I/O, Redundant; I/O, Single–Channel; I/O, Switched; Linking - Siemens SIMATIC S7-400H Manual

Glossary

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–way or switched.
Usage: "redundant one–way I/O" or "redundant switched I/O"
I/O, single–channel
We speak of a single–channel I/O when – in contrast to a redundant I/O – there
is only one input/output module for a process signal. It may be connected as
one–way or switched.

I/O, switched

We speak of a switched I/O when an input/output module can be accessed by all
of the redundant central processing units on a fault–tolerant system. It may be
single–channel or multi–channel (redundant).

Linking

In the link–up system mode of a fault–tolerant system the master CPU and the
standby CPU compare the memory configuration and the contents of the
loadmemory. If they establish differences in the user program, the master CPU
updates the user program of the standby CPU.
Master CPU
The central processing unit that is the first redundant central processing unit to
start up. It continues to operate as the master when the redundancy connection
is lost. The user program is processed identically in both the master and standby
CPUs.
Meantime between failures (MTBF)
The average time between two failures and, consequently, a criterion for the re-
liability of a module or a system.
Meantime down time (MDT)
The mean down timeMDT essentially consists of the time until error detection
and the time required to repair or replace defective modules.
Meantime to repair (MTTR)
"Meantime to repair" denotes the average repair time of a module or a system, in
other words, the time between the occurrence of an error and the time when the
error has been rectified.
Glossary-2
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07