Campbell NR-Lite Instruction Manual

NR-LITE NET RADIOMETER

INSTRUCTION MANUAL

REVISION: 11/03

COPYRIGHT (c) 1998-2003 CAMPBELL SCIENTIFIC, INC.

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Warranty and Assistance

815 W. 1800 N.
Logan, UT 84321-1784
USA
Phone [phone]
FAX [phone]
www.campbellsci.com

Campbell Scientific Canada Corp.
11564 -149th Street
Edmonton, Alberta T5M 1W7
CANADA
Phone [phone]
FAX [phone]

Campbell Scientific Ltd.
Campbell Park
80 Hathern Road
Shepshed, Loughborough
LE12 9GX, U.K.
Phone [phone]
FAX [phone]

The NR-LITE 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. 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

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

Non-warranty products returned for repair should be accompanied by a
purchase order to cover the repair.

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NR-LITE Table of Contents

1. General Description ....................................................1

1.1 Electrical Properties..................................................................................2

1.2 Spectral Properties ....................................................................................2

1.3 Directional/Cosine Response....................................................................3

1.4 Sensitivity to Wind Speed.........................................................................4

2. Sensor Specifications ................................................5

3. Installing the NR-LITE.................................................6

4. Wiring ..........................................................................8

5. Datalogger Programming...........................................9

5.1 Datalogger Input Range Codes .................................................................9

5.2 Calibration Factor .....................................................................................9

5.3 Example Programs....................................................................................9

5.3.1 Example 1, CR10/10X Program without Wind Speed Correction ..9

5.3.2 Example 2, CR10/10X Program with Wind Speed Correction .....10

6. Maintenance..............................................................12

7. Troubleshooting........................................................12

7.1 Checking Sensor Operation .....................................................................12

7.2 Radiometer produces no apparent output................................................13

7.3 Readings are not as expected ..................................................................14

Figures

1. General View and Dimensions of NR-LITE...............................................1

2. Electrical Circuit for the NR-LITE Net Radiometer ...................................2

3. Approximate Spectral Sensitivity and Solar/F.I.R. Radiation.....................3

4. Cosine Response of a Typical Net Radiometer...........................................4

5. NR-LITE Wind Sensitivity .........................................................................5

6. NR-LITE Mounting Options.......................................................................7

7. NR-Lite to Datalogger Connections............................................................8

Tables

1. Datalogger Connections for Differential Measurement ..............................8

2. Datalogger Connections for Single-Ended Measurement ...........................8

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NR-LITE Net Radiometer

The NR-LITE is a high-output thermopile sensor which measures the algebraic sum of
incoming and outgoing all-wave radiation (i.e. both short-wave and long-wave
components). Incoming radiation consists of direct (beam) and diffuse solar radiation plus
long-wave irradiance from the sky. Outgoing radiation consists of reflected solar radiation
plus the terrestrial long-wave component.

The NR-LITE is equipped with Teflon-coated sensor surfaces. This results in a robust
design which gives very easy maintenance and good sensor stability. However, this design
is slightly less accurate than the more traditional radiometers which use plastic domes.

1. General Description

Bird repelling stick

∅16 x 800 Support Arm

∅80

Bubble level indicator

Adjustable mounting arm

FIGURE 1. General View and Dimensions of NR-LITE

The NR-LITE is used for measuring solar and far infrared radiation balance.
This balance is known as the net (total) radiation. Its upwards facing sensor
measures the solar energy and far infra-red energy that is received from the
entire hemisphere (180° field of view). Its downwards facing sensor measures
the energy received from the surface of the soil. The two readings are
automatically subtracted and the result converted to a single output signal. This
output represents the net radiation, (which can be interpreted as meaning the
radiative energy that is seen at the surface) and is expressed in Watts per square
meter (W m

The NR-LITE is designed for continuous outside use. The sensor surfaces are
coated with Teflon. This ensures good sensor stability, very long life and easy
maintenance compared to the more usual radiometers fitted with plastic domes.
However, it does have some disadvantages, particularly a higher sensitivity to
wind speed with a subsequent lessening of accuracy. It is, though, possible to
correct for the wind speed sensitivity if the sensor is installed in a system
where wind speed is also being measured.

