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BEMF - Motor Sensing Interlock

•   Motor sensing interlock
•   Designed to control access to rotating machinery
•   Relies on the measurement of the electromotive force generated by the windings of an electric motor
•   Only when the motor has stopped will the BEMF drop to zero and allow the release of a key
•   The unit is used for connection to AC and DC motors including DC braking systems
•   Designed to provide the highest level of safety when installed as part of an access control system for dangerous machinery
•   Available with FS or Q type lock portions


The BEMF is designed to operate as part of an integrated safety system. The BEMF controls access to hazardous areas with rotating machinery.

When the electric motor is running, the key of the BEMF interlock cannot be removed, hence preventing access to the hazardous area. To gain access to the area, the electrical motor must be switched off by turning the key to OFF position. This changes the switches of the electrical supply to the machine to a safe condition. Only when the motor has stopped will the BEMF drop to zero and allow the release of a key. A green LED illuminates. By pushing the green button, the key can now be removed and taken by the personnel to the AI access interlock.

The guard can only be opened when the electrical supply has been switched into a safe condition. The machine cannot be restarted until the door is closed and the key is removed and taken to the BEMF motor sensing unit.

  Type   1 2   3   4   5 6   7      
Part Number BEMF -     -   -   -     -        
Example BEMF - FS B - F - 3 - 110 A - TBA      

1 Lock portion type FS / Q
2 Material B = Brass, standard
3 Mounting F = Front of board mount with enclosure, standard
4 Number of poles 3, standard
5 Voltage 24 / 110 / 240, standard
6 Current AC (use for 110V and 240V) / DC (use for 24V)
7 Lock portion symbol FS up to 3 characters / Q up to 6 characters