INSTRUCTION MANUAL
LI200X Pyranometer
Revision: 2/97
Copyright (c) 1994-1997
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.
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CAMPBELL SCIENTIFIC, INC.
RMA#_____
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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
i
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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
-2
-1
Sensitivity: 0.2 kW m
mV
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
L
I
C
O
R
P
Y
R
R
E
A
T
N
E
M
O
P
Y
3
2
2
0
0
1
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 2-3. 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).
FIGURE 2-1. 015 Pyranometer Mounting Arm
FIGURE 2-2. 025 Crossarm Stand and
019ALU Crossarm
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.
RED
H
40.2 to 90.2 Ω
BLACK
L
GND
WHITE
CLEAR
AG OR GND
FIGURE 3-1. LI200X Schematic
2
LI200X PYRANOMETER
4. PROGRAMMING
Solar radiation can be reported as an average
flux density (W m
-2
(MJ m
). 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
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.
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
-2
) or daily total flux density
-2
mV-1.
TABLE 4-1. Multipliers Required for Average
Flux and Total Flux Density in Sl and
English Units
UNITS MULTIPLIER
-2
W m
MJ m
kJ m
cal cm
cal cm
-2
-2
-2
min
-2
-1
t * 0.0002 Total
t * 0.2 Total
0.2 * (1.4333) Average
t * 0.2 * (0.02389) Total
200 Average
PROCESS
t = datalogger execution interval in seconds
;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
3
LI200X PYRANOMETER
07: Average (P71)
1: 1 Reps
2: 1* Loc [ W_m2 ]
-Input Locations1 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
-2
m
, 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
kW m
, the maximum low resolution output limit
-2
. Assume an irradiance of 0.5
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.
2
39
..
hr
=
0 5 3600
()()
6999
21 1
−− −
kJ m s s hr
kJ m
−
(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.
4
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 Locations1 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.
5
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
-1 m2
kW
.
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
54.35 Ω=
-1 m2
, will have the resistor set to:
−−
5 0 092
mV kW m mA kW m. .
12 12
6
A.1 LI200S PYRANOMETER
LI200S pyranometers have a 100 ohm shunt
resistor built into the cable. They can be directly
measured by Campbell Scientific dataloggers.
The input range and multipliers vary from one
pyranometer to another. See Sections A.3 and
A.4 for calculating the proper input range and
multiplier.
A.1.1 WIRING
APPENDIX A
The red lead is connected to the high side (H)
of a differential input channel and the black lead
to the corresponding low side (L). On the CR10
a jumper wire is installed between the low side
and analog ground (AG). The clear lead is
connected to ground (G). On the 21X the
jumper wire is installed between the low side
and ground (G) and the clear lead is also
connected to ground (G). The measurement is
then made with Instruction 2 (see Section 4).
A.2. UNMODIFIED PYRANOMETERS
Pyranometers that do not have variable or fixed
shunt resistors built into the cable can still be
measured by Campbell Scientific dataloggers.
This is done by wiring in a 100 Ω shunt resistor
directly onto the datalogger wiring panel. The
input range and multipliers vary from one
pyranometer to another. See Sections A.3 and
A.4 for calculating the proper input range and
multiplier.
A.2.1 WIRING
Signal positive is connected into the high
side(H) of a differential input channel and signal
negative to the corresponding low side (L). A
jumper wire is installed between the low side (L)
and analog ground (AG) on the CR10 wiring
panel or ground on the 21X. A 100 Ω 1%
resistor (P/N 191) is installed on the wiring
panel between the high and low sides the
measurement channel. The measurement is
then made with Instruction 2 (see Section 5).
FIGURE A.2-1. Unmodified Pyranometer
Wiring Schematic
A.3. INPUT RANGE
The following is an example of how to
determine the optimum input range for a given
sensor calibration and maximum expected
irradiance. This is an example only. Your
values will be different.
This example uses the calibration provided by
LI-COR, Inc. Assume that the sensor calibration is
87 µA kW
which is converted to voltage by the 100 Ω shunt
resistor in the cable or on the wiring panel. To
convert the calibration from current to voltage,
multiply the LI-COR calibration by 0.1 KΩ (shunt
resistor). The example calibration changes to
8.7 mV kW
A reasonable estimate of maximum of
irradiance at the earth's surface is 1 kW m
Thus, an estimate of the maximum input
voltage is obtained by multiplying the calibration
by the maximum expected irradiance. In this
example that product is 8.7 mV. Now, select
the smallest input range which is greater than
the maximum expected input voltage. In this
case the 25 mV slow range for the CR10 and
15 mV slow range for the 21X are selected.
-1 m2
. The pyranometer outputs current
-1 m2
.
-2
.
A-1
APPENDIX A
A.4. MULTIPLIER
The multiplier converts the millivolt reading to
engineering units. The most common units and
equations to calculate the multiplier are listed in
Table A.4-1.
TABLE A.4-1. Multipliers Required for
Average Flux and Total Flux Density for SI
and English Units for a LI200S Pyranometer.
UNITS MULTIPLIER
-2
W m
MJ m
kJ m
cal cm
cal cm
-2
min
-2
-2
-1
-2
(1/C) * 1000 Average
t * (1/C) * 0.001 Total
t * (1/C) Total
(1/C) * (1.4333) Average
t *(1/C) * (0.02389) Total
C = (LI-COR calibration)
PROCESS
0.1
*
t = datalogger execution interval in seconds
A-2
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