General Information
10 | CPW22
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SIL
Safety Integrity Level: Discrete level for specifying the safety integrity requirements of the safety functions, where
safety integrity level 4 has the highest level of safety integrity and safety integrity level 1 has the lowest.
[IEC 61508:2010]
PFD
Probability of Dangerous Failure Demand: Safety unavailability of safety-related system to perform the specified
safety function when a demand occurs from the control system.
[IEC 61508:2010]
SFF
Safe Failure Fraction: Property of a safety related element that is defined by the ratio of the average failure rates
of safe plus dangerous detected failures and safe plus dangerous failures.
[IEC 61508:2010]
SIL CL
SIL Claim Limit: Maximum SIL that can be claimed for a safety related electrical control system in relation to
architectural constraints and systematic safety integrity.
[IEC 62061:2005]
PFHd
Probability of dangerous Failure per Hour: Average probability of dangerous failure within 1 h.
[IEC 62061:2005]
MTTFd
Mean Time To dangerous Failure: Expectation of the mean time to failure. Normally expressed as an average of
expectation of the time to failure.
[EN ISO 13849-1:2015 and IEC 62061:2005]
OSSD
Output Signal Switching Device: Output switching element, verified by inspections or tests, independently and
continuously, able to detect the following foreseeable faults when in ON-state:
Short circuit of the output to supply voltage.
Short circuit of the output to ground.
Short circuit between outputs.
Overload.
[IEC 61496-1:2012]
SELV / PELV
Safety Extra-Low Voltage / Protective Extra-Low Voltage: Eletric system in wich the voltage cannot exceed the value
of extra-low voltage, protecting against eletric shock under normal operation and under single fault conditions,
including earth faults in order electric circuits.
[IEC 61140:2016]
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