Rockwell Automation Allen-Bradley 1715-IF16 User Manual

274 Rockwell Automation Publication 1715-UM001J-EN-P - December 2020
Appendix D PFD and PFH Calculations for a SIL 2 System
• PFDde = Probability of failure on demand for de-energize to action
systems
• PFDe = Probability of failure on demand for energize to action systems
• SFFde = Safe failure fraction for de-energize to action systems
• SFFe = Safe failure fraction for energize to action systems
• PFHde = Probability of failure per hour for de-energize to action systems
• PFHe = Probability of failure per hour for energize to action systems
PFD and PFH values in this manual are calculated with formulas explained in
IEC 61508, Part 6, Annex B. See IEC 61508, Part 6, for more information about
calculating PFD values for your system.
PFD Calculations with 24-hour MTTR
The PFD calculations in Table 60 are calculated for a 20-year mission time and
are specific to1715 I/O components in ControlLogix® systems.
Common Terms
λ = failure rate = 1/MTBF
λ
s
= rate of safe failures
λ
d
= rate of dangerous failures = (λ
du
+ λ
dd
)
λ
dd
= dangerous, detected failure rate = λ
d
x DC
λ
du
= dangerous, undetected failure rate = λ
d
x (1-DC)
SFF = safe failure fraction =(λ
s
+ λ
dd
)/(λ
s
+ λ
du
+λ
dd
)
T
CE1oo1
= channel equivalent down time = λ
du
/λ
d
x (T
1
/2 + MRT) + (λ
dd
/λ
d
x MTTR)
DC = diagnostic coverage
1oo2 Configuration (For energize to action: Dual 1715-OB8DE or 1715-OF8I)
STR
1oo2
= Spurious Trip Rate = 2 x (λ
s +
λ
dd
) + ß x (λ
s +
λ
dd
)
T
GE1oo2
= system equivalent down time = λ
du/
λ
d
x (T
1
/3 + MRT) + (λ
dd/
λ
d
x MTTR)
PFD
1oo2
= 2 x [(1-ß
D
) x λ
dd
+ (1-ß) x λ
du
]
2
x T
CE
x T
GE
+ (ß
D
x λ
dd
x MTTR) + ß x λ
du
x (T
1
/2 + MRT)
PFH
1oo2
= 2 x [(1-ß
D
) x λ
dd
+ (1-ß) x λ
du
] x (1-ß) x λ
du
x T
CE
+ ß x λ
du
2oo2 Configuration (For de-energize to trip: Dual 1715-OB8DE or 1715-OF8I)
STR
2oo2
= Spurious Trip Rate = 2 x (λ
s +
λ
dd
) x (λ
s +
λ
dd
) x MTTR + ß x (λ
s +
λ
dd
)
PFD
2oo2
= 2 x PFD
1oo1
PFH
2oo2
= 2 x PFH
1oo1
1oo2D Configuration (Dual configuration of 1715-AENTR, 1715-IB16D, or 1715-IF16)
STR
1oo2D
= Spurious Trip Rate = 2 x (λ
s +
λ
dd
) x (λ
s +
λ
dd
) x MTTR + ß x (λ
s +
λ
dd
)
T
CE
' = (λ
du
x (T1/2 + MRT) + ((λ
dd
+ λ
s
d
) x MTTR)) / (λ
du
+ λ
dd
+ λ
s
d
)
T
GE
' = T1/3 + MRT
PFD1oo2D = 2 x (1-ß) x λ
du
x ((1-ß) x λ
du
+ (1-ß
D
) x λ
dd
+ λ
s
d
) x T
CE
' x T
GE
' + 2 x (1 - K) x λ
dd
x T
CE
' + (ß x λ
du
x (T1/2 + MRT))
PFH
1oo2D = 2 x (1-ß) x λ
du
x ((1-ß) x λ
du
+ (1-ß
D
) x λ
dd
+ λ
s
d
) x T
CE
' + 2 x (1 - k) x λ
dd
+ ß x λ
du
Table 60 - PFD Calculations for 1715 I/O Components
Cat No.
Series
Firmware
Version
(1)
Description
Simplex Configuration Duplex Configuration
PFDde PFDe PFDde PFDe
1715-AENTR A 3.003 Ethernet adapter redundant module — — 1.26E-05 1.96E-05
1715-IB16D A 3.001 16-channel digital input module 6.44E-05 8.67E-05 8.37E-06 1.27E-05

Rockwell Automation Allen-Bradley 1715-IF16 Specifications

General

Brand	Rockwell Automation
Model	Allen-Bradley 1715-IF16
Category	I/O Systems
Language	English