidity (RH) measurements provided by the
HMP45C Temperature/Relative Humidity probe. Enter 0 degrees C as the set
point for the heater when a temperature/RH probe is not used.

The algorithm turns the heater on/off at 4 Hz. The duty cycle of the pulse is
changed depending on how close the radiometer body temperature is to the
dew point temperature. At or below the dew point, the duty cycle is 100%. It
drops off linearly to 20% until the body temperature is 5 degrees C above the
dew point. For body temperatures greater than 5 degrees C above the dew
point, the duty cycle continue to drop linearly, but with a different slope, until
0% at 33 degrees C above the dew point. If necessary, the user can change the
two duty-cycle slope transitions.

'CR3000 or CR5000 Series Datalogger

'CR3000 Series Datalogger

'Copyright (c) 2009 Campbell Scientific, Inc. All rights reserved.

'11 March 09
'version 0.0

'*** Wiring ***

'ANALOG INPUT
'5H HMP45C temperature signal (yellow)
'5L HMP45C signal reference (white)
'gnd HMP45C shield (clear)

'6H HMP45C relative humidity signal (blue)
'6L short jumper wire to 5L

'10H CNR1 Pt100 signal (red)
'10L CNR1 Pt100 signal reference (blue)
'gnd CNR1 Pt100 shield (silver)

'11H CNR1 downwelling shortwave radiation signal (red)
'11L CNR1 downwelling shortwave radiation signal reference (blue)
'gnd CNR1 shield (silver)

'12H CNR1 upwelling shortwave radiation signal (white)
'12L CNR1 upwelling shortwave radiation signal reference (green)

'13H CNR1 downwelling longwave radiation signal (brown)
'13L CNR1 downwelling longwave radiation signal reference (yellow)

C-1

Appendix C. CR3000/CR5000 Program that Controls the Heater

'14H CNR1 upwelling longwave radiation signal (purple or pink)
'14L CNR1 upwelling longwave radiation signal reference (gray)

'CURRENT EXCITATION
'IX1 CNR1 Pt100 current excitation (white)
'IXR CNR1 Pt100 current excitation reference (green)

'CONTROL PORTS
'C1 SW12V control (green)
'G SW12V control/power reference (black)

'POWER OUT
'12V HMP45C power (red)
' SW12V power (red)
'G HMP45C power reference (black)

'POWER IN
'12V datalogger (red)
'G datalogger (black)

'EXTERNAL POWER SUPPLY
'POS datalogger (red)
'NEG datalogger (black)

'SW12V Power Control Module
'SW12V NR 01 heater excitation (brown)
'G NR 01 heater excitation reference (yellow)

PipeLineMode

'*** Constants ***

Const NR01_SHORT_DW_CAL = 1000/13.41 'Unique NR 01 shortwave downwelling multiplier (1000/15.5).
Const NR01_SHORT_UW_CAL = 1000/13.93 'Unique NR 01 shortwave upwelling multiplier (1000/13.5).
Const NR01_LONG_DW_CAL = 1000/8.8 'Unique NR 01 longwave downwelling multiplier (1000/10.5).
Const NR01_LONG_UW_CAL = 1000/9.4 'Unique NR 01 longwave upwelling multiplier (1000/10.3).

Const MAX_DUTY_CYCLE_1 = 1
Const MAX_DUTY_CYCLE_2 = 0.2
Const DELTA_SET_POINT_1 = 5
Const DELTA_SET_POINT_2 = 28
Const SLOPE_1 = (MAX_DUTY_CYCLE_2-MAX_DUTY_CYCLE_1)/DELTA_SET_POINT_1
Const SLOPE_2 = (-MAX_DUTY_CYCL E_2)/DELTA_SET_POINT_2

'*** Variables ***

Public no_heat_flag As Boolean 'Turn off heater control when TRUE.
Public panel_temp 'Datalogger panel temperature.
Public batt_volt 'Datalogger battery voltage.
Public hmp(2) 'HMP45C temperature and relative humidity.
Alias hmp(1) = t_hmp 'HMP45C temperature.
Alias hmp(2) = rh_hmp 'HMP45C relative humidity.
Public e_hmp 'HMP45C vapor pressure.
Public nr01(9) 'NR 01 net radiometer.
Alias nr01(1) = Rn
Alias nr01(2) = albedo

C-2

Appendix C. CR3000/CR5000 Program that Controls the Heater

Alias nr01(3) = Rs_downwell
Alias nr01(4) = Rs_upwell
Alias nr01(5) = Rl_downwell
Alias nr01(6) = Rl_upwell
Alias nr01(7) = t_nr01
Alias nr01(8) = Rl_down_meas
Alias nr01(9) = Rl_up_meas
Units panel_temp = C
Units batt_volt = V
Units t_hmp = C
Units rh_hmp = percent
Units e_hmp = kPa
Units nr01 = W/m^2
Units albedo = unitless
Units t_nr01 = K

'Net radiometer heater control variables.

