362 The Safe torque off function
Safety data
The safety data for the Safe torque off function is given below.
Note: The safety data is calculated for redundant use, and does not apply if both STO
channels are not used.
• The following temperature profile is used in safety value calculations:
• 670 on/off cycles per year with T = 71.66 °C
• 1340 on/off cycles per year with T = 61.66 °C
• 30 on/off cycles per year with T = 10.0 °C
• 32 °C board temperature at 2.0% of time
• 60 °C board temperature at 1.5% of time
• 85 °C board temperature at 2.3% of time.
• The STO is a type B safety component as defined in IEC 61508-2.
• Relevant failure modes:
• The STO trips spuriously (safe failure)
• The STO does not activate when requested
A fault exclusion on the failure mode “short circuit on printed circuit board” has been
made (EN 13849-2, table D.5). The analysis is based on an assumption that one
failure occurs at one time. No accumulated failures have been analyzed.
• STO reaction time (shortest detectable break): 1 ms
• STO response time: 2 ms (typical), 25 ms (maximum)
• Fault detection time: Channels in different states for longer than 200 ms
• Fault reaction time: Fault detection time + 10 ms
• STO fault indication (parameter 31.22) delay: < 500 ms
• STO warning indication (parameter 31.22) delay: < 1000 ms
Frame size
SIL/
SILCL
PL
SFF
PFH
(T
1
= 20 a)
PFD
avg
(T
1
= 2 a)
PFD
avg
(T
1
= 5 a)
MTTF
D
DC
Cat. SC HFT CCF
T
M
(%) (1/h) (a) (%) (a)
2×R8i 3 e >99 6.2E-11 5.5E-07 1.3E-06 16330
>
90 3 3 1 80 20
3×R8i 3 e >99 7.3E-11 6.5E-07 1.6E-06 12390
>
90 3 3 1 80 20
4×R8i 3 e >99 8.4E-11 7.6E-07 1.9E-06 9980
>
90 3 3 1 80 20
3AXD10000078136 D
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