Evaluation of capacitance displacement sensors used for slider-disk spacing measurements in magnetic disk drives

Abstract

In a previous work, the authors (1991) compared head-disk spacing measurements in a magnetic hard disk drive that were made by a multichannel laser interferometer (MCLI) with those made simultaneously by capacitance probes (CP) embedded the air bearing surfaces of the slider. The flying height was determined through the contact-start-stop (CSS) process by averaging the spacing over one disk revolution during steady-state flying. In the present work, the authors show why a different calibration of the CP is needed for flying height and spacing variation measurements, and they derive an expression that gives the calibration factor as a function of the relative length of the CP to the slider's length. They also explain why the CP measurement appears to give an erroneous dependence of spacing variation on flying height.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>