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S5-95F
5.8.2
Potential Bonding and Galvanic Isolation of External I/Os
The PLC is powered by its own control circuit. The I/Os are powered by the load circuit.
The circuits can be:
•
Connected to the same grounding point (non-floating); or
•
Galvanically isolated (floating)
Example of a Non-Floating Connection with Digital Modules
A 24-V DC load circuit has the same chassis grounding as the PLC's control circuit.
The common chassis grounding connection makes it possible for you to use reasonably priced non-
floating I/Os. These modules function according to the following principles.
•
Input modules:
•
Output modules:
Connection of Single-Channel Non-Floating External I/Os
L+
24 V DC supply
M
Figure 5-22. Simplified Representation of a Non-Floating, External I/O Connection
EWA 4NEB 812 6210-02
The M cable (control circuit chassis ground) is the reference potential.
A voltage drop on cable affects the input signal level V
Terminal 2 (M) of the terminal block is the reference potential. A voltage
drop V
on cable
raises the chassis ground of the output driver and
2
thereby reduces the resulting control voltage V
S5-95F
basic unit
L+
M
Expansion of Basic System with External I/Os
V
I
V
1
V
2
.
I
.
CV
+9 V
Data
GND
V
CV
1
2
5-25
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