ChrisAtUpw@....... wrote:

> Dear Meredith,
>     I use a Mu-Metal cylinder 3.5" dia by 8" long  by 0.020" thick and it
> gives a measured axial field reduction of about x30 at the centre. In the
> Earth's field, I can't measure any transverse field effect. When you bend
> Mu-Metal, the permeability does decrease a bit.
>     Regards,
>     Chris Chapman

Hi Chris,

Thanks for the info on the field reduction of your unit, it helps
give me an appreciation of the effect of shielding thats possible.

Of course, a Hall sensor can be made into a gauss meter, or,
is the main part for such, which you likely used there.

Its also possible to see some reduction effect, by using Robert Lambs
Hall sensor circuit, and open and close (the) potential shield
over it.  He had a small ~ 4"L x 1.5" diameter open mu-metal
cylinder that he shoved the Hall sensor in as a demonstration
.....it roughly halved the circuit noise at that time.  Of course this
just reminds me that a similar shield around the S-G type Hall
circuit seismos could also be beneficial in that aspect.....but;
for that application, the shield could be alot smaller and
close to the Hall sensor itself.  Thats another undone project
......ha.

Take care,

Meredith Lamb





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