which corresponds to a characteristic frequency of about 30 to 50 khz this characteristic frequency can be monitored from outside of the file for all of the contained head disk interfaces an external vibration sensor 702 is attached to the actuator pivot bearing 704 this vibration sensor 702 may be an acoustic emission ae sensor an accelerometer or an ldv for example the disk file 706 is spun up and vibrational information from the ae sensor is provided to circuits for recording both the disk velocity 708 and characteristic frequencies 710 this information is then passed to logic 720 that evaluates whether or not all sliders 730 have cleared the disk 706 and thus whether the file should be accepted or rejected for example if it is determined the highest tolerable take off velocity is 8 meters sec then with a bump spacing of 100 microns the characteristic frequency will be 80 khz if there is any amplitude from the vibration sensor 702 at this frequency the drive can be rejected the evaluation logic 720 may include a frequency filter which can be used as a tracking filter this allows the characteristic frequency amplitude to be tracked as a function of disk velocity when the amplitude of the.