C-THERM TCi, Operator'S Manual, Page: 99 / 138

TCi Operator Manual
93
The slope A is equal to:
TCR R A
 
0
(2)
Where: TCR = Temperature Coefficient of Resistivity, assumed to be constant over the
measured temperature range.
Notes:
1. The slope depends on sensor resistance in general, and on R
0
in particular. Therefore,
even if 2 sensors have the same TCR , their temperature calibration lines will still have
different slopes if their resistance at a given temperature is not the same.
2. The higher slope, the more sensitive the sensor is. In other words, higher TCR and
higher sensor resistance will provide higher sensitivity.
For platinum used in the sensor, the TCR is approximately 0.0037 ºC
-1
, or 0.37% for each ºC.
To calculate the surface temperature of the sensor from (1) we use:
A
R T R
T
0
) (


(3)
The resistance may be measured directly by the electronics (using very low current and short
time to avoid sensor heating), or calculated from the initial voltage,
V
0
, or from the applied power
P (if applied power is the same for all sensors).
I
V
R
0

(4)
P
V
R
2
0

(5)
Where R is the measured sensor resistance at the said temperature,
I
is the current and P is the
power.
Software calibration parameters: A; R
0
9.1.2 Basic multi-point effusivity calibration
The heat equation with a constant supply of heat per sec per volume G’ is given below:
'
2
2
G
x
T
t
T
c
p






 
(6)
Assume two semi-infinite media in contact with heat generated at the interface at a constant rate
per unit area per unit time. Further assume that one medium is represented by the effusivity
sensor, and the other medium is the tested material, and both are at the same temperature and in