Safety Manual
Operating Instructions, 06/2012, A5E03433511-05
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Glossary
Dangerous failure
Failure with the potential to bring the safety-instrumented system into a dangerous or non-
functional status
Fail-safe
The capability of a control to maintain the safe state of the controlled device, e.g. machine,
process, or to bring the device to a safe state even when faults/failures occur.
Failure/Fault
Failure:
A resource is no longer capable of executing a required function.
Fault:
Undesired state of a resource indicated by the incapability of executing a required function.
Fault tolerance
Fault tolerance n means that a device can execute the intended task even when n faults
exist. The device fails to execute the intended function in case of n+1 faults.
Final controlling element
Converter that converts electrical signals into mechanical or other non-electrical variables.
Low Demand Mode
The frequency of demands for operation made on a safety-related system is not more than
one per year and not more than twice the proof-test frequency.
Risk
The combination of the probability of a damage occurring and its magnitude.
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