Siemens PPU 26x.3 series Manual page 216

Connectable components
7.8 PP 72/48D PN and PP 72/48D 2/2A PN
as the voltage drop. It is imperative to wire the connected constant current cables directly to
the resistor.
Measurements with 4-wire connections compensate for line resistances and return a
considerably higher degree of measuring accuracy in comparison with 2-wire connections.
x
ADU Analog Digital Unit
I
c
Figure 7-54
Measurement using a 3-wire connection system
The following pins must be jumpered at connector X3 in order to perform the measurement in
the Pt100 using a 3-wire connection system:
● Temperature measurement with channel 1:
Short-circuit pin 2 (CI 1) and pin 4 (AI 1-) and connect the jumper at connector X3
● Temperature measurement with channel 2:
Short-circuit pin 6 (CI 2) and pin 8 (AI 2-) and connect the jumper at connector X3.
Note
Measuring accuracy
The accuracy of the temperature input becomes poorer: The resistance of the connecting
cable of the jumpered connecting cable falsifies the measurement.
216
1, 2
Constant current
Pt100 pin assignment
PPU and components
Manual, 10/2015, 6FC5397-2DP40-5BA3