Industrial Engineer · phase 6 of 16
SIL
Safety Integrity Level, a discrete integrity target for safety functions under IEC 61508 and related sector standards.
The Explain card
- Plain English
- Safety Integrity Level is a number from 1 to 4 that says how much a safety function can be relied on to work when it is needed. Higher means a lower allowed probability of failure on demand.
- Example
- A process shutdown valve on a reactor is rated SIL 2. The sensors, the logic solver and the valve together have to meet that number, with the math to prove it.
- Why it matters
- SIL comes from IEC 61508 and its process industry child IEC 61511, and it is about the whole loop rather than any single part. Buying a SIL 3 controller does nothing for a loop with a single unproven sensor.
- Hook
- How much you are allowed to trust the safety function.
Where it sits in the deck
Phase 6: PLC Operating Modes, Safety, and Diagnostics
Run, program and fault: what a controller does when something goes wrong, and the safety functions that decide how much that costs.
