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Testing the Writeability of a Magnetic Head

IP.com Disclosure Number: IPCOM000061526D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Heinrich, V: AUTHOR [+2]

Abstract

In a magnetic disk storage, the writeability of a magnetic head can be tested by erasing the disk in one magnetic direction and by writing a low-frequency pulse track on the disk by means of the head. The head then reads the amplitudes of the positive and the negative pulses on the disk, the ratio of these amplitudes being indicative of the head's symmetry (writeability). It has been found that the accuracy of the above-described method is impaired by small signal offsets in the electronic signal path and by small magnetic fields in the vicinity of the head. For improved accuracy, it is suggested that two measurements of the above-described kind be made, but with opposite DC saturation.

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Testing the Writeability of a Magnetic Head

In a magnetic disk storage, the writeability of a magnetic head can be tested by erasing the disk in one magnetic direction and by writing a low-frequency pulse track on the disk by means of the head. The head then reads the amplitudes of the positive and the negative pulses on the disk, the ratio of these amplitudes being indicative of the head's symmetry (writeability). It has been found that the accuracy of the above-described method is impaired by small signal offsets in the electronic signal path and by small magnetic fields in the vicinity of the head. For improved accuracy, it is suggested that two measurements of the above- described kind be made, but with opposite DC saturation. By mirroring one of the measured symmetry values on the 100% symmetry axis, as shown in the figure, and determining the mean value of the two measured symmetry values, the influence of the error sources mentioned can be eliminated. In the figure, R % is the ratio of the measured positive/negative amplitudes; 1 is the offset caused by the electronic measuring channel; 2 is the offset caused by an outer magnetic field; 3 is the true symmetry, i.e., the symmetry performance of the magnetic head; A is the symmetry measured for one magnetic DC erasure direction; B is the symmetry measured for the other erasure direction; C is the value B mirrored on the 100% axis; and D is the value of the true symmetry as the mean value of A and C.

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