System manual CECX / Temperature module CECX-E-6E-T-P2
CECX-II 24-10
24.6 Functional description
24.6.1 General functions for measuring temperatures with thermocouples
24.6.1.1 Principle of temperature measurements
θ
w
Cu
Cu
U
u
U
=(
θ
w
-
θ
u
).k
... [
V
K]
.
NiC
Ni
Temperature measurement
The thermocouple supplies (active) a voltage Uθ, which depends on the
temperature difference between the measuring point (w) and the compari-
son point (u, terminal). k is the temperature coefficient of the thermocouple.
It is dependent on the material and the temperature. Therefore a change in
the thermo-voltage is not proportional to the temperature change. The soft-
ware executes the linearization.
To enable evaluation of the temperature at the measuring point, the tem-
perature of the comparison point must be known. The latter is measured by
a terminal temperature sensor that is integrated into the module.
24.6.1.2 Temperature data sampling
TI0
+
-
U
f
GND_EXT0
Zähler
+
Logik
GND
Block diagram
The thermo voltage at the input terminals is amplified and converted into a
proportional frequency in the voltage-to-frequency converter. The meas-
urement period lasts 100 ms.
Due to the integrating measurement procedure used, any interference that
occurs at the AC line -frequency (50 Hz, 60 Hz) is filtered out.
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