Rockwell Automation Publication 1756-UM013B-EN-P - October 2019 131
Safety Data for Safety Modules Appendix D
1756-OBV8S Safety Data
Tab le 9 lists the safety data for the 1756-OBV8S module.
Table 9 - 1756-OBV8S Module Safety Data
Attribute
Output Mode
Sourcing Bipolar
Point Operation Type Point Operation Type
Single Dual Single
Safety Function Architecture (HFT) 0 1 1
Safe Failure Rate (λ
s
) [failures/hr] 1.16E-06 9.3E-07 9.5E-07
Safe Detected Failure Rate (λ
SD
)
(1)
1.16E-06 9.3E-07 9.5E-07
Safe Undetected Failure Rate (λ
SU
)
(1)
4.23E-10 5E-10 4.9E-10
Dangerous Failure Rate (λ
D
) [failures/hr] 9.01E-07 5.9E-07 6.1E-07
Dangerous Detected Failure Rate (λ
DD
) [failures/hr] 9.01E-07 5.9E-07 6.1E-07
Dangerous Undetected Failure Rate (λ
DU
) [failures/hr] 3.29E-10 3.1E-10 3.1E-10
SRT [millisecond] 4.5
Automatic Diagnostic Test Interval (TD) [hr] 4
Useful Life [yr] 20
Systematic Capability (SC) 3
Safe Failure Fraction (SFF) [%] 99.98% 99.98% 99.98%
PFH 3.29E-10 3.1E-10 3.1E-10
PFD
AVE
10 yrs 1.44E-05 1.4E-05 1.4E-05
Mission Time™ 20 yrs 2.89E-05 2.8E-05 2.8E-05
Diagnostic Coverage Average (DC
AVE
) 99.96% 99.95% 99.95%
Spurious Trip Rate (STR) 3.99E-06 2.68E-06 2.79E-06
MTTF [years] 55.50 75.09 72.91
MTTF
D
[years] 126.69 194.80 186.19
(1) (λSD) and (λSU) are calculated with assumption of Diagnostic Coverage of Safe Failure is same as Diagnostic Coverage of Dangerous Failure
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