Campbell LI200X Manual de usuario

INSTRUCTION MANUAL

LI200X Pyranometer

Revision: 2/97

Campbell Scientific, Inc.

Warranty and Assistance

The LI200X PYRANOMETER 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

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

LI200X Table of Contents

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1. General........................................................................1

1.1 Specifications............................................................................................1

2. Installation...................................................................2

3. Wiring ..........................................................................2

4. Programming ..............................................................3

4.1 Average Solar Radiation ...........................................................................3

4.2 Total Solar Radiation................................................................................4

5. Maintenance................................................................6

6. Calibration...................................................................6

Appendix

Appendix A...................................................................A-1

A.1 LI200S Pyranometer ............................................................................A-1

A.1.1 Wiring ........................................................................................A-1

A.2 Unmodified Pyranometers....................................................................A-1

A.2.1 Wiring ........................................................................................A-1

A.3 Input Range..........................................................................................A-1

A.4 Multiplier .............................................................................................A-2

This is a blank page.

LI200X PYRANOMETER

1. GENERAL

The LI200X measures incoming solar radiation

with a silicon photovoltaic detector mounted in

cosine-corrected head. The detector outputs

current; a shunt resistor in the sensor cable

converts the signal from current to voltage,

allowing the LI200X to be measured directly by

Campbell Scientific dataloggers. The LI200X is

calibrated against an Eppley Precision Spectral

Pyranometer to accurately measure sun plus

sky radiation. Do not use the LI200X under

vegetation or artificial lights, because it is

calibrated for the daylight spectrum (400 to

1100 nm).

During the night the LI200X may read slightly

negative incoming solar radiation. This negative

signal is caused by RF noise. Negative values

may be set to zero in the datalogger program.

For more theoretical information on the silicon

photovoltaic detector see Kerr, J. P., G. W.

Thurtell, and C. B. Tanner: An integrating

pyranometer for climatological observer stations

and mesoscale networks. J. Appl. Meteor., 6,

688-694.

1.1 SPECIFICATIONS

Stability: < ±2% change over a 1

year period

Response Time: 10 µs

Cosine Correction: Cosine corrected up to 80°

Operating

Temperature: -40 to +65 °C

Temperature

Dependence: 0.15% per °C

Relative Humidity: 0 to 100%

Detector: High stability silicon

photovoltaic detector (blue

enhanced)

Sensor Housing: Weatherproof anodized

aluminum case with acrylic

diffuser and stainless steel

hardware

Size: 0.94" dia x 1.00" H (2.38 cm

dia x 2.54 cm H)

Weight: 1 oz. (28 g)

Accuracy: Absolute error in natural

daylight is ±5% maximum;

±3% typical

Sensitivity: 0.2 kW m-2 mV-1

Linearity: Maximum deviation of 1%

up to 3000 W m-2

Shunt Resistor: Adjustable, 40.2 to 90.2 Ω,

factory set to give the

above sensitivity

Light Spectrum

Waveband: 400 to 1100 nm

NOTE: The black outer jacket of the cable is

Santoprene® rubber. This compound was

chosen for its resistance to temperature

extremes, moisture, and UV degradation.

However, this jacket will support combustion

in air. It is rated as slow burning when tested

according to U.L. 94 H.B. and will pass

FMVSS302. Local fire codes may preclude

its use inside buildings.

FIGURE 1-1. LI200X Pyranometer

LI200X PYRANOMETER

2. INSTALLATION

To ensure accurate measurements, the LI200X

should be mounted using LI2003S base/leveling

fixture. This base incorporates a bubble level

and three adjustment screws. The LI200X and

base/leveling fixture are attached to a tripod or

tower using one of three mounting

configurations (see Figure 2-1 through 2-3).

The LI200X should be mounted such that it is

never shaded by the tripod/tower or other

sensors.

NOTE: Remove the red cap after installing

the sensor. Save this cap for shipping or

storing the sensor.

FIGURE 2-1. 015 Pyranometer Mounting Arm

FIGURE 2-2. 025 Crossarm Stand and

019ALU Crossarm

FIGURE 2-3. UTLI Leveling Fixture and

Crossarm Mount and UT018 Tower

Mounting Bracket and Crossarm

3. WIRING

Measure the LI200X with instruction Differential

Voltage (P2). A schematic diagram of the

LI200X is shown in Figure 3-1. The red lead is

connected to the high side (H) of any differential

channel. The black lead is connected to the

corresponding low (L) side of the differential

channel. On a CR10(X), the white lead is

connected an analog ground (AG) and clear to

ground (G). On a 21X the white and clear leads

are connected to ground (G).

If a 21X is used to measure the LI200X and

powers a 12 VDC sensor, the current drawn by

the 12 VDC sensor may cause a difference in

ground potential between the 21X ground

terminals and the reference ground point in the

datalogger. This ground potential results in an

offset on single ended measurements. This

offset can be as large as ± 60 mV. Thus, single

ended measurements should be avoided. The

offset does not, however, affect differential

measurements.

40.2 to 90.2 Ω

RED

BLACK

WHITE

CLEAR

AG OR GND

GND

FIGURE 3-1. LI200X Schematic

LI200X PYRANOMETER

4. PROGRAMMING

Solar radiation can be reported as an average

flux density (W m-2) or daily total flux density

(MJ m-2). The appropriate multipliers are listed

in Table 4-1. Programming examples are given

for both average and daily total solar radiation.

The output from the LI200X is 0.2 kW m-2 mV-1.

4.1 AVERAGE SOLAR RADIATION

Example 1 shows the program instructions used

to measure the signal from the LI200X. A thirty

minute average is calculated and stored in final

storage.

