Glossary · Functional safety
Safety relay
Also known as: safety relay module, safety monitoring relay
German: Sicherheitsrelais
In functional safety, a safety relay is a relay-based device designed to perform and monitor safety-related control functions. Typical safety relays monitor emergency stops, guard interlocks or light curtains, check their own contacts and prevent restart after a fault.
- Functional safety
- Integrated systems
In one sentence
A safety relay is a dedicated device that performs and monitors a fixed safety function such as an emergency stop or guard interlock.
Example
A small press uses a safety relay to evaluate the two-channel emergency stop and the guard switch, with monitored manual reset and feedback from the motor contactors.
How it applies
- Functional safety: A safety relay is the logic part of a safety function. The achieved level also depends on the sensors, actuators and wiring connected to it.
- Machine safety: Safety relays suit small machines with few functions. As functions multiply, a safety PLC is often easier to verify and document.
- Technical documentation: Document wiring, the configured function (for example manual reset or automatic start) and the monitored feedback. The operating manual should explain reset behavior in plain words.
- Evidence: Manufacturer data such as PFHd and permitted categories apply only to the wiring variants described in the device manual. Record the variant used.
Safety relay vs. standard relay
A standard relay just switches. A safety relay uses redundant, monitored contacts, detects faults such as welded contacts and blocks restart until the fault is cleared.