Catalogs > Safety Products Catalog > Principles, Standards and Implementation > System Design According to ISO/EN 13849 and SISTEMA
System Design According to ISO/EN 13849 and SISTEMA
| SISTEMA Software PL Calculation Tool |  |
System Structure | |
Reliability Data | |
Methods of Data Determination | |
Diagnostic Coverage | |
Common-Cause Failure | |
Mission Time | |
| Systematic Faults | |
Fault Exclusion | |
Performance Level (PL) | |
Subsystem Design and Combinations | |
Validation | |
Machine Commissioning | |
The performance level is a discrete level that specifies the ability of the safety-related parts of the control system to perform a safety function.
In order to assess the PL achieved by an implementation of any of the five designated architectures, the following data is required for the system (or subsystem):
- MTTFd (mean-time-to-dangerous failure of each channel)
- DC (diagnostic coverage)
- Architecture (the category)
Table 12 shows the PL achieved by various combinations. Refer to Annex K of the standard for more precise determination.
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| Figure 133: Graphical Determination of PL |
Table 12 shows the PL achieved by various combinations. Refer to Annex K of the standard for more precise determination. For example, an application uses the Category 3 designated architecture. If the DC is between 60% and 90%, and if the MTTFd of each channel is between 10 and 30 years, then according to Figure 133, PLd is achieved.
Other factors must also be realized to satisfy the required PL. These requirements include the provisions already discussed such as for common cause failures, systematic failure, and mission time.
If the PFHD of the system or subsystem is known, Table 12 (Annex K of the standard) can be used to derive the PL.
| MTTFd for each channel | Average probability of a dangerous failure per hour (1/h) and corresponding performance level (PL) | |||||||||||||
| Cat. B | PL | Cat. 1 | PL | Cat. 2 | PL | Cat. 2 | PL | Cat. 3 | PL | Cat. 3 | PL | Cat. 4 | PL | |
| Years | DCavg = none | DCavg = none | DCavg = low | DCavg = medium | DCavg = low | DCavg = medium | DCavg = high | |||||||
| 3 | 3,80 x 10-5 | a | 2,58 x 10-5 | a | 1,99 x 10-5 | A | 1,26 x 10-5 | a | 6,09 x 10-6 | b | ||||
| 3,3 | 3,46 x 10-5 | a | 2,33 x 10-5 | a | 1,79 x 10-5 | A | 1,13 x 10-5 | a | 5,41 x 10-6 | b | ||||
| 3,6 | 3,17 x 10-5 | a | 2,13 x 10-5 | a | 1,62 x 10-5 | a | 1,03 x 10-5 | a | 4,86 x 10-6 | b | ||||
| 3,9 | 2,93 x 10-5 | a | 1,95 x 10-5 | a | 1,48 x 10-5 | a | 9,37 x 10-6 | b | 4,40 x 10-6 | b | ||||
| 4,3 | 2,65 x 10-5 | a | 1,76 x 10-5 | a | 1,33 x 10-5 | a | 8,39 x 10-6 | b | 3,89 x 10-6 | b | ||||
| 4,7 | 2,43 x 10-5 | a | 1,60 x 10-5 | a | 1,20 x 10-5 | a | 7,58 x 10-6 | b | 3,48 x 10-6 | b | ||||
| 5,1 | 2,24 x 10-5 | a | 1,47 x 10-5 | a | 1,10 x 10-5 | a | 6,91 x 10-6 | b | 3,15 x 10-6 | b | ||||
| 5,6 | 2,04 x 10-5 | a | 1,33 x 10-5 | a | 9,87 x 10-6 | b | 6,21 x 10-6 | b | 2,80 x 10-6 | c | ||||
| 6,2 | 1,84 x 10-5 | a | 1,19 x 10-5 | a | 8,80 x 10-6 | b | 5,53 x 10-6 | b | 2,47 x 10-6 | c | ||||
| 6,8 | 1,68 x 10-5 | a | 1,08 x 10-5 | a | 7,93 x 10-6 | b | 4,98 x 10-6 | b | 2,20 x 10-6 | c | ||||
