Glossary - Siemens SIMATIC S7-400H System Manual

Glossary

1-of-2 system
See Dual-channel H system
Comparison error
An error that may occur while memories are being compared on a fault-tolerant system.
Dual-channel H system
Fault-tolerant system with two central processing units.
Fail-safe systems
Fail-safe systems are characterized by the fact that, when certain failures occur, they remain
in a safe state or go directly to another safe state.
Fault-tolerant systems
Fault-tolerant systems are designed to reduce production downtime. Availability can be
enhanced, for example, by means of component redundancy.
H station
A fault-tolerant station containing two central processing units (master and standby).
H system
Fault-tolerant system consisting of at least two central processing units (master and standby).
The user program is processed identically in both the master and standby CPUs.
I/O, one-sided
We speak of a one-sided I/O when an input/output module can be accessed by only one of
the redundant central processing units. It may be single-channel or multi-channel (redundant).
I/O, redundant
We speak of a redundant I/O when there is more than one input/output module available for
a process signal. It may be connected as one-sided or switched. Terminology: "Redundant
one-sided I/O" or "Redundant switched I/O"
S7-400H
System Manual, 09/2007, A5E00267695-03
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