Campbell NR-Lite User manual

NR-LITE NET RADIOMETER
INSTRUCTION MANUAL
REVISION: 11/03
COPYRIGHT (c) 1998-2003 CAMPBELL SCIENTIFIC, INC.

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Warranty and Assistance
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.
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]

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i
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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1
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
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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-2).
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.

NR-LITE Net Radiometer
2
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.

NR-LITE Net Radiometer
3
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.

NR-LITE Net Radiometer
4
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.