Tape edge detector using off tape and on tape MR noise

摘要

A magnetic tape edge detector is provided which detects the edge of the tape by processing the noise power produced by an MR element when it is completely off the tape and the noise power produced by the MR element when it is completely on the tape. The off tape noise power is produced by factors intrinsic to the MR element and circuitry connected thereto, while the on tape noise power is produced by the heating of the MR element due to friction between moving magnetic tape and the MR element. The difference between the off tape noise power and the on tape noise power is divided by an integer greater than one to produce a reference noise signal. The reference noise signal represents a reference position of the MR element with respect to the edge of the tape. For instance, if the integer is two the MR element is at its reference position when the edge of the tape bisects the width of the MR element. The magnitude of off tape noise power is directly related to the width of the MR element. Once the reference position is detected the MR element or a plurality of interconnected MR elements can be indexed to desired information or servo tracks on the magnetic tape.