Monitoring a fly height of a magnetic transducer

1. A method for monitoring a fly height of a magnetic transducer, said method comprising:

flying said magnetic transducer at a distance of separation from a recording media;

modulating said fly height with a predetermined modulation frequency with a fly height control device;

reading a read-back signal from said recording media with said magnetic transducer;

measuring a change of said read back signal resulting from said modulating said fly height, wherein said measuring a change of said read back signal comprises:

splitting said read-back signal into a first branch and a second branch;

multiplying said first branch by said predetermined modulation frequency, resulting in a first multiplied signal;

multiplying said second branch by a synchronous clock quadrature of said second branch, resulting in a second multiplied signal; and

filtering said first multiplied signal and said second multiplied signal; and

providing a fault signal in response to said change crossing a threshold.

2. The method of claim 1 wherein said flying said magnetic transducer comprises:

flying a slider having a thermal fly height control device.

3. The method of claim 1 wherein said flying said magnetic transducer comprises:

flying a slider coupled with a hard disk drive.

4. The method of claim 1 further comprising:

demodulating said read-back signal.

5. The method of claim 1 wherein said measuring a change of said read back signal comprises:

a phase lock loop.

6. The method of claim 1 wherein said measuring a change of said read back signal comprises:

measuring an amplitude of at least one of said first multiplied signal and of said second multiplied signal.

7. The method of claim 1 wherein said measuring a change of said read back signal comprises:

measuring a phase having said first multiplied signal and said second multiplied signal.

8. The method of claim 1 wherein said filtering said first multiplied signal and said second multiplied signal comprises:

setting a fly height detection bandwidth.

9. An electronics module operable for receiving a read-back signal from a magnetic transducer, said electronics module comprising:

a modulation generator operable for receiving a predetermined modulation frequency and operable for providing a modulation clock signal for a fly height control device;

a measuring circuit operable for measuring a change in said read-back signal, wherein said change is in response to altering a fly height in response to said modulation clock signal received by said fly height control device, wherein said measuring circuit further comprising:

a splitter operable for splitting said read-back signal into a first branch and a second branch;

a first multiplier operable for multiplying said first branch by said modulation clock signal effecting a fly height modulation;

a modulation processor operable for presenting to said measuring circuit a fly height amplitude from said fly height modulation; and

a filter operable for passing a at least one mechanical frequency of said magnetic transducer; and

a threshold detector operable for providing a fault signal coupled with a threshold of said change in said read-back signal.

10. The electronics module of claim 9 wherein said modulation generator further operable:

for providing a modulation clock quadrature signal to said modulation processor.

11. The electronics module of claim 9 wherein said measuring circuit further operable:

for measuring a change in resistance of a magnetic transducer.

12. The electronics module of claim 9 wherein said threshold detector is coupled with an output port.

13. The electronics module of claim 9 wherein said threshold detector comprises an RMS threshold detector.

14. The electronics module of claim 9 further comprising:

a second multiplier operable for multiplying a second branch by a modulation clock quadrature signal resulting in a fly height modulation quadrature; and

a modulation processor operable for presenting a fly height modulation phase from a fly height modulation quadrature.

15. The electronics module of claim 9 further comprising:

a full wave rectifier for demodulating said read-back signal.

16. The electronics module of claim 9 further comprising:

a half wave rectifier for demodulating said read-back signal.

17. A hard disk drive comprising:

a base casting for providing attachment points for major components of said hard disk drive;

a motor-hub assembly to which at least one disk is coupled, wherein said motor-hub assembly is attached to said base casting, wherein said disk has at least one surface of data tracks;

a head stack assembly comprising:

a comb to which at least one suspension is coupled, wherewith a slider including a magnetic transducer for reading and writing said data tracks onto said surface is coupled with said comb;

an arm electronics module operable for receiving a read-back signal from said magnetic transducer, said arm electronics module comprising:

a modulation generator operable for receiving a predetermined modulation frequency and operable for providing a modulation clock signal for a fly height control device;

a measuring circuit operable for measuring a change in said read-back signal, wherein said change is in response to altering a fly height in response to said modulation clock signal received by said fly height control device, wherein said measuring circuit further comprising:

a splitter operable for splitting said read-back signal into a first branch and a second branch;

a first multiplier operable for multiplying said first branch by said modulation clock signal effecting a fly height modulation;

a modulation processor operable for presenting to said measuring circuit a fly height amplitude from said fly height modulation; and

a filter operable for passing a at least one mechanical frequency of said magnetic transducer; and

a threshold detector operable for providing a fault signal coupled with a threshold of said change in said read-back signal.

18. The hard disk drive of claim 17 wherein said arm electronic module comprises a filter operable for passing at least one mechanical frequency of said magnetic transducer.

19. The hard disk drive of claim 17 wherein said read-back signal from said magnetic transducer does not comprise data from said data tracks.

20. The hard disk drive of claim 17 wherein said threshold detector is coupled with a controller of said hard disk drive.

21. The hard disk drive of claim 20 wherein said controller, in response to said threshold detector providing said fault signal which exceeds said threshold, increases said fly height of said magnetic transducer.

22. The hard disk drive of claim 20 wherein said controller, in response to said threshold detector providing said fault signal which does not exceed said threshold, decreases said fly height of said magnetic transducer.

23. The hard disk drive of claim 20 wherein said controller, in response to said threshold detector providing said fault signal, stops at least one operation of said hard disk drive.