Glossary · Protective devices and interlocks
Protective device
German: Schutzeinrichtung
In machine safety, a protective device is a safeguard other than a guard that reduces risk by detecting a person, controlling access or initiating a protective function, either alone or in combination with a guard.
- Machine safety
- Risk assessment
In one sentence
A protective device is any safeguard other than a guard, such as a light curtain, interlock or two-hand control; it acts through the control system.
Example
A robot cell uses a fixed fence as its guard and, as protective devices, an interlock on the access door and a safety laser scanner at the loading station.
How it applies
- Machine safety: In the three-step method of ISO 12100, guards and protective devices together form safeguarding, the second step after inherently safe design. Protective devices are chosen where frequent access is needed or where guards are impractical. See risk reduction.
- Functional safety: Most protective devices act through the control system, so they form part of a safety function whose Performance Level or SIL must match the risk.
- Technical documentation: Protective devices are measures built into the machine. Information for use describes how to use and test them, but it does not replace them.
- Evidence: Record for each device the hazard it addresses, its required and achieved safety integrity, and its verification.
Protective device vs. guard
A guard is a physical barrier. A protective device detects, restrains or controls; it lets a person approach and reacts to them, for example by stopping the machine.