Glossary · Protective devices and interlocks
Interlock
Also known as: interlocking device
German: Verriegelung
In machine safety, an interlock is a device or logic function that prevents or stops hazardous operation when specified conditions are not met, for example when a guard is open or a required state has not been reached.
- Machine safety
- Technical documentation
In one sentence
An interlock prevents or stops hazardous operation until conditions such as a closed guard are met; it is a safety function to design, verify and test.
Example
On an integrated production line, an interlock prevents the transfer robot from entering the press area until the press signals that its ram is at top dead center and stopped.
How it applies
- Machine safety: Interlocks are most often associated with movable guards (interlocking guard), but they also coordinate machines, for example by preventing one machine from moving into an area another machine occupies.
- Functional safety: An interlock that protects people is a safety function. Its required Performance Level or SIL comes from the risk assessment, and its design must be verified and validated.
- Integrated systems: Interlocks between machines cross an interface. The signals, their meaning and the failure behavior must be specified on both sides.
- Technical documentation: List interlocks with their conditions and reactions, describe the periodic test, and state that bypassing is prohibited.
Interlock vs. process interlock
Not every interlock is safety-related. Process interlocks protect product or equipment and may be implemented in standard control logic. Only interlocks that reduce risk to people must meet safety integrity requirements; label the two kinds clearly.