240 Rockwell Automation Publication 520-UM001K-EN-E - August 2021
Appendix G Safe Torque Off Function
• programming the application software and the safety option
configurations in accordance with the information in this manual.
• access control to the system, including access code handling.
• analyzing all configuration settings and choosing the proper setting to
achieve the required safety rating.
Functional Proof Test
The PFD and PFH values provided in the table below are contingent upon the
Proof Test Interval (PTI). Before the end of the PTI specified in the table below,
a proof test of the STO safety function must be performed in order for the
specified PFD and PFH values to remain valid.
PFD and PFH Data
PFD and PFH calculations are based on the equations from Part 6 of EN 61508.
This table provides data for a 20-year proof test interval and demonstrates the
worst-case effect of various configuration changes on the data.
Safety Reaction Time
The safety reaction time is the amount of time from a safety-related event as
input to the system until the system is in the Safe State.
The safety reaction time from an input signal condition that triggers a safe
stop, to the initiation of safe-torque-off, is 100 ms (maximum).
IMPORTANT When applying Functional Safety, restrict access to qualified, authorized personnel who
are trained and experienced.
ATTENTION: When designing your system, consider how personnel will exit the
machine if the door locks while they are in the machine. Additional safeguarding
devices may be required for your specific application.
PFD and PFH for 20-year Proof Test Interval
Attribute Value
PFD 6.62E-05 (MTTF = 3593 years)
PFH
D
8.13E-10
SFF 83%
DC 62.5%
CAT 3
HFT 1 (1oo2)
PTI 20 YEARS
Hardware
Type
Type A
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