showstack / hardware / pilz-pnoz-safety-relay
Pilz PNOZ safety relay
The monitored safety relay that made two-channel emergency stop circuits ordinary. It watches both channels of the button, detects a discrepancy or a cross-fault between them, reads back the mirror contacts of the downstream contactors, and refuses to reset if any of it disagrees — which is the difference between a stop button and a safety function.
Connectors
- Dual-channel input terminals
- Positively guided output contacts
- Feedback loop
What to watch for
A safety relay is not a rating on its own. The Performance Level belongs to the whole function — button, wiring, logic, contactors and the mechanics they switch.
The feedback loop is not optional wiring. Without it a welded contactor is invisible and the redundancy is theatre.
A monitored reset needs a rising and a falling edge, which is why a taped-down reset button cannot arm the system.
Sources
- Pilz — Pilz primary
Understand the mechanism
Something wrong, or missing?
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