Campbell Scientific CNR4 Net Radiometer - Manual (Page 39)

CNR4 Net Radiometer
voltmeter to its most sensitive range setting. Darken the sensor. The signal
n take up to one minute. Small deviations
al effects, such as touching
ct can be demonstrated by
the zero offset is
within specifications, proceed with the third test.
uld be exposed to light. The signal should be a
et the voltmeter range in such a way that the expected full-
ter is within the full-scale input range of the
voltmeter. The range can be estimated on theoretical considerations. When the
W/m 2 , which is roughly equal to normal
, and the sensitivity of the pyranometer is 15 μV per
xpected output range of the pyranometer is equal to 22500 μV, or
eter outp easured by (for ample, 22.5 mV by
sor sensitivity (15 μV/W/m 2 ). If no faults are found up to this point,
pyranometer is probably operating correctly.
8.2 Testing the Pyrgeometer
It is assumed that the zero offset is no more than a few watts per square meter
t in Section 8.1, Testing the Pyranometer).
ltage if
l to the temperature difference (see
tion).
The
pyrg
tput by the sensor’s sensitivity value, and subsequently
correcting for the temperature, according to Equation 5-2. If there are still no
lt
8.3 Testing th
Usin between the black and white wires
h
TAB
resist
Pt-1
e checked as well for reference.
value with the resistance values listed in TABLE 7–2.
The resistance should be above 100 Ω at 0°C, and the cable resistance should
should read zero; this response ca
from zero are possible; this is caused by the therm
the pyranometer with your hand. This thermal effe
deliberately heating the pyranometer with your hand. If
In the third test, the sensor sho
positive reading. S
scale output of the pyranome
maximum expected radiation is 1500
outdoor daylight conditions
W/m
2 , the e
22.5 mV. One can calculate the radiation intensity by dividing the
pyra
ut as m the voltmeter ex ) nom
n the se
your
(see second tes
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 vo
the hand is colder. The signal is proportiona
the rule of thumb in Section 7.1.6, Calculation of Net Long-wave Radia
radiation emitted by the hand can be calculated by dividing the
eometer ou
fau s found, your pyrgeometer is probably operating correctly.
e Thermistor
g a multimeter, measure the resistance
of t e thermistor, and compare the value with the resistance values listed in
LE 7-1. The resistance should be around 10 k Ω at 25 °C, and the cable
ance should add about 0.026 Ω per each foot of cable. When in doubt, the
00 resistance (temperature) can b
8.4 Testing the Pt-100
Using a multimeter, measure the resistance between the two opposite wires of
the Pt-100 (gray-yellow, gray-brown, green-yellow, green-brown), and
compare the measured
add about 0.026 Ω per each foot of cable. When in doub,t the thermistor
resistance (temperature) can be checked as well for reference.
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