Slider-disk clearance measurements in magnetic disk drives using the readback transducer

A method is described for noninvasively measuring the mechanical clearance between a head slider and the recording medium in magnetic storage devices. The method is based on detection of the pulse width of the output signal of the readback transducer. It is shown that a variation in clearance produces a proportional variation in pulse width. The proportionality factor can be determined by simulating the effect of the varying spacing loss on a digitized isolated impulse response typical for the head-disk combination under investigation. Instrumentation is presented that provides an analog output voltage which is a measure for the ratio (PW_x/T) of athe pulse width at the x% level (PW_x) and the repetition period (T) of the readback signal. With this instrumentation, the absolute slider-disk clearance can be determined by evacuating the air from the head-disk interface. The bandwidth of the instrumentation is such that clearance dynamics can also be measured. This allows the detection of glide defects, in situ in a fully operational storage device. Examples of these clearance and glide measurements are given for hard disk drives