Impact detector

Claim 2

An impact detector device for detecting impact between a record or replay head and a magnetic disc rotating relative to the head comprising a piezo-electric element having a resonant frequency mounted on or adjacent said head and producing an electrical output signal at its resonant frequency when said head contacts or is contacted by said disc, amplifying means having a high gain at said resonant frequency for amplifying said resonant frequency output signal and warning means operated by said amplified output signal.

Claim 3

A device as claimed in claim 1, wherein the amplifying means comprises a first stage including a feedback loop which consists of a parallel tuned circuit resonant at the resonant frequency output from the piezoelectric element and a second stage driven from the first stage and whose output is applied through a high impedance path to the input of the first stage.

Claim 4

A device as claimed in claim 1, wherein the amplifying means comprises an operational amplifier feeding a bridge-T network employed as a feedback circuit to give the effect of a narrow band-pass circuit, and wherein the bridge-T network produces no feedback at a point on its characteristic which corresponds to the resonant frequency of the piezoelectric element and accordingly produces a sharp rise in gain of the amplifier at this point.

Claim 5

A device as claimed in claim 1, wherein the output from the amplifying means is applied through a demodulator to the input of a Schmitt trigger circuit producing an output pulse indicative of the duration of the contact or impact between said head and said disc and wherein the pulse from said Schmitt trigger circuit operates said warning means on the occurrence said contact or impact.

Claim 6

The combination of a plurality of magnetic discs mounted in a stack or pack and having a record or replay head associated with at least one side of each disc and an impact detector device associated with each of said heads and including a piezoelectric element having a resonant frequency mounted on each head for producing an electrical output signal at its resonant frequency when an impact occurs between that head and a disc, amplifying means having a high gain at said resonant frequency for amplifying the resonant frequency output signal from each piezoelectric device and warning means operated by said amplified output signal.

Claim 7

The combination of a plurality of magnetic discs mounted in a stack or pack and having a record or replay head associated with at least one side of each disc and an impact detector device associated with each of said heads and including a piezoelectric element having a resonant frequency mounted on each head for producing an electrical output signal at its resonant frequency when an impact occurs between that head and a disc, amplifying means having a high gain at said resonant frequency for amplifying the resonant frequency output signal from each piezoelectric device and warning means operated by said amplified output signal.