| 7,5 | 1,52 x 10-5 | a | 9,75 x 10-6 | b | 7,10 x 10-6 | b | 4,45 x 10-6 | b | 1,95 x 10-6 | c | ||||
| 8,2 | 1,39 x 10-5 | a | 8,87 x 10-6 | b | 6,43 x 10-6 | b | 4,02 x 10-6 | b | 1,74 x 10-6 | c | ||||
| 9,1 | 1,25 x 10-5 | a | 7,94 x 10-6 | b | 5,71 x 10-6 | b | 3,57 x 10-6 | b | 1,53 x 10-6 | c | ||||
| 10 | 1,14 x 10-5 | a | 7,18 x 10-6 | b | 5,14 x 10-6 | b | 3,21 x 10-6 | b | 1,36 x 10-6 | c | ||||
| 11 | 1,04 x 10-5 | a | 6,44 x 10-6 | b | 4,53 x 10-6 | b | 2,81 x 10-6 | c | 1,18 x 10-6 | c | ||||
| 12 | 9,51 x 10-6 | b | 5,84 x 10-6 | b | 4,04 x 10-6 | b | 2,49 x 10-6 | c | 1,04 x 10-6 | c | ||||
| 13 | 8,78 x 10-6 | b | 5,33 x 10-6 | b | 3,64 x 10-6 | b | 2,23 x 10-6 | c | 9,21 x 10-7 | d | ||||
| 15 | 7,61 x 10-6 | b | 4,53 x 10-6 | b | 3,01 x 10-6 | b | 1,82 x 10-6 | c | 7,44 x 10-7 | d | ||||
| 16 | 7,31 x 10-6 | b | 4,21 x 10-6 | b | 2,77 x 10-6 | c | 1,67 x 10-6 | c | 6,76 x 10-7 | d | ||||
| 18 | 6,34 x 10-6 | b | 3,68 x 10-6 | b | 2,37 x 10-6 | c | 1,41 x 10-6 | c | 5,67 x 10-7 | d | ||||
| 20 | 5,71 x 10-6 | b | 3,26 x 10-6 | b | 2,06 x 10-6 | c | 1,22 x 10-6 | c | 4,85 x 10-7 | d | ||||
| 22 | 5,19 x 10-6 | b | 2,93 x 10-6 | c | 1,82 x 10-6 | c | 1,07 x 10-6 | c | 4,21 x 10-7 | d | ||||
| 24 | 4,76 x 10-6 | b | 2,65 x 10-6 | c | 1,62 x 10-6 | c | 9,47 x 10-7 | d | 3,70 x 10-7 | d | ||||
| 27 | 4,23 x 10-6 | b | 2,32 x 10-6 | c | 1,39 x 10-6 | c | 8,04 x 10-7 | d | 3,10 x 10-7 | d | ||||
| 30 | 3,80 x 10-6 | b | 2,06 x 10-6 | c | 1,21 x 10-6 | c | 6,94 x 10-7 | d | 2,65 x 10-7 | d | 9,54 x 10-8 | e | ||
| 33 | 3,46 x 10-6 | b | 1,85 x 10-6 | c | 1,06 x 10-6 | c | 5,94 x 10-7 | d | 2,30 x 10-7 | d | 8,57 x 10-8 | e | ||
| 36 | 3,17 x 10-6 | b | 1,67 x 10-6 | c | 9,39 x 10-7 | d | 5,16 x 10-7 | d | 2,01 x 10-7 | d | 7,77 x 10-8 | e | ||
| 39 | 2,93 x 10-6 | c | 1,53 x 10-6 | c | 8,40 x 10-7 | d | 4,53 x 10-7 | d | 1,78 x 10-7 | d | 7,11 x 10-8 | e | ||
| 43 | 2,65 x 10-6 | c | 1,37 x 10-6 | c | 7,34 x 10-7 | d | 3,87 x 10-7 | d | 1,54 x 10-7 | d | 6,37 x 10-8 | e | ||
| 47 | 2,43 x 10-6 | c | 1,24 x 10-6 | c | 6,49 x 10-7 | d | 3,35 x 10-7 | d | 1,34 x 10-7 | d | 5,76 x 10-8 | e | ||
| 51 | 2,24 x 10-6 | c | 1,13 x 10-6 | c | 5,80 x 10-7 | d | 2,93 x 10-7 | d | 1,19 x 10-7 | d | 5,26 x 10-8 | e | ||
| 56 | 2,04 x 10-6 | c | 1,02 x 10-6 | c | 5,10 x 10-7 | d | 2,52 x 10-7 | d | 1,03 x 10-7 | d | 4,73 x 10-8 | e | ||
| 62 | 1,84 x 10-6 | c | 9,06 x 10-7 | d | 4,43 x 10-7 | d | 2,13 x 10-7 | d | 8,84 x 10-8 | e | 4,22 x 10-8 | e | ||
| 68 | 1,68 x 10-6 | c | 8,17 x 10-7 | d | 3,90 x 10-7 | d | 1,84 x 10-7 | d | 7,68 x 10-8 | e | 3,80 x 10-8 | e | ||
| 75 | 1,52 x 10-6 | c | 7,31 x 10-7 | d | 3,40 x 10-7 | d | 1,57 x 10-7 | d | 6,62 x 10-8 | e | 3,41 x 10-8 | e | ||
| 82 | 1,39 x 10-6 | c | 6,61 x 10-7 | d | 3,01 x 10-7 | d | 1,35 x 10-7 | d | 5,79 x 10-8 | e | 3,08 x 10-8 | e | ||
| 91 | 1,25 x 10-6 | c | 5,88 x 10-7 | d | 2,61 x 10-7 | d | 1,14 x 10-7 | d | 4,94 x 10-8 | e | 2,74 x 10-8 | e | ||
| 100 | 1,14 x 10-6 | c | 5,28 x 10-7 | d | 2,29 x 10-7 | d | 1,01 x 10-7 | d | 4,29 x 10-8 | e | 2,47 x 10-8 | e | ||
| Table 12: Precise MTTFd to Determine PL | ||||||||||||||
Source of Table 12 is Table K.1 of ISO/EN 13849-1:2006