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

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