[SI-LIST] commom-mode current limit on hard disks

Hello si-list,


I have a question concerning hard disk immunity with respect to common-mode
(CM)
currents on it's cables, that is, what is the maximum limit (very likely
frequency dependent)
of CM currents on the power port and/or data cable.

The CM currents are due to parasitic capacitive (or possible conductive)
coupling between
the hard disk and the chassis. The parasitic CM currents interfere with the
disk operation
during read/write operations, which use sensitive analog signals and are,
as such, prone
to intereference from these stray currents.

I have seen specifications of CM current limits of amplitude versus
frequency.

In the past I have had a good repsonse from IBM people on this list. I was
hoping that
they or others could contribute some information on this topic.

Kind regards,

Jan Vercammen
EMC/SI Engineering
Agfa-Gevaert NV, Belgium

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