Although net radiometers are usually used in meteorology to measure radiation
balance, the NR-LITE can also be used to measure indoor climate radiative
stress.

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).

1

NR-LITE Net Radiometer

1.1 Electrical Properties

The thermopile consists of a number of thermocouples connected in series,
essentially providing a highly sensitive differential temperature sensor. The
thermopile generates a voltage output – the sensor itself is passive, and so no
power supply is required.

The upwards and downwards facing sensor surfaces are connected to the upper
and lower thermopile junctions respectively, and so the sensor can measure the
differential temperature. This temperature differential can be measured to a
high accuracy (in the order of 0.001 degrees), and is proportional to the net
radiation.

The thermopile determines the electrical characteristics of the instrument. Both
upper and lower facing sensors have a field of view of 180 degrees, and their
angular characteristics conform closely to the so-called ‘cosine’ response (see
following sections).

The electrical sensitivity for the thermopile changes with temperature, and no
nominal sensitivity value is available.

FIGURE 2. Electrical Circuit for the NR-LITE Net Radiometer

1.2 Spectral Properties

The spectral properties of the NR-LITE are determined by the Teflon surface
of the sensors. An approximate spectral sensitivity response curve for the
instrument combined with the spectrum of the sun under a clear sky, and the
spectrum of outgoing far infra-red radiation (F.I.R.) is shown in Figure 3,
below.

2

NR-LITE Net Radiometer

FIGURE 3. Approximate Spectral Sensitivity and Solar/F.I.R. Radiation

The upwards facing sensor is calibrated for solar radiation wavelengths. The
following assumptions are made:

• It is assumed that the downwards facing sensor has the same sensitivity.

However, since the two sensors may not be perfectly symmetrical, this
assumption may not always be true, but any differences are small.

• It is also assumed that the NR-LITE’s sensitivity is the same for both solar

and infrared radiation.

1.3 Directional/Cosine Response

The measurement of the radiation falling on a surface (also known as
irradiance or radiative flux) is based on two assumptions:

1. The sensor surface is spectrally black - i.e. that it absorbs all radiation

from all wavelengths (see section above).

2. That it has a true field of view of 180°.

These two properties, taken together, with which the net radiometer needs to
comply, are generally known as the ‘cosine response’.

A perfect cosine response will show maximum sensitivity at an angle of
incidence of zero degrees (perpendicular to the sensor surface) and zero
sensitivity at an angle of incidence of 90 degrees (radiation passing over the
sensor surface). At any angle between 0 and 90 degrees the sensitivity should
be proportional to the cosine of the angle of incidence.

Figure 4 shows the behavior of a typical net radiometer. The vertical axis
shows the deviation from ideal behavior, expressed in percentage deviation
from the ideal value.

3

NR-LITE Net Radiometer

FIGURE 4. Cosine Response of a Typical Net Radiometer

1.4 Sensitivity to Wind Speed

The calibration of the NR-LITE is carried out at zero wind speed. At any other
wind speed the sensitivity will decrease. It has been shown that this decrease in
sensitivity is less than 1% of reading per meter per second wind speed, and the
effect is essentially independent of the radiation level.

Net radiation readings can be corrected for wind speed sensitivity using the
following equation, which was developed by Jerry Brotzge at the Oklahoma
Climate Survey:

Wind Sensitivity equation for the NR-LITE:

Rn,cor = Rn,obs U < 5 m/s
Rn,cor = Rn,obs ∗ (1.0+A ∗ (U-5.0)) U > 5 m/s

Where,

Rn,cor = Net radiation corrected for wind speed
Rn,obs = Net radiation not corrected for wind speed
U = Horizontal wind speed in m/s
A = empirical constant derived from data = 0.021286

The following scatter plots illustrate the wind sensitivity for both the NR-LITE
and CNR1 net radiometer models.

4

NR-LITE Net Radiometer

2. Sensor Specifications

Spectral

Spectral range: 0.2 to 100 µm
Detector type: Thermopile
Detector protection: Teflon coating
Detector profile: Conical

Directional

Directional error:
(0 - 60° at 1000 W m
Sensor asymmetry: ±5% typical, (±10% worst case).

