TCi Operator Manual
92
9 Theory of Operation
9.1
TCi Calibrations
9.1.1 Sensor temperature calibration
This section explains the relationship between the sensor’s change in temperature,
T
, its
resistance
R
and its voltage drop
V
, and how to calculate
T
from TCR (temperature
coefficient of resistivity) calibration parameters.
The TCR calibration is calibration of sensor resistance versus temperature, and is given in this
equation (assuming perfect linearity):
T
A
R
T
R
0
)
(
(1)
Where:
R(T)
= resistance of sensor at a given temperature (Ohm)
R
0
= resistance of sensor at 0ºC (Ohm)
T
= temperature (ºC)
A
= slope (Ohm/ºC)
Example of TCR calibration:
24C
y = 0.0872x + 23.257
R
2
= 0.9998
15C
y = 0.0836x + 22.162
R
2
= 0.9999
6C
y = 0.0859x + 23.006
R
2
= 0.9998
Slope=A
Intercept=R0
0
5
10
15
20
25
30
35
40
-100
-50
0
50
100
150
200
Temp. °C
R
e
s
is
ta
n
c
e
O
h
m
Sensor 24C
Sensor 6C
Sensor 15C
Linear (Sensor 24C)
Linear (Sensor 15C)
Linear (Sensor 6C)
Range of
A
~0.05 – 0.15 Ohm/ºC for this sensor design
Range of
R
0
~20 – 25 Ohm
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