Public set_point_temperature
Public duty_cycle

'Working Variables

Dim scratch_out(3)
Alias scratch_out(1) = t_hmp_mean
Alias scratch_out(2) = e_hmp_mean
Alias scratch_out(3) = e_sat_hmp_mean
Dim rh_hmp_mean 'Mean HMP45C relative humidity.
Dim t_dew_hmp_mean 'Mean dew point temperat ure.
Dim e_sat_hmp 'HMP45C saturation vapor pressure.
Units t_hmp_mean = C
Units e_hmp_mean = kPa
Units e_sat_hmp_mean = kPa
Units rh_hmp_mean = percent
Units t_dew_hmp_mean = C

DataTable (stats,TRUE,-1)
DataInterval (0,5,Min,10)

Sample (1,t_hmp_mean,IEEE4)
Sample (1,e_hmp_mean,IEEE4)
Sample (1,rh_hmp_mean,IEEE4)
Sample (1,t_dew_hmp_mean,IEEE4)
Sample (1,duty_cycle,IEEE4)
Average (9,Rn,IEEE4,FALSE)
EndTable

DataTable (scratch,TRUE,1)
TableHide
DataInterval (0,5,Min,10)

Average (1,t_hmp,IEEE4,FALSE)
Average (1,e_hmp,IEEE4,FALSE)
Average (1,e_sat_hmp,IEEE4,FALSE)
EndTable

C-3

Appendix C. CR3000/CR5000 Program that Controls the Heater

BeginProg
Scan (1,Sec,0,0)

'Control the net radiometer heater.

PWM (duty_cycle,4,250,mSec)

'Datalogger panel temperature.

PanelTemp (panel_temp,250)

'Measure battery voltage.

Battery (batt_volt)

'Measure the HMP45C temperature and relative humidity.

VoltDiff (t_hmp,1,mV1000C,5,TRUE,200,250,0.1,-40)
VoltDiff (rh_hmp,1,mV1000C,6,TRUE,200,250,0.1,0)

'Measure NR 01 Net Radiometer.

Resistance (t_nr01,1,mV200,10,Ix1,1,1675,TRUE,TRUE,200,250,1,0)
VoltDiff (Rs_downwell,1,mV20C,11,TRUE,200,250,NR01_SHORT_DW_CAL,0)
VoltDiff (Rs_upwell,1,mV20C,12,TRUE,200,250,NR01_SHORT_UW_CAL,0)
VoltDiff (Rl_down_meas,1,mV20C,13,TRUE,200,250,NR01_LONG_DW_CAL,0)
VoltDiff (Rl_up_meas,1,mV20C,14,TRUE,200,250,NR01_LONG_UW_CAL,0)

'Find the HMP45C vapor pressure and saturation vapor pressure (kPa).

VaporPressure (e_hmp,t_hmp,rh_hmp)
SatVP (e_sat_hmp,t_hmp)

'Compute net radiation, albedo, downwelling and upwelling longwave radiation.

t_nr01 = t_nr01/100
PRT (t_nr01,1,t_nr01,1,273.15)

Rn = Rs_downwell-Rs_upwell+Rl_down_meas-Rl_up_meas
albedo = Rs_upwell/Rs_downwell
Rl_downwell = Rl_down_meas+(5.67e-8*t_nr01*t_nr01*t_nr01*t_nr01)
Rl_upwell = Rl_up_meas+(5.67e-8*t_nr01*t_nr01*t_nr01*t_nr01)

CallTable (scratch)
If ( scratch.Output(1,1) ) Then
GetRecord (scratch_out(1),scratch,1)
rh_hmp_mean = 100*e_hmp_mean/e_sat_hmp_mean
DewPoint (t_dew_hmp_mean,t_hmp_mean,rh_hmp_mean)

'Control the NR 01 heater using 4 Hz pulse width modulation. Below the dew
' point temperature applies 100% power. Above the dew point, power is reduced
' linearly to 20% until the dew point plus DELTA_SET_POINT_1. After the dew
' point plus DELTA_SET_POINT_1 and until the dew point plus
' DELTA_SET_POINT_2 plus DELTA_SET_POINT_2, the power is reduced linearly to 0%.

If ( (t_nr01 <> NaN) AND (t_dew_hmp_mean <> NaN) AND (no_heat_flag <> TRUE) ) Then
set_point_temperature = t_dew_hmp_mean+273.15
Select Case t_nr01
Case Is < ( set_point_temperature )
duty_cycle = 1
Case Is < ( set_point_temperature+DELTA_SET_POINT_1 )
duty_cycle = MAX_DUTY_CYCLE_1+(t_nr01-(t_dew_hmp_mean+273.15))*SLOPE_1
Case Is < ( set_point_temperature+DELTA_SET_POINT_1+DELTA_SET_POINT_2 )
duty_cycle = MAX_DUTY_CYCLE_2+(t_nr01-
(t_dew_hmp_mean+273.15+DELTA_SET_POINT_1))*SLOPE_2

C-4

Appendix C. CR3000/CR5000 Program that Controls the Heater

Case Else
duty_cycle = 0.01
EndSelect
Else
duty_cycle = 0.01
EndIf
EndIf

CallTable (stats)
NextScan
EndProg

C-5

Appendix C. CR3000/CR5000 Program that Controls the Heater

C-6

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