Rockwell Automation Publication 2198-UM001D-EN-P - May 2014 171
Kinetix 5500 Safe Torque-off - Integrated Safety Chapter 10
Probability of Dangerous
Failure Per Hour (PFH)
Safety-related systems are classified as operating in a High-demand/continuous
mode where the frequency of demands for operation made on a safety-related
system is greater than once per year.
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).
PFH Data
These PFH calculation is based on the equations from EN 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.
Determination of safety parameters is based on the assumption that the system
operates in high demand mode and that the safety function is requested at least
once a year.
This table provides data for a 20-year proof test interval.
Table 79 - PFH for 20-year Proof Test Interval
Determination of safety parameters is based on the assumption that the
system operates in High-demand mode and that the safety function is
requested at least once every three months.
Attribute Value
PFH (1e-9) 1.54
Proof test (years) 20
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