li200s pyranometer - Campbell Scientific

LI200S PYRANOMETER
REVISION: 2/96
COPYRIGHT (c) 1981-1996 CAMPBELL SCIENTIFIC, INC.
WARRANTY AND ASSISTANCE
The LI200S LI-COR PYRANOMETER is warranted by CAMPBELL SCIENTIFIC
(CANADA) CORP. (“CSC”) 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. CSC's obligation under this warranty is limited to repairing or replacing (at
CSC's option) defective products. The customer shall assume all costs of removing,
reinstalling, and shipping defective products to CSC. CSC will return such products by
surface carrier prepaid. This warranty shall not apply to any CSC 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. CSC is not liable for
special, indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. To obtain a Return
Merchandise Authorization (RMA), contact CAMPBELL SCIENTIFIC (CANADA)
CORP., at (780) 454-2505. An RMA number will be issued in order to facilitate Repair
Personnel in identifying an instrument upon arrival. Please write this number clearly on
the outside of the shipping container. Include description of symptoms and all pertinent
details.
CAMPBELL SCIENTIFIC (CANADA) CORP. does not accept collect calls.
Non-warranty products returned for repair should be accompanied by a purchase order
to cover repair costs.
LI200S PYRANOMETER
1. GENERAL
This manual provides information for
interfacing a CR10, 21X, and CR7 datalogger
to a LI200S Pyranometer. An instruction
manual provided by LI-COR contains the
sensor calibration constant and serial number.
Cross check this serial number against the
serial number on your LI200S to ensure that
the given calibration constant corresponds to
your sensor.
2. SPECIFICATIONS
Stability:
<±2% change over a 1
year period
Response Time:
10 µs
Temperature
Dependence:
0.15% per °C maximum
Cosine Correction: Cosine corrected up to 80°
angle of incidence
Operating
Temperature:
-40 to 65°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 x
2.54 cm);
Weight:
1 oz. (28 g)
Accuracy:
Absolute error in natural
daylight is ±5% maximum;
±3% typical
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.
3. MEASUREMENT INSTRUCTION
The LI200S (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 singleended measurement (Instruction 1) is a
possibility. As a test, wire the LI200S as shown
in Figure 2 and make single-ended and
differential measurements. Compare results to
determine the acceptability of a single ended
measurement.
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 about 30mA or greater,
the LI200S must be measured differentially.
Typical Sensitivity: 0.2 kWm-2mV-1
Linearity:
Maximum deviation of 1%
up to 3000 Wm-2
Shunt Resistor:
Adjustable, 40.2 to 100 Ω,
factory set to give the
above sensitivity
Light Spectrum
Waveband:
400 to 1100 nm
Figure 1. LI200S Schematic
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.
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LI200S PYRANOMETER
EXAMPLE
EXAMPLE
-Sensor Calibration: Assume the sensor
calibration is 87 microamps kW -1 m-2. The
LI200S outputs amperage which is converted to
voltage by 100 ohm shunt resistor in the cable,
as shown in Figure 1. To convert the
calibration from microamps to millivolts,
multiply the calibration by 0.100. The example
calibration changes to 8.7 mV kW -1 m-2.
-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.
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.
5. CONNECTIONS
Differential and single-ended connections to
the datalogger are shown in Figures 2 and 3,
respectively.
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.
Table 1. Multipliers Required for Flux
Density and Total Fluxes
kJ m-2
kW m-2
cal cm-2
cal cm-2 min-1
(1/C)t
(1/C)
(1/C)t(0.0239)
(1/C)(1.434)
(Total)
(Average)
(Total)
(Average)
Figure 2. Differential Measurement
Connection
*AG in Figure 2 refers to Analog Ground in the
CR10 which is the same as ground for the 21X and
CR7.
On a differential measurement, jumper the low
side of the signal to AG to keep the signal in
common mode range, as shown in Figure 2.
C = (LI-COR calibration)*0.100
t = datalogger program execution
interval in seconds
4. 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.
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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.
LI200S PYRANOMETER
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