Patent ID: 8018669

Claim:
A method for detecting touchdown between a magnetic head and a recording medium, comprising: driving the magnetic head to multiple positions that are successively closer to the recording medium until touchdown is detected; determining a position error signal for each of the multiple positions; converting each of the position error signals from a time domain into a frequency domain; computing a combined variance value from variances in the position error signals with respect to a baseline position error signal at each of a discrete number of frequencies that are within one or more selected frequency bands in the frequency domain; and detecting touchdown when the difference between the average combined variance value for N1 positions of the magnetic head and a baseline average exceeds a threshold value, where N1 is two or more, wherein the N1 positions of the magnetic head include one of the multiple positions that is closest to the recording medium and the remaining N1-1 positions are successively the next closest to the recording medium, and wherein the baseline average is an average of the combined variance value for N2 positions of the magnetic head that are different from the N1 positions, and the N2 positions are all further away from the recording medium than the N1 positions.