FIGURE 5. NR-LITE Wind Sensitivity

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): <30 W m

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5

NR-LITE Net Radiometer

Mechanical

Housing material: Anodized aluminum
Cable material: Polyurethane
Weight: 200 g
Cable length: 15 m (can be extended up to 100 m)
Physical Dimensions

Sensor: 3.1” (8.0 cm) diameter
Support Arm: 0.6” (1.6 cm) diameter x 31.5” (80 cm) L

Weight: 23 oz (635 g)

Environmental

Working temperature: -30 to +70°C
Temperature dependence: 0.12%/°C

3. Installing the NR-LITE

Mount the sensor so that no shadow 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. In the northern hemisphere the instrument is normally oriented
towards the South to avoid potential problems from shading. The downward
facing sensor is representative (99%) for a circular area having a radius of ten
times the height (10h).

NOTE

To avoid shading effects and to promote spatial averaging the NR-LITE should
be mounted at least 1.5 m above the ground surface. It is recommended that
the NR-LITE be mounted to a separate vertical pipe at least 25’ from any other
mounting structures. PN 14264 mounting bracket is used to mount the NR­LITE directly to a vertical pipe, or to a UT108 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. The hole through PN
14264 has two different diameters to accommodate different models of
sensors. The NR-LITE mounts through the larger diameter hole that
extends half way through the bracket.

2. Feed the sensor cable through the larger diameter hole in the mounting
bracket, followed by the mounting arm of the sensor. Tighten the two set
screws just enough to secure the mounting arm position, but loose enough
to be rotated.

Do not attempt to rotate the instrument using the sensor head or
you may damage the sensor – 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.

6

NR-LITE Net Radiometer

N

14264 Mounting Bracket

R-LITE

UT018 Crossarm

14264 Mounting Bracket

NR-LITE

FIGURE 6. NR-LITE Mounting Options

7

NR-LITE Net Radiometer

r

4. Wiring

The NR-LITE can be measured with a differential or single-ended channel on
the datalogger; a differential channel is recommended.

White Radiation Signal

Green Signal Reference

(User supplied jumper wire for differential measurement only)

Clea

FIGURE 7. NR-Lite to Datalogger Connections

TABLE 1. Datalogger Connections for Differential Measurement

Function Color CR10X,CR510 CR23X 21X/CR7

Radiation Signal White Differential H Differential H Differential H

Signal Reference Green Differential L Differential L Differential L

Jumper to AG

Shield Clear G

TABLE 2. Datalogger Connections for Single-Ended Measurement

Function Color CR10X,CR510 CR23X 21X/CR7

Radiation Signal White S.E. Channel S.E. Channel S.E. Channel

Signal Reference Green AG

Shield Clear G

Shield

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5. Datalogger Programming

The NR-LITE outputs a low-level voltage ranging from 0 to a maximum of
about 15 mV. A differential voltage measurement (Instruction 2) is
recommended because it has better noise rejection than a single-ended
measurement. If a differential channel is not available, a single-ended
measurement (Instruction 1) can be used. The acceptability of a single-ended
measurement can be determined by simply comparing the results of single­ended and differential measurements made under the same conditions.

5.1 Datalogger Input Range Codes

Normally the 15 mV range for the 21X and CR7, the 25 mV range for the
CR10(X) and CR500/CR510, and the 50 mV range for the CR23X are suitable.

The parameter code for the input range also specifies the measurement
integration time. The slow or 60 Hz rejection integration gives a more noise­free reading. A fast integration takes less power and allows for faster
throughput.

NR-LITE Net Radiometer

5.2 Calibration Factor

Each NR-LITE is provided with a ‘Certificate of Calibration’ by the
manufacturer which shows the sensor serial number and a ‘sensitivity’ or
calibration factor. This calibration factor, after conversion, is used in the
datalogger program. Always cross check to ensure that the serial number of
your NR-LITE and the number on the calibration certificate are identical. The
serial number and sensitivity are also shown on a small label attached to the
connecting arm near the head of the sensor itself.

