FILE PROTECT SYSTEM FOR MAGNETIC TAPE UNIT WITH SOLENOID FOR SENSING PRESENCE OR ABSENCE OR REEL RING

摘要

In a magnetic recording and reproducing unit the magnetic heads are enabled to write or erase a magnetic tape only if a reel ring is inserted in the reel of magnetic tape. The file protect system includes a solenoid which is momentarily energized after a reel is placed in the unit. The solenoid moves a plunger into a position which senses the presence or absence of a reel ring. The plunger momentarily actuates switch contacts if the plunger contacts a reel ring. The switch contacts set a latch having an output which enables the write and erase heads only if the latch is set. The file protect system is fail-safe because the latch is always reset when power is turned on or when a reel is removed. If there is failure of the file protect system the latch will remain reset insuring that the magnetic tape cannot be erased or written upon.