Campbell EPPLEY PSP Manuel utilisateur

EPPLEY PSP

Precision Spectral Pyranometer

Instruction Manual

6/92

WARRANTY AND ASSISTANCE

The EPPLEY PSP -- Precision Spectral 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. 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 (403) 454-2505

FAX (403) 454-2655

Campbell Scientific Ltd.

Campbell Park

80 Hathern Road

Shepshed, Leics. LE12 9RP

ENGLAND

Phone (44)-50960-1141

FAX (44)-50960-1091

EPPLEY PSP

PRECISION SPRECTRAL PYRANOMETER

1. GENERAL

The EPPLEY Precision Spectral Pyranometer

(PSP) is a high quality pyranometer. It is

primarily used where high accuracy is required

or where it is used as a standard to calibrate

other pyranometers.

This manual provides information for interfacing

a CR10, 21X, and CR7 datalogger to a PSP.

An instruction manual provided by EPPLEY

contains the sensor calibration constant and

serial number. Cross check this serial number

against the serial number on your PSP to

ensure that the given calibration constant

corresponds to your sensor.

2. MEASUREMENT INSTRUCTION

The PSP (refer to Figure 1) outputs a low level

voltage ranging from 0 to a maximum of about

12mV depending on sensor calibration and

radiation level. 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) is a

possibility. As a test, wire the PSP as shown in

Figure 2 and make single-ended and differential

measurements. Compare results to determine

the acceptability of a single ended

measurement.

Figure 1. PSP Schematic

NOTE FOR 21X USERS: Slight ground

potential differences are created along the

21X analog terminal strip when the

datalogger power supply is powering

external peripherals. If the peripherals draw

30mA or greater, the PSP must be

measured differentially.

INPUT RANGE

An example showing how to determine the

optimum input range for a given sensor

calibration and maximum irradiance follows.

This is an example only. Your values will be

different.

EXAMPLE

-Sensor Calibration: Assume the sensor

calibration is 8.61 microvolts W-1 m2. This

is equivalant to 8.61 millivolts kW-1 m2.

-Maximum Irradiance: A reasonable

estimate of maximum irradiance at the

earth`s surface is 1 kW m-2.

-Input Range Selection: An estimate of the

maximum input voltage is obtained by

multiplying the calibration by the maximum

expected irradiance. That product is

8.61mV for this example. Select the

smallest input range which is greater than

the maximum expected input voltage. In this

case the 15mV range for the 21X and CR7,

and the 25mV range for the CR10 are

selected.

Measurement integration time is specified in the

input range parameter code. A more noise free

reading is obtained with the slow or 60 Hz

rejection integration. A fast integration takes

less power and allows for faster throughput.

MULTIPLIER

The multiplier converts the millivolt reading

to engineering units. Commonly used units

and how to calculate the multiplier are

shown in Table 1.

EPPLEY PSP

Table 1. Multipliers and Output Processing

OUTPUT/

UNITS MULTIPLIERS PRCSS

kJ m-2 (1/C)*t (Total)

kW m-2 (1/C) (Averages)

cal cm-2 (1/C)*t*(0.0239) (Total)

cal cm-2 min-1 (1/C)*(1.434) (Averages)

C= (EPPLEY calibration)

t= datalogger program execution

interval in seconds

3. OUTPUT FORMAT CONSIDERATIONS

The largest number that the datalogger can

output is 6999 in low resolution and 99999 in

high resolution (Instruction 78, set resolution). If

the measurement value is totalized, there is

some danger of overranging the output limits,

as shown in the following example.

EXAMPLE

Assume that daily total flux is desired, and the

datalogger scan rate is 1 second. With a

multiplier that converts the readings to units of

kJ m-2 and an average irradiance of .5 kW m-2,

the maximum low resolution output limit will be

exceeded in less than four hours.

Solution #1 - Record average flux density and

later multiply the result by the number of

seconds in the output interval to arrive at total

flux.

Solution #2 - Record total flux using the high

resolution format. The drawback to high

resolution is that it requires 4 bytes of memory

per data point, consuming twice as much

memory as low resolution.

4. CONNECTIONS

Differential and single-ended connections to the

datalogger are shown in Figures 2 and 3,

respectively.

*AG in Figure 2 refers to Analog Ground in the

CR10 which is the same as ground for the 21X

and CR7.

Figure 2. Differential Measurement

Connection

On a differential measurement, the low side of

the signal is jumpered to AG to keep the signal

in common mode range, as shown in Figure 2.

Figure 3. Single-ended Measurement

Connection

*AG in Figure 3 refers to Analog Ground in the

CR10, which is the same as ground for the 21X

and CR7.

5. RESOLUTION

The Eppley PSP outputs approximately 12mV

at 1400 watts meter-2 (solar constant). The

CR10 measures this sensor on the 25mV range

while the 21X and CR7 measure it on the 15mV

range.

An example of the datalogger resolution of the

PSP measurement with a PSP calibration of

8.61 mVw-1m2is given below:

CR10 differential resolution:

= ±0.00333mV * (1w/m2)/(.00861mV)

= ±0.387w/m2

EPPLEY PSP

CR10 single=ended resolution:

= ±0.00666mV * (1w/m2)/(.00861mV)

= ±0.773w/m2

21X differential resolution:

= ±0.001mV * (1w/m2)/(.00861mV)

= ±0.116w/m2

21X single-ended resolution:

= ±0.002mV * (1w/m2)/(.00861mV)

= ±0.232w/m2

6. SYSTEM ACCURACY

CR10 accuracy:

0.2% of Full Scale Range

= ±(0.002 * 25mV) * (1 wm-2/0.00861mV)

= 5.81w

21X accuracy:

0.1% of Full Scale Range

= ±(0.001 * 15mV) * (1 wm-2/0.00861mV)

= 1.74w

Eppley temperature dependance:

±1% over range from -20 to +40oC

Eppley linearity:

±.5% over range from 0 - 2800wm-2

Eppley cosine response:

±1% over range from 0 - 70o

±3% over range from 70-80o

System accuracy calculation example:

When solar radiation = 1117wm-2 at 10ofrom

normal (=1100wm-2 at 0o) and the temperature

is 25oC.

System accuracy = square root of the sum of

the squares of the random individual

component accuracies.

=±[(5.8w/m2)2+ (11w/m-2)2+ (5.5w/m-2)2

+(11w/m-2)2].5

=±17.5w/m-2 = ±1.6% of reading

Table des matières

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