The calibration factor provided by Kipp & Zonen is in units of uV/(W m
which needs to be converted to units of (W m
parameter in the datalogger program. To convert the units, divide the
calibration factor into 1000. For example, if the calibration factor is 15.8
uV/(W m

1000/15.8 = 63.29 (W m

-2

), the multiplier is:

-2

)/mV

-2

)/mV for the multiplier

5.3 Example Programs

5.3.1 Example 1, CR10(X) Program without Wind Speed Correction

Shown below is an example program written for the CR10(X) datalogger. The
datalogger measures the output from the sensor every 60 seconds and outputs
the average net radiation every hour.

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),

The calibration factor used will only apply for one specific sensor. A new value
will need to be calculated for every different sensor based on the certificate of
calibration for that sensor (see above).

9

NR-LITE Net Radiometer

;{CR10X}
;
*Table 1 Program

01: 60 Execution Interval (seconds)

1: Volt (DIFF) (P2)

1: 1 Reps
2: 3** 25 mV Slow Range ;range code for CR10(X) datalogger
3: 1* DIFF Channel
4: 1* Loc [ Net_rad ]
5: 63.29 Mult ;Multiplier for specific sensor
6: 0.0 Offset ;in units of (W m-2)/mV (see above)

2: 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)

Wiring for Example 1

Example CR10X

Program Channels

Color Function

White Radiation Signal 1H
Green Signal Reference 1L

Jumpered to AG

Clear Shield G

Used

3: Real Time (P77)

1: 110 Day,Hour/Minute (midnight = 0000)

4: Average (P71)

1: 1 Reps
2: 1 Loc [ Net_rad ]

5.3.2 Example 2, CR10X Program with Wind Speed Correction

Example 2 measures the NR-LITE using a Single-Ended input and Instruction

1. The program also measures wind speed and applies the correction factor as

described in Section 1.4. Average net radiation and wind speed are output
every hour.

Wiring for Example 2

Example CR10X

Program Channels

Color Function

White Radiation Signal S.E. Channel 1
Green Signal Reference AG

Clear Shield G

Used

10

NR-LITE Net Radiometer

;{CR10X}
;
*Table 1 Program
01: 60 Execution Interval (seconds)

;measure 05103 wind speed

1: Pulse (P3)

1: 1 Reps
2: 1 Pulse Channel 1
3: 21 Low Level AC, Output Hz
4: 1 Loc [ Wspd_m_s ]
5: .0980 Mult
6: 0 Offset

;measure NR-LITE net radiation

2: Volt (SE) (P1)

1: 1 Reps
2: 3** 25 mV Slow Range
3: 1* SE Channel
4: 2* Loc [ Rn_obs ]
5: 63.29 Mult ;Multiplier for specific sensor
6: 0 Offset ;in units of (W m-2)/mV (see above)

;apply wind speed correction factor
;Rn,cor = Rn,obs*(1.0+0.021286*(U-5.0)) when U > 5 m/s

3: If (X<=>F) (P89)

1: 1 X Loc [ Wspd_m_s ]
2: 3 >=
3: 5 F
4: 30 Then Do

4: Z=X+F (P34)

1: 1 X Loc [ Wspd_m_s ]
2: -5 F
3: 24 Z Loc [ scratch_1 ]

5: Z=X*F (P37)

1: 24 X Loc [ scratch_1 ]
2: .021286 F
3: 25 Z Loc [ scratch_2 ]

6: Z=X+F (P34)

1: 25 X Loc [ scratch_2 ]
2: 1 F
3: 26 Z Loc [ scratch_3 ]

7: Z=X*Y (P36)

1: 26 X Loc [ scratch_3 ]
2: 2 Y Loc [ Rn_obs ]
3: 3 Z Loc [ Rn_cor ]

8: Else (P94)

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NR-LITE Net Radiometer

9: Z=X (P31)

1: 2 X Loc [ Rn_obs ]
2: 3 Z Loc [ Rn_cor ]

10: End (P95)

11: 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)

12: Real Time (P77)

1: 1220 Year,Day,Hour/Minute (midnight = 2400)

13: Average (P71)

1: 1 Reps
2: 3 Loc [ Rn_cor ]

14: Average (P71)

1: 1 Reps
2: 1 Loc [ Wspd_m_s ]

* Proper entries will vary with program and input channel assignments.
** 25 mV range for CR10(X) and CR510, the 50 mV range for CR23X, and the 15 mV range for

21X and CR7.

