140 lines
2.2 KiB
Markdown
140 lines
2.2 KiB
Markdown
# EN 61508 — Functional Safety of E/E/PE Systems
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## Overview
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EN 61508 is the generic functional safety standard for Electrical / Electronic / Programmable Electronic (E/E/PE) systems.
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It provides a framework to ensure systems reduce risk to an acceptable level.
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---
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## Core Idea
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Risk is defined as:
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Risk = Frequency × Consequence
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Safety functions reduce this risk.
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---
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## Key Concepts
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### Safety Function
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A function that:
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- Detects hazardous conditions
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- Takes action to prevent harm
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---
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### Safety Integrity Level (SIL)
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| SIL | Meaning |
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|-----|--------|
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| SIL 1 | Low risk reduction |
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| SIL 2 | Moderate |
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| SIL 3 | High |
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| SIL 4 | Very high |
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---
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### Probability of Failure
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#### Low Demand Mode (PFDavg)
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| SIL | Range |
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|-----|-------|
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| SIL 1 | 1e-2 to 1e-1 |
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| SIL 2 | 1e-3 to 1e-2 |
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| SIL 3 | 1e-4 to 1e-3 |
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| SIL 4 | 1e-5 to 1e-4 |
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#### High/Continuous Mode (PFH)
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| SIL | Failures/hour |
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|-----|---------------|
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| SIL 1 | 1e-6 to 1e-5 |
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| SIL 2 | 1e-7 to 1e-6 |
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| SIL 3 | 1e-8 to 1e-7 |
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| SIL 4 | 1e-9 to 1e-8 |
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[PFD_PFH_when_to_use](PFD_PFH_when_to_use.md)
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[PFD_and_PFH](PFD_and_PFH.md)]
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---
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## Safety Lifecycle
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1. Hazard analysis
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2. Safety requirements
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3. System design
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4. Hardware design
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5. Software design
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6. Verification & validation
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7. Operation & maintenance
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8. Decommissioning
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---
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## Hardware Reliability
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- FIT = 1e-9 failures/hour
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- PFH = Probability of dangerous failure/hour
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- PFDavg = Probability of failure on demand
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---
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## Failure Types
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### Random Failures
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Handled statistically (FIT, PFH)
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### Systematic Failures
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Handled by process, reviews, and discipline
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---
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## Techniques
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- Redundancy (1oo2, 2oo3)
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- Diagnostics
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- Diversity
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- Formal methods (high SIL)
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---
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## Standard Structure
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1. General
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2. Hardware
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3. Software
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4. Definitions
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5–7. Guidelines
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---
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## Related Standards
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- EN 61511 (Process)
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- EN 62061 (Machinery)
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- ISO 26262 (Automotive)
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- EN 298 (Burners)
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---
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## Key Takeaways
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- Focus on risk reduction
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- SIL is a target, not a feature
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- Process matters as much as maths
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- Lifecycle coverage is essential
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---
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## One-Line Summary
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EN 61508 ensures safety systems reduce risk using quantified reliability and disciplined engineering processes.
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---
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