Siemens SIMATIC S7-400H Manual page 203

Redundancy, functional
Redundancy with which the additional technical means are not only constantly in
operation but also involved in the scheduled function. Synonym: active
redundancy.
Redundant link
A link between the central processing units of a fault-tolerant system for
synchronization and the exchange of data.
Redundant mode
In the Redundant system mode of a fault-tolerant system the central processing
units are in RUN mode and are synchronized over the redundant link.
Redundant systems
Redundant systems are characterized by the fact that important automation
system components are available more than once (redundant). When a
redundant component fails, processing of the program is not interrupted.
Self-test
In the case of fault-tolerant CPUs defined self-tests are executed during startup,
cyclical processing and when comparison errors occur. These check the contents
and the state of the CPU and the I/Os.
Solo mode
In the Solo system mode of a fault-tolerant system the master CPU is in
RUN mode, whereas the standby CPU is at STOP, ERROR-SEARCH or
DEFECTIVE.
Standby CPU
The redundant central processing unit of a fault-tolerant system that is linked to
the master CPU. It goes to STOP when the redundant link is lost. The user
program is processed in an identical manner in both the master and standby
CPUs.
Stop
With fault-tolerant systems: in the Stop system mode of a fault-tolerant system
the central processing units of the fault-tolerant system are in STOP mode.
Synchronization submodule
An interface module to the redundant link on a fault-tolerant system.
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Glossary
Glossary-3