Industrial Engineer · phase 6 of 16
Safety PLC
Controller designed and certified to execute safety-related logic within specified SIL or PL limits.
The Explain card
- Plain English
- A safety PLC is a controller built and certified to run the logic that keeps people safe. Redundant processors, self testing, and a protected safety program let it reach a stated SIL or PL rating.
- Example
- Emergency stops, light curtains and guard door switches feed a safety controller. It removes power from the drives through safety outputs, and the standard PLC only gets told that it happened.
- Why it matters
- A standard PLC can fail with an output stuck on and never know. A safety PLC is designed to detect its own faults and go to the safe state, which is the whole reason the safety function can be trusted to it.
- Hook
- The controller whose job is to doubt itself.
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.
