TH10524A - How can I measure magnetic properties without damaging the recording disk? - Google Patents

Abstract

This invention relates to a tool or device capable of determining, without damaging the magnetic properties of a recording disk, the underlying digital data recording capabilities of such disk. These measurements would include determining parameters such as magnetic attraction or magnetic field, and the magnetic retention thickness of the recording disk, which would be proportional to or a function of the disk's perimeter and/or radius. These parameters would determine the signal amplitude and frequency response of the recording disk.

Claims (13)

1. Method for Measuring the Magnetic Power of a Rotating Magnetic Disk in Magnetic Data Storage Devices. A rotating magnetic data storage disk has a number of data recording lines on its surface. To determine data recording positions, the storage device also includes a read/write head that can select the desired position on the recording line to record, access, and erase data at that position. The measurement method involves the following steps: recording data at a number of these recording positions on the disk; applying a sufficient negative DC field to erase the recorded signal at a given recording position; measuring the magnitude of the negative DC field required to reduce the recorded signal at a given recording position by 50% (6 dB); and calculating the magnetic power of the disk, which is a function or proportion of the measured negative DC field. 2. The method under claim 1 in which the magnetic field Hx is calculated as a function of the relationship (chemical formula) as follows: (chemical formula), where i is the current in amperes flowing through the read/write head used to erase the recorded data by 50% (6db), N is the number of turns of the head, g is the length of the gap in the head used to record the data, Aw is the efficiency of the read/write head, Y is the distance of the bottom of the head at which the effective magnetic force is measured, and Hx is the magnetic field in ersteds. 3. The method under claim 2, where Y is chosen by the sum of the distances from such segment to the surface of the disk plus 1/2 the thickness of the disk used for recording. 4. The method under claim 2 includes the following steps: positioning the header to the data recording location on the disk; measuring the magnetic field induced in the header by the magnetic poles on the disk representing the recorded data at that location; storing this measured induction field as the initial magnetic field; applying a DC current field for data erasure and measuring the induction signal until the measured induction signal is half the initial signal; and applying a magnetic field Hx to the required erasure field resulting in a halving of the signal size. 5. The method under claim 4 includes procedures for applying the negative DC current field to a measurably increasing level, measuring and storing the readout signal in the header, and increasing the negative DC current field until the readout signal is approximately 50% of the initial signal size. 6. The method under claim 5, where the increase in the negative applied DC field change is approximately 50 erstek. 7. The method under claim 6 includes an insertion procedure between data points at 50% of the readback level, where the break is much less than 50 erstakes. 8. The method under claim 5 includes the execution of procedures leading to a 50% reduction in size measurement at a certain number of such data recording locations on the said disk. 9. A system for determining the magnetic characteristics of a magnetic medium at known intersection points. This system comprises: a path for passing a recorded current through the recording head gap to record a series of separate magnetic transmissions at the known intersection points; a path for applying a negative DC field at any known intersection point by passing a certain current through the head, which can be determined by the following relationship (formula); a path for measuring the read-back signal obtained after the recording and subtraction steps at the intersection point; a path for increasing the applied negative DC field by an increasing amount after the recording and subtraction steps are reactivated; a path for defining the relationship between the read-back signal and the applied field; and a path for analyzing the relationship between the read-back signal and the applied field to select a point representing a 50% signal loss at any intersection point for determining the magnetic susceptibility of the medium. 10. A system under claim 9 that includes a method for responding to the specified writing method for selecting the negative DC current of -6dB of the said feedback signal and a method for calculating the magnetic force or attraction dependent on the said feedback signal. 11. Under Claim 9, which includes a procedure for responding to the aforementioned written procedure for selecting a half-pulse width value and a procedure for acting upon such half-pulse width value to calculate the magnetic retention thickness effect of the magnetic medium. 12. The method under patent 2 includes the procedure of selecting a half-pulse width value based on the calculated value of Hx, and then proceeding with that half-pulse width value to calculate the magnetic retention thickness of the magnetic medium. 13. Method pursuant to claim 12 where Pw50 (Position Width) = Resistor (Ap/Ep), Ap = Area under the separated pulse, Ep = Maximum size of such separated pulse.