SafetyInterlocks

Safety interlocks are devices or systems designed to ensure a safe state for industrial equipment by preventing machine operation or access to hazards until specified safety conditions are met. They are a core element of safety-related control systems and help reduce the risk of injury during setup, maintenance, and operation.

Interlocks can take several forms. Mechanical interlocks use physical latching or guarding mechanisms to block access or start-up. Electrical or electronic interlocks employ switches, relays, or safety controllers to monitor guards and doors and to interrupt power or motion if a safety condition is breached. Software-based interlocks, implemented in programmable logic controllers, can coordinate complex safety logic and interlock sequences. Many interlocks are monitored, providing diagnostic signals that verify the interlock components themselves are functioning correctly.

Common applications include guarding on presses, shears, conveyors, and robotic work cells, where a door or gate must be closed, a guard must be in place, or a safety sensor must indicate a safe condition before machine startup or movement is allowed. Interlocks may be non-latching, allowing immediate reset after a stop condition, or latching, which requires a deliberate action to re-enable operation after a fault or open condition.

Standards and risk assessment underpin interlock design. ISO 14119 covers mechanical interlocks, while IEC 62061 and ISO 13849-1 address safety-related electrical control systems and performance levels. Designers aim for fail-safe behavior, regular maintenance, and clear dependency between the interlock and the machine’s safety function.

Maintenance and testing are essential. Regular inspection of mechanical wear, electrical integrity, and software updates, along with periodic functional tests, help ensure ongoing effectiveness and compliance. Documentation of safety ratings and test results supports verification and audits.