PSN-L Email List Message

Subject: Re: Mu-Metal???
From: "Tom Schmitt" tschmitt@..............
Date: Sun, 18 Jun 2000 22:32:21 -0400

I have been on vacation so this is a late post.

The coils on the spinner magnetometer were oriented in a Helmholtz geometry.
They are designed to produce a
uniform magnetic field parallel to the axis of the two coils.  On the older
spinner magnetometers there was a
single set of Helmoltz coils oriented vertically to cancel out the vertical
component of the earths magetic field.

The fluxgate magnetometers were oriented vertically also.  This arrangement
of the coils and the magnetometers
allowed the flux gate to measure teh remenant rather tha the induced
magnetism of the rock.  The spinning was done
for signal processing.   They usually spun at 40 Hz or so and the amplifier
was tuned to that frequency.

Later magneometers used a mu metal shield for the same reason, to have the
flux gates measuring the rremenant magnetization not the induced.

Much later cyrogenic magnetometers used super-conducting shields to isolate
the sample from the earths and
other ambient fields and used SQUIDS to measure the magnetzation of the

Tom Schmitt


----- Original Message -----
From: Robert W. Avakian 
Sent: Wednesday, June 14, 2000 1:10 AM
Subject: Re: Mu-Metal???

> The setup used to isolate our spinner magnetometer from Earth's field at
> a college I attended was simply an openwork frame with copper wire
> wrapped around it, and not much of that.  It was attached to a DC power
> supply which in turn was plugged into the wall.
> Does anyone know what amount of shielding a spinner magnetometer, (used
> to make paleomagnetic measurements on small orck cores), needs compared
> to this use??
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Larry Cochrane <cochrane@..............>