Terminology - Siemens SINUMERIK 840D sl Function Manual

Appendix
A.5 Terminology
A.5

Terminology

Actuator
Converter that converts electrical signals into mechanical or other non-electrical
quantities.
Category
Used in EN 954-1 to "Classify safety-relevant parts of control with reference to
their immunity to faults and their behavior when a fault condition exists as a result
of the structural arrangement of the parts/components and/or their reliability".
Channel
Element or group of elements that execute function(s) independently of one
another.
2-channel structure
This is a structure that is used to achieve fault tolerance.
For instance, a 2-channel protective door control can only be implemented if at
least two enable circuits are available and the main circuit is redundantly shut
down or a sensor (e.g. Emergency Stop switch) with two contacts is interrogated
and these are separately routed to the evaluation unit.
Note:
Fail-safe
The ability of a control system, also when faults occur (failure), to maintain a safe
condition of the controlled equipment (e.g. machine, process), or to bring the
equipment into a safe condition.
Failure/fault
Failure
A piece of equipment or device can no longer execute the demanded function.
Fault
Undesirable condition of a piece of equipment or a device, characterized by the
fact that it is unable to execute the demanded function.
Fault tolerance
Fault tolerance N means that a piece of equipment can still execute the required
task even if N faults are present. For N+1 faults, the equipment can no longer exe-
cute the required function.
Redundancy
Availability of more than the necessary equipment to execute the required tasks.
A-500
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 03.2006 Edition
"Failure" is an event and "fault" is a condition.
© Siemens AG, 2006. All rights reserved
03.06