S5-95F Expansion of Basic System with External I/Os
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: The M cable (control circuit chassis ground) is the reference potential.
A voltage drop on cable affects the input signal level V
I
.
• Output modules: Terminal 2 (M) of the terminal block is the reference potential.
A voltage
drop V
2
on cable raises the chassis ground of the output driver and
thereby reduces the resulting control voltage V
CV
.
Connection of Single-Channel Non-Floating External I/Os
Figure 5-22. Simplified Representation of a Non-Floating, External I/O Connection
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EWA 4NEB 812 6210-02
5-25
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