DeadManRelais

DeadManRelais is a safety device concept and implementation that uses a relay-based mechanism to enforce operator presence or regular input to keep a controlled process active. If the expected signal is not received within a defined interval, the device triggers a safe shutdown, alarm, or other protective action.

The term combines the idea of a dead man’s switch with the French word relais, reflecting a relay-driven approach to safety interlocking. It is used in some European and technical communities to describe a compact, relay-based solution as an alternative to purely microcontroller-driven safety circuits.

Operation and design: The core is a timer-front-end and a relay that controls the machine circuit. In normal operation, periodic pulses or a maintained signal reset the timer. Loss of input causes the relay to change state, opening or closing a circuit to stop the process. Many designs incorporate redundancy, fail-safe contacts (normally closed in the de-energized state), manual reset, and watchdog monitoring to detect sensor or power faults. Some implementations layer additional interlocks with other safety devices to meet reliability criteria.

Applications: DeadManRelais devices are used in industrial automation, heavy machinery, laboratory equipment, and robotics to ensure automatic shutdown if an operator is incapacitated or if control signals fail. They can be implemented as standalone relays or integrated with PLCs, controllers, or safety interlocks.

Limitations and safety considerations: Like any safety device, DeadManRelais designs must conform to relevant standards and be properly maintained. Potential issues include nuisance trips, delayed stopping, contact wear, and single-point failures if redundancy is not provided. The term should not be conflated with emergency stop devices, which have distinct hazard analysis requirements.