Siemens SIMATIC ET 200S Installation And Operating Manual page 182

Glossary
The actual response time is between the shortest and the longest response time. The
longest response time must always be anticipated.
For fail-safe digital inputs: The response time is the time between a signal change at the
digital input and safe loading of the -> safety message frame on the backplane bus.
For fail-safe digital outputs: The response time is the time between an incoming safety
message frame from the backplane bus and the signal change at the digital output.
Reversing Starter
A reversing starter is a -> motor starter that determines the rotational direction of a motor. It
comprises a circuit-breaker and two contactors.
Safe State
The basic principle of the safety concept in F-systems is the existence of a safe state for all
process variables. For the digital F-I/O, the safe state is, for example, the value "0".
Safety function
Safety function is a mechanism built into the -> F-CPU and -> F-I/O that allows them to be
used in -> S7 Distributed Safety or S7 F/FH systems.
In accordance with IEC 61508: a safety function is implemented by a safety system to
ensure that the system is kept in a safe state or brought into a safe state in the event of a
particular fault
Safety Integrity Level
Safety Integrity Level (SIL) in accordance with IEC 61508 and prEN 50129. The higher the
Safety Integrity Level the more rigid the measures for prevention of systematic faults and for
management of systematic faults and hardware failures.
Safety modules can be used in safety mode up to SIL3.
Safety message frame
In safety mode, data is transferred between the -> F-CPU and the -> F-I/O in a safety
message frame.
Safety Mode
Safety mode is the operating mode of the -> F-I/O that allows -> safety-related
communication by means of -> safety message frames.
ET 200S -> fail-safe modules are designed for operation only in safety mode.
Safety Program
The safety program is a safety-related user program.
Glossary-8
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04