Siemens SIMATIC ET 200AL System Manual page 133

ET-Connection
Backplane bus through which a connection is made. This allows bus participants to be
installed several meters from each other.
Fail-safe
Ability of a technical system to remain in a safe state or immediately switch to another safe
state when certain failures occur.
Fail-safe modules
ET 200AL modules with integrated safety functions that can be used for safety-related
operation (safety mode).
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 reaction time
The maximum fault reaction 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-system overall: The maximum fault reaction time defines the interval between the
occurrence of any fault in any → F-I/O and a safe response at the relevant fail-safe output.
For digital inputs: The maximum fault reaction time defines the interval between the
occurrence of the fault and the safe reaction on the backplane bus.
For digital outputs: The maximum fault reaction 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.
Any type of F-system control is tolerated within this fault tolerance time, i.e. the → F-system
can control its processes 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 that is permitted for use in
SIMATIC Safety. A standard user program can also be run on the F-CPU.
Distributed I/O system
System Manual, 08/2021, A5E31861578-AJ
Glossary
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