
136
Rockwell Automation Publication 1734-UM013C-EN-P - August 2010
Appendix B
Probability of Failure on Demand (PFD), Probability of Failure per Hour (PFH), and Mean Time Between Failure (MTBF) Data
Figure 23 - Calculated Values for Probability of Failure on Demand (PFD),
Probability of Failure per Hour (PFH), and Mean Time Between Failure (MTBF)
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
1% of SIL 3 Limit
10% of SIL 3 Limit
PFD versus Proof Test Interval
Proof Test Interval (years)
PFD
Model
Proof Test Interval
(Mission Time)
PFD (1/hour)
PFH (1/hour)
MTBF (hour)
Year
Hour
1734-IB8S
1
8760
5.85E-07
1.34E-10
5.76E+06
2
17520
1.17E-06
5
43800
2.93E-06
10
87600
5.86E-06
20
175200
1.17E-05
1734-OB8S
1
8760
6.05E-07
1.38E-10
4.57E+06
2
17520
1.21E-06
5
43800
3.03E-06
10
87600
6.06E-06
20
175200
1.21E-05