# Dependability Theory and Methods Part 4: Fault-tree analysis - PowerPoint PPT Presentation

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Dependability Theory and Methods Part 4: Fault-tree analysis. Andrea Bobbio Dipartimento di Informatica Universit à del Piemonte Orientale, “ A. Avogadro ” 15100 Alessandria (Italy) bobbio@unipmn.it - http://www.mfn.unipmn.it/~bobbio. Bertinoro, March 10-14, 2003.

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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@unipmn.it - http://www.mfn.unipmn.it/~bobbio

Bertinoro, March 10-14, 2003

Bertinoro, March 10-14, 2003

Elements of logic algebra

Elements of logic algebra

Elements of logic algebra

Logic algebra and Venn diagrams

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).

### Case study: a PLC architecture

Bertinoro, March 10-14, 2003

### Case study: a PLC architecture

The considered failure rates for the elementaryblocks are reported in the Table.

Bertinoro, March 10-14, 2003

PLCarchitecture: FTA

Bertinoro, March 10-14, 2003

Safety and dependability measures

• Safety assessment of the control systemaccording to IEC 61508 (Functional safety ofelectrical/electronic/ programmable electronic safety-relatedsystems)

• SIL requirements (IEC 61508);

• Unreliability versus time;

• Safe Mission Time (SMT);

• Mean Time To Failure;

• Critical failure path (mcs).

Bertinoro, March 10-14, 2003

FT Critical cuts

The FT has 59 MCS, one oforder 1 (the voter) and theremaining 58 of order 2.

Bertinoro, March 10-14, 2003