
Rockwell Automation Publication 1756-RM001I-EN-P - May 2012
115
PFD Calculations for a SIL 2 System
Appendix C
5-year PFD Calculations
The PFD calculations in
are calculated for a 5-year proof test interval
and are specific to ControlLogix system components.
1794-OF4IXT
(4)
FLEX I/O-XT 4 analog output module
5,493,902
1.8202E-07
—
1.4772E-07
1794-TB3
FLEX I/O terminal base unit
250,000,000
4E-09
—
1.47E-07
1794-TB3G
FLEX I/O generic terminal base unit
100,000,000
0.00000001
—
1.47024E-07
1794-TB3GS
FLEX I/O generic terminal base unit
100,000,000
0.00000001
—
1.47024E-07
1794-TB3S
FLEX I/O terminal base unit
100,000,000
0.00000001
—
1.47024E-07
1794-TB3T
FLEX I/O temperature terminal base unit
100,000,000
0.00000001
—
1.47024E-07
1794-TB3TS
FLEX I/O temperature terminal base unit
52,312,000
1.91161E-08
—
1.47061E-07
1794-TBN
FLEX I/O terminal base unit
100,000,000
0.00000001
—
1.47024E-07
1794-TBNF
FLEX I/O fused terminal base unit
100,000,000
0.00000001
—
1.47024E-07
(1) Refer to the Revision Release List available at
from the Product Certifications link.
(2) References a series A component if no other series is indicated by /
X
.
(3) The PFD calculations ControlLogix chassis are completed using an arithmetic average of the MTBFs for all five chassis types (that is chassis 1756-A4, 1756-A7, 1756-A10, 1756-A13,
and 1756-A17).
(4) Calculated values.
(5) Calculated values (615082-010).
(6) 1oo2 is required for compliance to edition 2 of IEC 61508.
(7) SIL 2-rated for non-interference in the chassis. However, I/O is not for use within a safety function.
(8) Calculations for the redundant power supply are completed with the presumption that both power supplies fail simultaneously.
(9) MTBF measured in hours. The values used here represent values available in January 2012.
(10)
λ
= Failure Rate = 1/MTBF.
Table 11 - PFD Calculations - 2-year for ControlLogix Component
Cat. No.
(1)
(2)
Description
61508
(2010)
Mean Time Between
Failure (MTBF)
(9)
λ
(10)
Calculated PFD
1oo1
Architecture
1oo2
Architecture
Table 12 - PFD Calculations - 5-year for ControlLogix Component
Cat. No.
(1)
(2)
Description
61508
(2010)
Mean Time Between
Failure (MTBF)
(9)
λ
(10)
Calculated PFD:
1oo1
Architecture
1oo2
Architecture
1756-A
XX
/B
(3)
ControlLogix chassis
22,652,009.8
4.415E-08
4.8362E-05
—
1756-A4LXT
ControlLogix-XT chassis
1,069,120
9.353E-07
1.0247E-03
—
1756-A5XT/B
ControlLogix-XT chassis
734,420
1.362E-06
1.4917E-03
—
1756-A7LXT
ControlLogix-XT chassis
27,628,178
3.619E-08
3.9652E-05
—
1756-A7XT/B
ControlLogix-XT chassis
1,081,600
9.246E-07
1.0129E-03
—
1756-PB72/C
ControlLogix DC power supply
31,561,095
3.168E-08
3.4710E-05
—
1756-PA72/C
ControlLogix AC power supply
18,336,146
5.454E-08
5.9745E-05
—
1756-PA75/B
ControlLogix AC power supply
18,693,044
5.350E-08
5.8605E-05
—
1756-PA75R
ControlLogix AC redundant power supply
(8)
1,412,877
7.078E-07
7.7537E-04
—
1756-PB75/B
ControlLogix DC power supply
15,675,475
6.379E-08
6.9886E-05
—
1756-PB75R
ControlLogix DC redundant power supply
1,736,020
5.760E-07
6.3104E-04
—
1756-PAXT
ControlLogix-XT AC power supply
18,693,044
5.350E-08
4.0122E-08
—
1756-PBXT/B
ControlLogix-XT DC power supply
—
Summary of Contents for 1756-L6 Series
Page 24: ...24 Rockwell Automation Publication 1756 RM001I EN P May 2012 Chapter 1 SIL Policy Notes ...
Page 76: ...76 Rockwell Automation Publication 1756 RM001I EN P May 2012 Chapter 6 FLEX I O Modules Notes ...
Page 126: ...126 Rockwell Automation Publication 1756 RM001I EN P May 2012 Appendix D Checklists Notes ...
Page 133: ...Allen Bradley Motors ...