Siemens SIMATIC S7-400H - Communication Via Redundant S7 Connections

Communication
14.5 Communication via S7 connections
S7-400H
240 System Manual, 03/2012, A5E00267695-11
14.5.2 Communication via redundant S7 connections
Availability
Availability can be enhanced by using a redundant plant bus and two separate CPs in a
standard system.
Redundant communication can also be operated with standard connections. For this two
separate S7 connections must be configured in the program in order to implement
connection redundancy. In the user program, both connections require the implementation of
monitoring functions in order to allow the detection of failures and to change over to the
standby connection.
The following figure shows such a configuration.
&38
D
&38
E
&3
D
&3
E
&3
E
&38D
&38D
&3D
&3D
&3E
&3E
&38E
%XV
%XV
)DXOWWROHUDQW
)DXOWWROHUDQW
6WDQGDUGV\VWHP
6WDQGDUGV\VWHP
%ORFNGLDJUDP
%XV
%XV
Figure 14-10 Example of redundancy with fault-tolerant systems and a redundant bus system with
redundant standard connections
Response to failure
Double errors in the fault-tolerant system (i.e. CPUa1 and CPa 2) or in the standard system
(CPb1 and CPb2), and single errors in the standard system (CPUb1) lead to a total failure of
communication between the systems involved (see previous figure).