Campbell Scientific 110PV Surface Temperature Probe - Manual (Page 24)

110PV Surface Temperature Probe
6. Measurement
Understanding the details in this section is not necessary for general operation
of the 110PV Probe with CSI's dataloggers.
G
Ω
Signal
GREEN Sense +
Volt Excite
WHITE Sense -
Signal Reference
RED
BLACK
PURPLE
Signal Reference BLUE
THERMISTOR
CLEAR (shield)
4.99 k , 0.1%
FIGURE 6-1. 110PV Thermistor Probe schematic
Simple half bridge measurement, ignoring cable resistance
The measured voltage, V, is:
t
EX R
V V
+
=
990 , 4
990 , 4
Where V
EX
is the excitation voltage, 4,990 ohms is the resistance of the fixed
resistor and R
t
is the resistance of the thermistor
The resistance of the thermistor is:
⎟
⎠
⎞
⎜
⎝
⎛
− = 1 990 , 4
V
V
R EX
t
The Steinhart-Hart equation is used to calculate temperature from Resistance:
3
)) (ln( ) ln(
1
T T
K
R C R B A
T
+ +
=
Where T
K
is the temperature in Kelvin. The Steinhart- Hart coefficients used
are:
A = 1.129241x10 -3
B = 2.341077x10 -4
C = 8.775468x10 -8
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