I have done a similar project but I had to design the whole sensor thing by
myself. I designed a toroid with proper parameters and using a 16f84a I
could print the current in the wire to lcd.

My investigations have revealed that the
> B-field ( magnetic field ) around a wire is
> approximately B =3D ( N I =B5 )/L .
> N =3D number of turns which in this case is one.
> I =3D current which for my purposes is a
> minimum of one amp.
> =B5 =3D permeability which is ~ [10
> minus 6] for copper or aluminium.
> I am guessing that L is .005 for a
> wire one cm in diameter.
>

almost complete except that you need to calculate the phase difference
caused from the impedance mismatch of your materials. This was also a
parameter at my project but if you use a fabricated sensor this may vary.

>
> Using those values I get a B field of
> [2 x ten minus 4 ] Tesla or 2 Gauss.
>
> If I did the calculations correctly, it seems
> that an Allegro A1323 linear hall effect sensor
> ( HES ) (1) should work.  This part has an output of
> 2.5 mv / G.  I am planning to measure a range
> of 1 amp to 200 amps.  Should I make the
> HES part of a magnetic ring around the
> wire ? The ring would consist of two "C" sections
> married to each other sandwiching the HES.
> Would steel be a suitable material
> given I am measuring DC to 120 Hz ?  Does the
> steel have to be laminated ?  Or would a ferrite
> ring be necessary ?


you can't measure DC since it will not induce a magnetic field. Also notice
that you need to have very precise equipment in order to get accurate
results at VLF.


> After single point calibration , I would like to
> see an accuracy of .1% .
>

totaly achievable, excluding EMI of course.

I can send you complete report of my project, drop me an email.
-- =

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