Abstract: 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.

Abstract: The invention relates to an optoelectronic scanning arrangement for scanning optical markings. The optical markings consist of a reflecting mark RM and a non-reflecting mark NM which is inclined by an angle W from the axis of the pencil of rays radiated from a light source LS.

Abstract: A device is disclosed for suppressing deviations in the output voltage of a pressure transducer in magnetic tape recorders caused by temperature fluctuations. A voltage dependent on the temperature of the pressure transducer is connected to the adjustable tap of a potentiometer connected between inputs of a differential amplifier. An operational amplifier compensates the output voltage of the pressure transducer with the output of the differential amplifier.