Campbell Scientific CNR4 Net Radiometer - Manual (Page 22)

CNR4 Net Radiometer
For the pyrgeometer only
E = V/C + 5.67 •10 -8 •T 4 (7-2)
In this equation, C is the sensitivity of the sensor.
T is in Kelvin, and not in Celsius or Fahrenheit. NOTE
The downward-facing pyrgeometer measures the far infrared radiation that is
emitted by the ground. The upward-facing pyrgeometer measures the far
infrared radiation from the sky. As the sky is typically colder than the
instrument, one can expect negative voltage signals from the upward-facing
pyrgeometer. Equation 7-2 is used to calculate the far infrared irradiance of the
sky and of the ground.
7.1.3 Measuring CNR4 Temperature with Thermistor
The CNR4 has two temperature sensors built inside: thermistor and Pt-100;
both have identical accuracy. Using the thermistor is recommended when
using Campbell Scientific dataloggers. The thermistor has a greater resistance
(10 k
Ω @ 25°C) than Pt-100 sensor (100 Ω @ 0°C), and the change in
resistance with respect to temperature, in absolute terms, is greater. Therefore,
the cable resistance can be neglected, and the thermistor can easily be
measured using Half-Bridge Measurement instruction on Campbell Scientific
dataloggers.
TABLE 7-1 shows the thermistor resistance values as a function of
temperature.
TABLE 7-1. Resistance values versus CNR4’s thermistor temperature in °C.
Temperature
[ °C]
Resistance
[ Ω]
Temperature
[ °C]
Resistance
[ Ω]
Temperature
[ °C]
Resistance
[ Ω]
–30
–29
–28
–27
–26
–25
–24
–23
–22
–21
–20
–19
–18
–17
–16
–15
–14 135200
127900
121100
114600
108600
102900
97490
92430
87660
83160
78910
74910
71130
67570
64200
61020
58010
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
29490
28150
26890
25690
24550
23460
22430
21450
20520
19630
18790
17980
17220
16490
15790
15130
14500 30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46 8194
7880
7579
7291
7016
6752
6500
6258
6026
5805
5592
5389
5193
5006
4827
4655
4489
14