Siemens PM-E F pm DC24V PROFIsafe Installation And Operating Manual page 212

Glossary
Fail-safe modules
These are ET 200S modules that can be used for safety-related operation (-> safety mode)
in the ET 200S distributed I/O system. These modules are equipped with integrated -> safety
functions.
Fail-safe systems
Fail-safe systems (F-systems) remain in a safe state or immediately assume another safe
state as soon as particular failures occur.
Fault response time
The maximum fault response time of an F-system defines the interval between the
occurrence of any fault and a safe reaction at all affected fail-safe outputs.
For -> F-systems in general: The maximum fault response time defines the interval between
the occurrence of any fault at any -> F-I/O and the safe reaction at the corresponding fail-
safe output.
For digital inputs: The maximum fault response time defines the interval between the
occurrence of the fault and the safe reaction at the backplane bus.
For digital outputs: The maximum fault response time defines the interval between the
occurrence of the fault and the safe reaction at the digital output.
Fault tolerance time
The fault tolerance time of a process is the time a process can be left unattended without risk
to life and limb of the operating personnel, or damage to the environment.
Within the fault tolerance time, the F-system can initiate any process control actions, i.e. it
can control its process incorrectly or even not at all. The fault tolerance time depends on the
type of process and must be determined on a case-by-case basis.
F-CPU
An F-CPU is a central processing unit with fail-safe capability which is approved for use in
S7 Distributed Safety/S7 F/FH systems.
For S7 F/FH Systems, the F-copy license allows the central processing unit to be used as an
F-CPU. In other words, it can execute a -> safety program.
An F-copy license is not required for S7 Distributed Safety. The F-CPU can also execute a ->
standard user program.
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ET 200S Distributed I/O System - Fail-Safe Modules
Installation and Operating Manual, 08/2008, A5E00103686-07