Siemens SIMATIC ET 200AL, System Manual

Page: 2106 / 2255

Connecting transducers
4.6 Wiring thermal resistors and resistors
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
75
3-wire connection of a thermal resistor
Depending on the module, for a 3-wire connection to modules with 4 terminals (per channel),
you may need to insert a bridge between M
0
- and I
C0
- (see figure below) or between M
0
+ and
I
C0
+. Always wire the I
C0
+ and M
0
+ lines directly to the thermal resistor. Use cable with wires
with identical cross-section.
For ET 200AL, ET 200eco PN and ET 200pro, no bridge is required as all necessary
connections are implemented internally.
Figure 4-8 Example: 3-wire connection of thermal resistor to an analog input module
2-wire connection of a thermal resistor
When installing a 2-wire device on modules with 4 terminals (per channel), you will need to
insert bridges at the module between M
0
+ and I
C0
+ and between M
0
- and I
C0
- as shown in the
figure below. The line resistance is measured, but not compensated. As a result of physical
limitations, this measurement type is less accurate than measurement with 3-wire or 4-wire
connections. The wiring for this type of measurement is, however, simple as the bridges
required can be wired in the plug, saving line.
For ET 200AL, ET 200eco PN and ET 200pro, no bridge is required as all necessary
connections are implemented internally.
Figure 4-9 Example: 2-wire connection of thermal resistor to an analog input module