Patent ID: 8331049

Claim:
A hard disk drive, comprising: a disk base; a spindle motor mounted on said disk base and rotably coupled to at least one disk to create at least one rotating disk surface including multiple tracks each intersecting multiple servo wedges at an Amplitude Gain Control (AGC) calibration pattern; a head stack assembly pivotably mounted by an actuator pivot to said disk base and configured position a slider on said rotating disk surface to read said AGC calibration pattern to create a read AGC pattern signal; and a control circuit configured to receive a version of said read AGC pattern signal to create a Servo AGC (SAGC) sequence for said track, process said SACG sequence for said track to remove a repeatable component of said SAGC sequence to create a non-repeatable SAGC component, calculate a standard deviation for said non-repeatable SAGC component, and determine touch down of said slider on said rotating disk surface based upon said standard deviation exceeding a predetermined amount.