TABLE 4-1. Multipliers Required for Average

Flux and Total Flux Density in Sl and

English Units

UNITS MULTIPLIER PROCESS

W m-2 200 Average

MJ m-2 t * 0.0002 Total

kJ m-2 t * 0.2 Total

cal cm-2 min-1 0.2 * (1.4333) Average

cal cm-2 t * 0.2 * (0.02389) Total

t = datalogger execution interval in seconds

EXAMPLE 1. Sample Instructions used to Measure an Average Flux with a CR10(X)/21X

;{CR10X}

;

*Table 1 Program

01: 10 Execution Interval (seconds)

01: Volt (Diff) (P2)

1: 1 Reps

2: 22** ± 7.5 mV 60 Hz Rejection Range

3: 1* DIFF Channel

4: 1* Loc [ W_m2 ]

5: 200*** Mult

6: 0 Offset

;Set negative values to zero.

;

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

1: 1* X Loc [ W_m2 ]

2: 4 <

3: 0 F

4: 30 Then Do

03: Z=F (P30)

1: 0 F

2: 0 Exponent of 10

3: 1* Z Loc [ W_m2 ]

04: End (P95)

05: If time is (P92)

1: 0 Minutes (Seconds --) into a

2: 30 Interval (same units as above)

3: 10 Set Output Flag High (Flag 0)

06: Real Time (P77)

1: 0110 Day,Hour/Minute

LI200X PYRANOMETER

07: Average (P71)

1: 1 Reps

2: 1* Loc [ W_m2 ]

-Input Locations-

1 W_m2

*Proper entries will vary with program and input channel assignments.

** The 15 mV slow range is used with a 21X.

*** See Table 4-1 for alternative multipliers.

4.2 TOTAL SOLAR RADIATION

In Example 2 a daily total flux density is found.

This total flux density is in MJ m-2 day-1.

Negative values are set to zero before they are

added to the running total.

4.2.1 Output Format Considerations

If the solar radiation is totalized in units of kJ

m-2, there is a possibility of overranging the

output limits. The largest number that the

datalogger can output to final storage is 6999

in low resolution and 99999 in high resolution

(Instruction 78, Set Resolution).

Assume that the daily total flux density is

desired in kJ m-2. Assume an irradiance of 0.5

kW m-2, the maximum low resolution output limit

will be exceeded in just under four hours. This

value was found by taking the maximum flux

density the datalogger can record in low

resolution and dividing by the total hourly flux

density.

()()

39 6999

0 5 3600

21 1

hr kJ m

kJ m s s hr

−

−− − (1)

To circumvent this limitation, record an average

flux (see Example 1). Then, during post

processing, multiply the average flux by the

number of seconds in the output interval to

arrive at a output interval flux density. Sum the

output interval totals over a day to find a daily

total flux density.

Another alternative is to record total flux using

the high resolution format (Instruction 78, see

Datalogger manuals for details). The

disadvantage of the high resolution format is

that it requires four bytes of memory per data

point, consuming twice as much memory as low

resolution.

LI200X PYRANOMETER

EXAMPLE 2. Sample Instructions used to Measure a Daily Total Flux Density with a CR10(X)/21X

;{CR10X}

;

*Table 1 Program

01: 10 Execution Interval (seconds)

01: Volt (Diff) (P2)

1: 1 Reps

2: 22** ± 7.5 mV 60 Hz Rejection Range

3: 1* DIFF Channel

4: 1* Loc [ MJ_m2 ]

5: .002*** Mult

6: 0 Offset

;Set negative values to zero.

;

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

1: 1* X Loc [ MJ_m2 ]

2: 4 <

3: 0 F

4: 30 Then Do

03: Z=F (P30)

1: 0 F

2: 0 Exponent of 10

3: 1* Z Loc [ MJ_m2 ]

04: End (P95)

05: If time is (P92)

1: 0 Minutes (Seconds --) into a

2: 1440 Interval (same units as above)

3: 10 Set Output Flag High (Flag 0)

06: Real Time (P77)

1: 0110 Day,Hour/Minute

07: Totalize (P72)

1: 1 Reps

2: 1* Loc [ MJ_m2 ]

-Input Locations-

1 MJ_m2

*Proper entries will vary with program and input channel assignments.

** The 15 mV slow range is used with a 21X.

*** See Table 4-1 for alternative multipliers.

LI200X PYRANOMETER

5. MAINTENANCE

On a monthly basis the level of the pyranometer

should be checked. Any dust or debris on the

sensor head should be removed. The debris

can be removed with a blast of compressed air

or with a soft bristle, camel hair brush. Check

that the drain hole next to the surface of the

sensor is free of debris.

CAUTION: Handle the sensor carefully

when cleaning. Be careful not to scratch

the surface of the sensor.

Recalibrate the LI200X every two years. Obtain

an RMA number before returning the LI200X to

Campbell Scientific, Inc. for recalibration.

6. CALIBRATION

LI200X pyranometers output a current that is

proportional to the incoming solar radiation.

Each LI200X has a unique calibration factor. A

variable shunt resistor in the cable converts the

current to the voltage measured by the

datalogger. Campbell Scientific sets the shunt

resistor so that the pyranometer outputs 5 mV

kW-1 m2.

The resistor value is found using Ohms law.

The resistance is found by dividing the desired

output voltage by the calibrated current output.

For example, a pyranometer with a calibration

of 92 µA kW-1 m2, will have the resistor set to:

54.35 Ω= −−

5 0 092

12 12

mV kW m mA kW m..

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