6. Maintenance

The radiometer is an ‘all weather’ instrument and is very stable, but should be
handled with care. It requires little periodic maintenance, apart from cleaning
the sensor surfaces carefully with a soft cloth using water or alcohol.

The NR-LITE should be recalibrated every two years. Contact CSI for an
RMA number before returning the sensor for recalibration.

7. Troubleshooting

7.1 Checking Sensor Operation

To effectively check the instrument’s operation, you will need:

1. The NR-LITE itself

2. A voltmeter, range 0 to 50 mV, with an input impedance greater than

5000 Ohms

12

3. A light source

4. A table or bench

Position the radiometer so that its downward facing sensor is about 10 mm
(0.4”) above a flat surface (table or bench), and the upwards facing sensor is
facing the light source (lamp). Do not touch the sensor head itself, as this will

NR-LITE Net Radiometer

introduce thermal shocks. Hold the instrument only by its mounting arm at all
times.

Follow the procedure outlined below:

• Connect the NR-LITE wires to the voltmeter. Connect the white wire to

the positive lead and the green wire to the negative lead.

• Select the most sensitive range on the voltmeter.

• With the lamp switched off, read the sensor output signal – allow a minute

or so for the signal to fully stabilize.

• Switch on the lamp. The sensor should now producer a higher positive

reading.

• Turn the lamp off again, when the signal should slowly return to its

original level, proving the sensor’s sensitivity to light.

• Turn the sensor upside down. The signal value should reverse in sign (i.e.

a +10 mV signal should become a –10 mV signal). Don’t worry if the two
values are not exactly the same (up to 10% difference) as the sensor
profiles can vary. After completing this test, return the sensor to its
original orientation and let it stabilize.

• Put your hand over the upper sensor. Assuming that your hand is at a

higher temperature than the sensor the positive reading should increase.
Conversely, if the sensor is warmer than your hand the reading will
decrease.

• Check the radiometer’s sensitivity to thermal shocks by touching the edge

of the sensor (the blank metal) with your hand for some seconds. The
resultant shock will result in a signal drift, or a zero offset that will take
some time to settle back to zero.

• Adjust the range of the voltmeter so that the expected full-scale output of

the radiometer is about the same as the range of the voltmeter. A
(theoretical ) way to calculate the maximum expected output for normal
meteorological applications is shown below:

Max. expected radiation +1500 W m

Min. radiation –200 W m

-2

Sensitivity of the net radiometer 10 µV/(W m-2)

Expected output range of the radiometer is (1500+200) x 10 =

1700 x 10 = 17.0 mV or 0.017 V.

7.2 Radiometer produces no apparent output

-2

If your net radiometer does not appear to be working at all, do the following
checks:

• Check the instrument’s sensitivity to radiation, following the procedure

shown in Section 7.1.

13

NR-LITE Net Radiometer

7.3 Readings are not as expected

• If this appears to produce no results, measure the impedance of the sensor

across the white and green wires. The impedance reading should be close
to 2.3Ω. If it is virtually zero, a short circuit is indicated. If it is ‘infinite’,

the thermopile is blown.

• Under full sunlight the expected radiation value is about 1000 W m-2.

Under lamps it may be greater. For indoor climate studies, smaller values
are to be expected unless solar radiation is present. A typical value for a
room when facing a wall and a relatively cold window is 50 W m

• Are you using the correct calibration factor? Note that this factor is unique

for each individual sensor as noted on the calibration certificate provided
with that sensor. Did you convert the factor to the correct value for the
datalogger program? (See Section 5, above).

• Check the datalogger program for errors.

If you cannot resolve your problems, please contact Campbell Scientific for
further advice.

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.

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