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How to develop E/E/PESs to IEC 61508?

How to develop E/E/PESs to IEC 61508?. E/E/PES is: electrical/electronic/programmable electronic system IEC 61508-4 subclause 3.3.3. What is the safety question?. How to make a product safe, or How to make a safe product?. What is safety? How do you measure it?.

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How to develop E/E/PESs to IEC 61508?

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  1. How to develop E/E/PESs to IEC 61508? E/E/PES is: electrical/electronic/programmable electronic system IEC 61508-4 subclause 3.3.3

  2. What is the safety question? How to make a product safe, or How to make a safe product?

  3. What is safety? How do you measure it?

  4. Safety: “freedom from unacceptable risk” Harm to: probability of occurrence people property environment safety people property severity of occurrence environment

  5. What is a Risky System? A system with an unacceptable combination of: probability of occurrence of harm and the severity of that harm.

  6. IEC 61508 safety theory is - remove systematic defects IEC 61508 implies: ad hoc or non-safety processes  non-safety products non-safety processes – systematic defects  safety processes safety processes  safety products safety processes + functional safety assessment  IEC 61508 compliance

  7. The Safety Equation MTBF = MTBRF + MTBSF PFD = PRFD + PSFD safety integrity = hardware safety integrity + systematic safety integrity MTBF - Mean Time Between Failure MTBRF - Mean Time Between Random Failure MTBSF - Mean Time Between Systematic Failure PFD - Probability of Failure on Demand PRFD - Probability of Random Failure on Demand PSFD - Probability of Systematic Failure on Demand

  8. Safety Measurements MTBF = 1/(failure rate) failure rate = RHF + SHF + SSF SIL  1/(failure rate) SIL  1/(RHF + SHF + SSF) RHF - Random Hardware Failure SHF - Systematic Hardware Failure SSF – Systematic Software Failure SIL - Safety Integrity Level See IEC 61508-1, Tables 2 and 3

  9. Relationship of IEC 61508 to failure type random hardware failure (RHF) see IEC 61508-2 systematic hardware failure (SHF) see IEC 61508-2 systematic software failure (SSF) see IEC 61508-3

  10. Systematic defects Systematic defects are removed during the product development lifecycle The product development lifecycle is depicted graphically with the V-model The V-model for software development is shown in Figure 5 of IEC 61508-3

  11. The Parts of IEC 61508 IEC 61508-1 Part 1: General requirements IEC 61508-2 Part 2: Requirements for electrical/electronic/programmable electronic safety-related systems IEC 61508-3 Part 3: Software requirements IEC 61508-4 Part 4: Definitions and abbreviations IEC 61508-5 Part 5: Examples of methods for the determination of safety integrity levels IEC 61508-6 Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3 IEC 61508-7 Part 7: Overview of techniques and measures

  12. Non-complex or Complex system? Non-complex  deterministic system A deterministic system has a unique output for each specific input Complex  non-deterministic system A non-deterministic system means that the system output is a function of the current input and the previous output.

  13. IEC 61508-3 Software Requirements Example From the E/E/PES hardware development processes, it has been determined that a microcontroller is required to implement the complex logic in software, (See IEC 61508-3 Figure 1) and SIL 3 has been determined IEC 61508-3, clause 7.2, Software safety requirements specification, points to IEC 61508-3, Table A.1 IEC 61508-3, Table A.1, Software safety requirements specification, points to IEC 61508-7, Technique/Measure B.2.4 IEC 61508-7, Technique/Measure B.2.4, describes Computer-aided specification tools

  14. WHY NOT ENGINEERING www.whynotengineering.com

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