Siemens SIMATIC S5 ET 200U - Simplified Illustration of a Configuration with Nonfloating I;O Modules

3-29
ET 200U Distributed I/O Station
EWA 4NEB 812 6087–02b
Nonfloating I/O modules work according to the following principle (see Fig-
ure 3-21):
S Input modules:
Reference potential is the M line (chassis ground of the control circuit). A
voltage drop on line  affects the input signal level V
I.
S Output modules:
Reference potential is terminal 2 (M) of the terminal block. A voltage drop
DV
2
on line  increases the chassis ground of the output driver and in this
way lowers the resulting control voltage V
ST
(see Figure 3-21).
For a nonfloating configuration, make sure that the voltage drop on lines 
and  never exceeds 1 V. Otherwise the reference potentials shift and the
modules can malfunction (see Figure 3-21).
ET 200U
interf. mod.
L+
+ 9 V
V
E
V
ST
M
D V
1
D V
2


12 12
24 V DC Supply
Data
GND
L+
M
Figure 3-21 Simplified Illustration of a Configuration with Nonfloating I/O Modules
Mechanical and Electrical Configuration