Siemens SIMATIC PCS 7 Function Manual page 18

Basics of Fault Tolerance
2.3 PCS 7 redundancy concept
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Illustration of fault tolerance using redundancy nodes
Redundancy nodes can be used to provide an overview of the fault tolerance of a process
control system. As an introductory example, the following illustration presents the process
control system shown above as a block diagram with the individual redundancy nodes.
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Description
Several clients (OS clients, BATCH clients, Route Control clients) can access data on a
server (OS server, BATCH server, Route Control server).
Communication between the operator stations (client and server) and communication with
the engineering station is over a redundant, fault-tolerant terminal bus (Industrial Ethernet).
The clients and server are connected to the terminal bus via switches.
The servers (OS server, BATCH server, Route Control server, maintenance server, central
archive server) can, when necessary, be set up redundantly.
Automation systems communicate with the OS servers/Route Control servers and
engineering stations and among themselves over the redundant, fault-tolerant plant bus
(Industrial Ethernet).
The automation systems, server and engineering station are connected to the plant bus via
switches.
Each part of the redundant, fault-tolerant S7-400H automation systems is connected to the
plant bus with an Ethernet communications processor (CP).
Each part of the AS be connected to several PROFIBUS DP chains. The internal PROFIBUS
DP interfaces or additional communications processors are used for the attachment.
The redundant connection to the DP master system is achieved using two 153-2 IM modules
in each ET 200M.
Equivalent connection via PROFINET - You can find information about this in the section
"Fault-tolerant fieldbus based on PROFINET (Page 64)"
Using redundant digital or analog input/output modules, you can evaluate signals from
sensors/actuators. If one of the two redundant modules fails, the input/output signal of the
functioning module are evaluated.
Fieldbus systems can be connected to the redundant PROFIBUS DP.
The configuration of a redundant fieldbus can be realized with a redundant gateway (for
example, PA link). The field devices are connected to the subsystem (for example,
PROFIBUS PA) via AFD, active field distributors, (or AFS when ring/coupler redundancy is
used).
The Y Link allows you to connect non-redundant PROFIBUS distributed I/O devices to a
redundant PROFIBUS DP.
Fault-tolerant Process Control Systems (V8.0)
Function Manual, 03/2012, A5E02779471-02