Providing Safety
Alpha and Bravo interlock blocking devices, how do they work?

What are ALPHA and BRAVO interlock blocking devices and how do they improve safety?

ALPHA and BRAVO are fully mechanical safety systems that regulate access to safeguarded areas. Both systems are designed to increase safety by preventing unintentional restarts of machines during operations.


The ALPHA is installed on doors that are already equipped with a safety switch or sensor. This system ensures that a door cannot be opened without the coded safety key. Operators must take this key with them when they enter the guarded area. As long as the key is not returned, the door cannot close and the machine stays locked. The ALPHA is suitable for both hinged and sliding doors and can be easily retro-fitted.

How does the ALPHA for hinged doors work?

  1. Close the door: Make sure the door is fully closed.
  2. Activate ALPHA interlock blocking device: Turn the uniquely coded safety key, then remove the safety key from the lock. The ALPHA containment protection now prevents the access door from opening.
  3. Block door closing: The ALPHA blocks door closing and door contacts switching until the safety key is inserted back into the lock.
  4. Open the door: Remove the safety key from the lock to open the door.
  5. Access the protected area: As long as the operator is present in the protected area with the safety key, the door cannot be closed and the machine cannot be restarted.
  6. Override protection: Insert the safety key back into the lock to reopen the door and restart the machine.

How does the ALPHA for sliding doors work?

  1. Door closed: The safety contacts are closed and the machine is in operation.
  2. Door partially open: The sliding door can be opened to a certain point, with the safety contacts opening.
  3. Fully open: Turning the key fully unlocks the door and allows the locking plate to move, preventing the door from being closed.
  4. Key removal: The key can be removed, and personal padlocks can be added for extra safety.
  5. Machine shutdown: As long as the key is removed, the safety contacts remain open and the machine cannot restart.


BRAVO prevents light curtains from being reset as long as someone is present in the protected zone. This system is specially designed to ensure that safety measures remain intact as long as the zone is occupied, preventing unwanted activation of machines.

The BRAVO interlock blocking device can be easily mounted with sliding nuts on the side of the light curtain. In addition, mounting on a guard profile is possible thanks to the blocking plates in various depths that are supplied as standard.

The coded key can only be removed when the blocking device interrupts the beams of the light curtain. The operator takes this safety key into the protected area, preventing unintentional restart or reset of the machine. If several operators enter the area, the spring-loaded dust cover can be fitted with two padlocks to prevent the key from being inserted and thus the blocking of the light beam.

Functioning BRAVO light curtains:

  1. Mounting the BRAVO containment guard: Place the BRAVO interlock blocking device next to or on the receiver of the light curtain with 2 fasteners.
  2. Activation of the blocking plate: Turn the key to activate the blocking plate for the light curtain, blocking the beams. The key can only be removed when the blocking plate blocks the light curtain.
  3. Personal protection against restart: Take the released key into the protected area as personal protection against unexpected restart. As long as the key is removed, the blocking plate remains locked.
  4. Application of safety padlocks: If several operators need to enter the protected zone, install safety padlocks to prevent the lockable dust cover from being opened and prevent restarting.

The ALPHA and BRAVO interlock blocking devices increase safety in secure zones by preventing machines from restarting when someone is in the secure zone. The ALPHA ensures that doors do not close without the safety key, while the BRAVO ensures that light curtains do not reset as long as someone is in the secure zone. Both systems can be easily installed on existing doors and light curtains and are crucial for a safe working environment.

If you’re interested in learning more about this topic, feel free to reach out to one of our sales engineers by contacting us here.

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