Interlocking

Interlocking refers to a system or set of devices designed to coordinate actions so that unsafe or conflicting operations cannot occur. The core idea is to enforce a safe sequence of steps or to lock certain actions until prerequisite conditions are met, reducing the risk of accidents or damage in complex processes.

Types and mechanisms vary by application. Mechanical interlocks use physical barriers to block a operation until another operation is completed or a guard is in place. Electrical or electronic interlocks rely on circuits, relays, or safety controllers to prevent start-up or movement when conditions are not satisfied. Software interlocks implement logic in control programs to reject commands that would create an unsafe state. In railway signaling, a specialized form called signal interlocking locks signals and track switches (points) so that a route cannot be set in conflict with another; modern systems use fail-safe computerized logic and track circuits to maintain safety. In textiles, interlock refers to a type of double-knit fabric produced by interlocking two layers of loops, resulting in a fabric with smooth surfaces on both sides.

Applications are widespread. Interlocks are essential in railway operations, manufacturing automation, elevators and escalators, packaging lines, factory safety enclosures, and consumer electronics. They also appear in textiles as fabric construction. Design considerations typically emphasize fail-safe behavior, reliability, clear diagnostics, and, where appropriate, redundancy to maintain safe operation in the presence of faults.

History and standards: interlocking concepts emerged in the 19th century with railway signaling and have since evolved into computerized safety systems governed by industry standards and regulatory requirements to ensure predictable, verifiable behavior in critical applications.