> I have a simular need, however mine is DC. Want to be able
> to measure up to 100A DC at 12V via a PIC

The frequency of the current to be measured determines
whether you'd use iron or ferrite in coils

You could start with a look at Allegro's UGN35xx linear devices

eg UGN3503

http://www.allegromicro.com/sf/3503/

http://www.allegromicro.com/datafile/3503.pdf  (183kB)

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Linear apps (includes measurement of 1000s of amps)

http://www.allegromicro.com/techpub2/an/an27702.pdf (143kB)

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The general apps pdf should give you enough background info

http://www.allegromicro.com/techpub2/an/an27701.pdf

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