Basics Of Fault Tolerance; Rationale For Using Fault-Tolerant Process Control Systems - Siemens SIMATIC PCS 7 Function Manual

Basics of Fault Tolerance

2.1

Rationale for using fault-tolerant process control systems

Advantages of fault-tolerant components
Process control systems are responsible for controlling, monitoring and documenting
production and manufacturing processes. Due to the increasing degree of automation and the
demand for improved efficiency, the availability of these systems is playing an increasingly
important role.
Failure of the control system or any of its components can lead to costly downtime in production
and manufacturing. The expense involved in restarting a continuous process also has to be
taken into consideration along with the actual production losses resulting from a failure. In
addition, the loss of an entire batch may occur due to lost quality data. If the process is intended
to operate without supervisory or service personnel, a process control system must be
configured fault-tolerant for all of the components.
You can minimize the risk of a production failure and other detrimental effects by using fault-
tolerant components in a process control system. A redundant design ensures increased
availability of a control system. This means that all components involved in the process have
a backup in continuous operation that simultaneously participates in the control tasks. When
a fault occurs or one of the control system components fails, the correctly operating redundant
component takes over the continuing control task. The ultimate goal is to increase the fault
tolerance and fail-safe performance in process control systems.
The following applies to you as the plant operator:
The higher the cost of a production stoppage, the more you need a fault-tolerant system. The
higher initial investment usually associated with a fault-tolerant system is soon offset by the
savings resulting from decreased production downtimes.
Fault-tolerant PCS 7 process control system
The following components of the PCS 7 process control system allow you to implement fault-
tolerance at all automation levels in the form and to the degree you require:
● Operator stations, maintenance station, central archive server, BATCH stations, Route
Control stations (management level)
● Bus system
● Automation systems (process level)
● Distributed I/O (field level)
The following figure shows an example of a fault-tolerant process control system with PCS 7
components.
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA
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