User Manual

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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Principles of electrical design 2019-05-15
Measured value error of NTC sensors due to line resistance:
The sensors are highly non-linear. But thanks to the high sensor resistance the errors
are very small.
Error compared to T1:
NTC 100K
NTC10K
20°C
x 0.01
x 0.1
100°C
x 0.1
x 1 (~ equal)
Resistance transmitters (potentiometers):
2
0
-1 100 200 300
1 mm²
L [m]
4
6
8
F [Ohm]
10762d036
1,5 mm
²
2,5 mm²
0,6 mm Ø
Formula: F =
1
57
2
−
•
•
A
L
A Cable cross-section in mm
2
F Measurement error in ohms, due to line resistance (2RL for supply and
return conductor)
L Cable length in m
Explosion protection devices can falsify the measured value of analog inputs.
Example: Pepperl & Fuchs type CFD2-RR-Ex19 causes significant measuring errors for
resistance values of <30 ohms. Resistances >30 ohms are measured correctly.
Measured value error
NTC sensor
Measured value error
Resistance transmitters
a)
Measured value error
due to line resistance
Key
Measured value error
Resistance transmitters
b)
Measured value error
due to explosion
protection devices