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
Overvoltage protection devices can falsify the measured value of analog inputs.
Example: Phoenix type PT 1X2-12DC-ST/28 56 02 9 has an internal protective impe-
dance which causes a measuring error of +1K, but only for LG-Ni 1000 sensors.
Pt 1000 Ω sensors: Measured value error due to line resistance
2
1
0
100 200 300
1 mm
²
F [K]
L [m]
1,5 mm
²
2,5 mm
²
10762d035
0,6 mm Ø
-0,26
Formula: F =
3.9
1
A57
L2
−
•
•
Key
A Cable cross-section in mm
2
F Measured temperature error in K
L Cable length in m
• The 4-wire circuit serves to eliminate the error due to line resistance.
The measuring value function has no predefined line resistance.
• in addition, the very small pulsed sensor current minimizes the internal heat
dissipation in the Pt100 sensor.
T1 sensors: Measured value error due to line resistance:
0.2
0
-0.1 100 200
300
1 mm
²
L [m]
0.4
0.6
0.8
F [K]
10762d055
1,5 mm
²
2,5 mm
²
0,6 mm Ø
1.0
Formula: F =
10
1
A57
L2
−
•
•
A Cable cross-section in mm
2
F Measured temperature error in K
L Cable length in m
Measured value error
LG-Ni 1000
b)
Measured value error
due to explosion
protection devices
Measured value error
Pt 1000 sensor
Measured value
error
Pt 100
sensor
(4-wire)
Measured value er
ror
T1
Key