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Browse Prior Art Database

Acoustical Interference Detector

IP.com Disclosure Number: IPCOM000090984D
Original Publication Date: 1969-Sep-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Schaefer, WC: AUTHOR

Abstract

The system detects acoustical sound that is emitted as a result of physical contact between a rapidly rotating disk surface and a fixed magnetic head. Microphone 10 is used as the sensor, together with electronic circuitry which selects portions of acoustical information that are peculiar to head-to-disk interference HDI.

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Acoustical Interference Detector

The system detects acoustical sound that is emitted as a result of physical contact between a rapidly rotating disk surface and a fixed magnetic head. Microphone 10 is used as the sensor, together with electronic circuitry which selects portions of acoustical information that are peculiar to head-to-disk interference HDI.

Sound waves, generated as a result of HDI, impinge on microphone 10 and its output is amplified by preamplifier 12. The amplified sound is applied to bandpass filter 14. Only those frequencies characteristic of HDI are passed. The passed frequency signals are directed to automatic gain control AGC 16. This keeps the average peak-to-peak signal amplitude relatively constant. AGC 16 boosts the average p-p signal amplitude to approximately 3 volts.

AM detector 18, coupled in a feedback loop with AGC 16, provides a signal which is equal to the rectified envelope of the input signal to such detector. The envelope signal is processed through low-pass filter 20 which has a time constant equal to about 15 seconds. The output of filter 20 is a slowly varying DC reference voltage which represents the average value of the background noise level received by microphone 10. This reference voltage enters the reference side A of floating comparator 22. This device is such that, if point B in the input line to comparator 22 exceeds point A by three volts, such comparator changes state. Point B receives the fast-changing envelope voltage from detector 18. This fast-changing envelope represen...