Protecting door locks to areas

摘要

During operation of a hazardous process, entry doors to an enclosure containing the process are locked to prevent entry of personnel. The keys (26,28) are inserted into the safety unit locks (32,34) which contain sliding pins (36,38) which engage holes (48,50) in a sliding element (54), moved by an electro-magnet (44) along a track (52), when the process is in a safe state. When a key is turned the pin is retracted and the key locked in the lock. Electrical energy may then be supplied to the machine or process through contacts (58) on the magnet and the slider (54) prevents the pins being returned to a position permitting the keys to be turned. A time delay function may be included to accommodate machine run-down time.