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Improved Estimation of Flying Height Changes

IP.com Disclosure Number: IPCOM000035903D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Brown, BR: AUTHOR [+3]

Abstract

A method for measuring changes in flying height of a magnetic readback element uses signals written at two different wavelengths.

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Improved Estimation of Flying Height Changes

A method for measuring changes in flying height of a magnetic readback element uses signals written at two different wavelengths.

The signal written on a single track of a rotating storage device consists of sections of alternating types, one section written with the first wavelength (A), the other section written with the second wavelength (B). In order to estimate a change in flying height, it is first required to separately measure the amplitude of the signal at each wavelength. When this set of measurements is later repeated, the change in flying height during the intervening time can be computed.

The computation is highly sensitive to errors in the measured amplitudes. The method described here reduces the errors in the measured amplitudes and thus in the final result.

Earlier solutions to this problem encountered difficulties because of a need for synchronization. The analog-to-digital conversion process that measures the amplitudes of two different wavelengths in alternating sections, must switch accurately between the two sections. At the transition between sections, the frequency content is dynamic and unpredictable. If an accurate synchronization signal exists for each transition, then the measurement can be performed on intervals that exclude the transition regions. The solution described here does not require synchronization, and so is usable when no such signal is available.

The new method is as follows for wavelength A. An identical method applies to wavelength B. Analog bandpass filtering selects the portion of the signal on the track that is written with wavelength A. The objective is to perform an analog- to-digital conversion on this data and also eliminate measurements from the transitional points and from the portion of the track written with the other wavelength. The signal was written with constant amplitude at each wavelength. Thus, most of the values obtained after filtering are close to some high value V (when reading wavelength A) or are near zero (when reading wav...