Siemens SINUMERIK ONE NCU 1740 Equipment Manual page 135

Measurement using a 4-wire connection system
Notes regarding the connection and operation of PT100 resistors:
This enables the module to supply X3 with a constant current via the CO1, CI1, CO2 and CI2
terminals. The constant current is fed to the resistor to be measured where it is then measured
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 precision in comparison with 2-wire connections.
x
ADU
I
c
Figure 12-14
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.
NCU 1740
Equipment Manual, 09/2022, A5E51087503B AC
1, 2
Analog Digital Unit
Constant current
PT100 pin assignment
Connectable components
12.2 PP 72/48D PN and PP 72/48D 2/2A PN
135