Redundant Programmable Logic Controllers In The Simatic Series; Operating Objectives Of Redundant Programmable Logic Controllers - Siemens SIMATIC S7-400H Manual

Fault-Tolerant Programmable Logic Controllers
1.1 Redundant Programmable Logic Controllers in the
SIMATIC Series
Economic, and thus resource-sparing and low-pollution production can be achieved
nowadays in all branches of industry only by employing a high degree of
automation. At the same time there is a demand for fail-safe programmable logic
controllers with the greatest degree of distribution possible.
Redundant programmable logic controllers from Siemens have proved themselves
in operation and thousands are in service.
Perhaps you are already familiar with one of the fault-tolerant systems such as the
SIMATIC S5-115H and S5-155H, or the fail-safe S5-95F and S5-115F systems.
The S7-400H is the latest fault-tolerant PLC and we will be presenting it on the
pages that follow. It is a member of the SIMATIC S7 system family, meaning that
you can fully avail yourself of all the advantages of the SIMATIC S7.
Operating objectives of redundant PLCs
Redundant programmable logic controllers are used in practice with the aim of
achieving a higher degree of availability or fault tolerance.
Fault-tolerant 1-out-of-2 systems
Objective:
Reduce the probability of production
losses by switching to a standby sy-
stem
Figure 1-1
Note the difference between fault-tolerant systems and fail-safe systems. The
S7-400H is a fault-tolerant programmable logic controller that can be used only
with additional means for controlling processes relevant to safety.
1-2
Redundant automation systems, e.g

Operating objectives of redundant programmable logic controllers

Fail-safe 1-out-of-2 systems
Objective:
Protect life, the environment and
investments by safely disconnec-
ting to a secure "off" position
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07