Write enable ring sensing arrangement for a magnetic tape reel

摘要

In order to be able to write in a magnetic tape inserted in a magnetic tape recorder, a write enable ring must be inserted on the rear of the magnetic tape reel. The presence and absence of the write enable ring is checked through the use of a sensing ring which is displaced in the axial direction when the tape reel having the write enable ring is put in place. At its exterior, the sensing ring has a surface in the axial direction having high reflectivity and contains a mark having low reflectivity. The presence and absence of the write enable ring is statically checked with an opto-electronic sensing element by sensing the surface having high reflectivity and dynamically checked by sensing the mark.