Siemens SIMATIC S5-100U System Manual page 64

Installation Guidelines
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 ground line, line M (control circuit chassis) is the reference potential. A voltage drop V
on line affects the input signal level V
• Output modules
- Terminal 2 (M) of the terminal block is the reference potential. A voltage drop V
line raises the chassis potential of the output driver and thus reduces the resulting control
voltage V .
CV
Figure 3-22 shows a simplified connection of the S5-100U with a non-floating external I/O.
L+
24 V DC supply
M
Figure 3-22. Simplified Representation of a Non-Floating I/O Connection
3-26
.
I
CPU
L+
M
V
1
V
2
V
I
1
EWA 4NEB 812 6120-02b
S5-100U
1
on the
2
+9 V
Data
GND
V
CV
2