Rs 485 Repeater In Ungrounded And Grounded Operation - Siemens SIMATIC S7-400 Reference Manual
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RS 485 repeater
10.4 RS 485 repeater in ungrounded and grounded operation
10.4
RS 485 repeater in ungrounded and grounded operation
Grounded or ungrounded
The following applies to the RS 485 repeater:
● It is grounded, if all other nodes on the segment are also operated on ground potential
● It is ungrounded, if all other nodes in the segment are operated with an ungrounded potential
Note
Bus segment 1 is grounded if you connect a programming device with a pure MPI interface
to the PG/OP socket of the RS 485 repeater. The segment is grounded, because the MPI
in the PG is grounded, and the PG/OP socket of the RS 485 repeater is connected internally
with bus segment 1. This does not apply when the programming device has a combination
MPI/DP interface.
Grounded operation of the RS 485 repeater
For grounded operation of the RS 485 repeater, you must jump terminals "M" and "PE" on the
top of the RS 485 repeater.
Ungrounded operation of the RS 485 repeater
For ungrounded operation of the RS 485 repeater, "M" and "PE" on the top of the RS 485
repeater must not be interconnected. In addition, the supply voltage to the RS 485 repeater
must be ungrounded.
Connection scheme
In a repeater configuration with ungrounded reference potential (ungrounded operation), any
interference currents and static charges are discharged to the protective conductor by means
of an RC network integrated in the repeater (refer to the figure below).
Figure 10-1
390
DC
L+ M PE M 5.2
24 V
A1 B1 A1 B1
1
RC network with 10 M Ohm for configuration with ungrounded reference potential
PE
22 nF
10 MΩ
M
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
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