A.4 Terms - Siemens Sinumerik 840D sl Function Manual

10/15
A.4 Terms
Actuator
Converter that converts electrical signals into mechanical or other non--electrical
quantities.
Category
Used in ISO 13849--1 to "Classify safety--related 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 an-
other.
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.
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.
Error
Undesirable condition of a piece of equipment or a device, characterized by the
fact that it is unable to execute the demanded function.
Note:
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 ex-
ecute the required function.
Performance Level (PL)
This is a measure defined in ISO 13849--1 for the safety--related performance of a
control system.
Redundancy
Availability of more than the necessary equipment to execute the required tasks.
© Siemens AG 2015 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
"Failure" is an event and "fault" is a condition.
Appendix

A.4 Terms

A-823