Campbell Scientific NR-LITE-L User Manual

NR-LITE Net Radiometer
Revision: 5/10
Copyright © 1998-2010
Campbell Scientific, Inc.

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. The following contact information is for US and International customers residing in countries served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs for customers within their territories. Please visit www.campbellsci.com to determine which Campbell Scientific company serves your country.
To obtain a Returned Materials Authorization (RMA), contact CAMPBELL SCIENTIFIC, INC., phone (435) 753-2342. After an applications engineer determines the nature of the problem, an RMA number will be issued. Please write this number clearly on the outside of the shipping container. 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 repair@campbellsci.com 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
NR-LITE 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
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 Input Range and Integration ......................................................................9
5.2 Calibration Factor......................................................................................9
5.3 Example Programs...................................................................................10
5.3.1 CR3000 Example Program without Wind Speed Correction ........10
5.3.2 CR1000 Example Program with Wind Speed Correction..............11
5.3.3 CR10(X) Example Program without Wind Speed Correction.......12
5.3.4 CR10X Example Program with Wind Speed Correction...............13
6. Maintenance................................................................15
7. Troubleshooting .........................................................15
7.1 Checking Sensor Operation.....................................................................15
7.2 Radiometer produces no apparent output................................................16
7.3 Readings are not as expected...................................................................16
Figures
1. NR-LITE’s Components and Dimensions (in millimeters)........................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. Mounting the NR-LITE onto a pole (top) and crossarm (bottom) via
the 26120 Mounting Kit.........................................................................7
7. NR-Lite to Datalogger Connections...........................................................8
i
NR-LITE Table of Contents
Tables
1. Datalogger Connections for Differential Measurement............................. 8
2. Datalogger Connections for Single-Ended Measurement.......................... 8
ii

NR-LITE Net Radiometer

k
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 stic
16 x 800 Support Arm
80
Bubble level indicator
FIGURE 1. NR-LITE’s Components and Dimensions (in millimeters)
Support arm
Adjustable mounting arm
The NR-LITE is used for measuring solar a n d far i nf rared 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.
-2
).
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.
2
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
FIGURE 3. Approximate Spectral Sensitivity and Solar/F.I.R. Radiation
The upwards facing sensor is calibrated for solar radiatio n wavel e ngths. 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
+ 15 hidden pages