Rockwell Automation 20A-DG01, Руководство пользователя

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Rockwell Automation Publication PFLEX-UM003D-EN-P - June 2021 9
General Description
The SIL value for a low demand safety-related system is directly related to
order-of-magnitude ranges of its average probability of failure to satisfactorily
perform its safety function on demand or, simply, average probability of failure on
demand (PFDavg). The SIL value for a High Demand/Continuous mode safety-related
system is directly related to the probability of a dangerous failure occurring per hour
(PFH).
PFDavg and PFH Data
These PFDavg and PFH calculations are based on the equations from Part 6 of
IEC 61508 and show worst-case values.
This table provides data for a 20-year proof test interval and demonstrates the
worst-case effect of various configuration changes on the data.
PowerFlex 40P
PFDavg and PFH for 20-year Proof Test Interval
PowerFlex 70
PFDavg and PFH for 20-year Proof Test Interval
Terminology
Attribute Test Result
PFDavg 1.74E-05
PFH 2.0E-10
SFF 81%
Attribute Test Result
PFDavg 3.4E-05
PFH 3.9E-10
SFF 81%
Abbreviation Full Term Definition
PFDavg Probability of
Failure on
Demand
The average probability of a system to fail to perform
its design function on demand.
PFH Probability of
Failure per Hour
The probability of a system to have a dangerous failure
occur per hour.
SFF Safe Failure
Fraction
The sum of safe failures plus the sum of dangerous
detected failures divided by the sum of all failures.