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Browse Prior Art Database

Quick Hc Pass/ Fail Test at SDT for Magnetic Disks

IP.com Disclosure Number: IPCOM000122077D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 49K

Publishing Venue

IBM

Related People

McNeil, WD: AUTHOR [+2]

Abstract

Described is a pass/fail method to check a disk for the following magnetic layer remnant coercivity values (Hc). - Hc min for any spot on the disk - Hc min average over the surface of the disk - Hc max average over the surface of the disk - Hc max for any spot on the disk.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 78% of the total text.

Quick Hc Pass/ Fail Test at SDT for Magnetic Disks

      Described is a pass/fail method to check a disk for the
following magnetic layer remnant coercivity values (Hc).  - Hc min
for any spot on the disk
-  Hc min average over the surface of the disk
-  Hc max average over the surface of the disk
-  Hc max for any spot on the disk.

      The hardware used in this test method is as noted in the
figure.  The procedure used to make these measurements is as follows:
-  Write with the read/write head 2 a low frequency signal with
current large enough to saturate the disk 3.  Measure the track
average and digitize the readback envelope at n positions.  Save
these values.
-  Apply the 4 Hc levels described above to the disk with external
magnet 1 starting at the lowest Hc (Hc min for any spot) and moving
successively to the highest Hc (Hc max for any spot).  Take the track
average and n envelope values at each applied field.  The n envelope
values are taken at the same position on the disk each time.  All the
values are saved.  The disk is checked to the Hc limits specified as
follows:
   -  Check the n digitized values at the lowest applied Hc. If any
value was reduced by more than 50 percent, the disk fails the Hc for
any spot criteria.  Otherwise, it passes this criteria.
   -  Check the track average value at Hc average min.  If it has
been reduced by more than 50 percent, the disk fails the Hc min.
average criteria.  Otherwise, it passes.
  ...