Campbell CNR4, Руководство по эксплуатации продукта

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CNR4 Net Radiometer
22
from zero are possible; this is caused by the thermal effects, such as touching
the pyranometer with your hand. This thermal effect can be demonstrated by
deliberately heating the pyranometer with your hand. If the zero offset is within
specifications, proceed with the third test.
In the third test, the sensor should be exposed to light. The signal should be a
positive reading. Set the voltmeter range in such a way that the expected full-
scale output of the pyranometer is within the full-scale input range of the
voltmeter. The range can be estimated on theoretical considerations. When the
maximum expected radiation is 1500 W/m
2
, which is roughly equal to normal
outdoor daylight conditions, and the sensitivity of the pyranometer is 15 μ V per
W/m 2 , the expected output range of the pyranometer is equal to 22500 μ V, or
22.5 mV. One can calculate the radiation intensity by dividing the pyranometer
output as measured by the voltmeter (for example, 22.5 mV) by the sensor
sensitivity (15 μ V/W/m 2 ). If no faults are found up to this point, your
pyranometer is probably operating correctly.
9.1.2 Testing the Pyrgeometer
The zero offset is assumed to be no more than a few watts per square met re
(see second test in Section 9.1.1 , Testing the Pyranometer
(p. 21)
).
The CNR4 body and the ambient air should be at the same temperature. Let the
pyrgeometer rest for at least five minutes to regain its thermal equilibrium. Set
the voltmeter to its most sensitive range. To test if the pyrgeometer is working
properly, put your hand in front of the pyrgeometer. The thermal radiation from
your hand will cause the pyrgeometer to generate a positive voltage when the
surface temperature of your hand is higher than the pyrgeometer temperature.
The pyrgeometer will generate a negative voltage if the hand is colder. The
signal is proportional to the temperature difference (see the rule of thumb in
Section 8.6 ,
Calculation of Net Long-wave Radiation
(p. 20)
). The radiation
emitted by the hand can be calculated by dividing the pyrgeometer output by
the sensor sensitivity value, and subsequently correcting for the temperature,
according to Equation 8-2 . If there are still no faults found, your pyrgeometer
is probably operating correctly.
9.1.3 Testing the Thermistor
Use a multimeter to measure the resistance between the black and white wires
of the thermistor, and compare the value with the resistance values listed in
TABLE 8-1 . The resistance should be around 10 k Ω at 25 °C, and the cable
resistance should add about 0.026
Ω
per each foot of cable. When in doubt, the
Pt-100 resistance (temperature) can be checked as well for reference.
9.1.4 Testing the Pt-100
Use a multimeter to measure the resistance between the two opposite wires of
the Pt-100 (gr
e
y-yellow, gr
e
y-brown, green-yellow, green-brown), and
compare the measured value with the resistance values listed in TABLE 8–2 .
The resistance should be above 100 Ω at 0 °C, and the cable resistance should
add about 0.026
Ω
per each foot of cable. When in doubt, the thermistor
resistance (temperature) can be checked as well for reference.