Campbell 110PV, Instruction Manual, Page: 21 / 38

110PV Surface Temperature Probe
13
The coefficients used for the Steinhart-Hart equation are:
A=1.129241*10
–3
B=2.341077*10 –4
C=8.775468*10 –8
8. Operation
8.1 Sensor Schematic
FIGURE 8-1. 110PV Thermistor Probe schematic
8.2 Measurement Details
Understanding the details in this section is not necessary for general operation
of the 110PV Probe with our dataloggers.
Simple half bridge measurement, ignoring cable resistance, has a measured
voltage, V, of:
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
+ +
=