Rockwell Automation Publication 1734-UM013C-EN-P - August 2010 135
Appendix
B
Probability of Failure on Demand (PFD),
Probability of Failure per Hour (PFH), and
Mean Time Between Failure (MTBF) Data
What This Appendix
Contains
This appendix lists calculated values for probability of failure on demand,
probability of failure per hour, and mean time between failure.
Calculated Values
See the table that shows the values. Reference information in the GuardLogix
Controller Systems Safety Reference Manual, publication 1756-RM093
.
Calculated values of probability of failure on demand and probability of failure
per hour appear in the table and must be calculated for the devices within the
system to comply with the SIL level required for application.
Users must be responsible for following the requirements of ISO 13849-1:2008,
to assess performance levels in their safety system.
Within the proof test interval, every I/O module must be functionally tested by
individually toggling each input point and verifying that it is detected by the
controller.
Additionally, each output point must be individually toggled by the controller
and user-verified that the output point changes state.
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