Interlocks into the machine’s control system to stop operation when the sensing filed (photoelectric, radio frequency, or electromagnetic) is disturbed.
Advantages: adjust to fit different stock sizes; allows access to load and unload the machine; and allows access to the guarded area for maintenance and set-up activities.
Disadvantages: Restricted to machines that stop operating cycle before operator can reach into danger area (e.g., machines with partial revolution clutches or hydraulic machines); Must be carefully maintained and adjusted; does not protect operator in the event of a mechanical failure; and operator may make device ineffective.
There are also presence-sensing mats that interlock into machine’s control system to stop operation when a predetermined weight is applied to the mat. A manual reset switch must be located outside the protected zone.