Dependability Theory and Methods Part 4: Fault-tree analysis

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Dependability Theory and MethodsPart 4
Fault-tree analysis

• Andrea Bobbio
• Dipartimento di Informatica
• Università del Piemonte Orientale, A. Avogadro
• 15100 Alessandria (Italy)
• bobbio_at_unipmn.it - http//www.mfn.unipmn.it/bob
  bio

Bertinoro, March 10-14, 2003
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Elements of logic algebra
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Elements of logic algebra
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Elements of logic algebra
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Logic algebra and Venn diagrams
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Fundamental assumptions for FTA

• Events are binary events (working/non-working)
• Events are statistically independent
• Relationships between events and causes are
  represented by logical AND and OR (Boolean)
  gates
• The root of the FT is the catastrophic undesired
  event called the Top Event (TE).

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Case study a PLC architecture
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Case study a PLC architecture
The considered failure rates for the elementary
blocks are reported in the Table.
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PLC architecture FTA
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Safety and dependability measures

• Safety assessment of the control system
  according to IEC 61508 (Functional safety of
  electrical/electronic/ programmable electronic
  safety-related systems)
• SIL requirements (IEC 61508)
• Unreliability versus time
• Safe Mission Time (SMT)
• Mean Time To Failure
• Critical failure path (mcs).

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FT Critical cuts
The FT has 59 MCS, one of order 1 (the voter) and
the remaining 58 of order 2.