Campbell NR-Lite Manuel utilisateur

NR-LITE NET RADIOMETER

INSTRUCTION MANUAL

REVISION: 11/03

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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 (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

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 (435) 753-2342

FAX (435) 750-9540

www.campbellsci.com

Campbell Scientific Canada Corp.

11564 -149th Street

Edmonton, Alberta T5M 1W7

CANADA

Phone (780) 454-2505

FAX (780) 454-2655

Campbell Scientific Ltd.

Campbell Park

80 Hathern Road

Shepshed, Loughborough

LE12 9GX, U.K.

Phone +44 (0) 1509 601141

FAX +44 (0) 1509 601091

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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 Ad

ustable mountin

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-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

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

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

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.

Table des matières

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