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 rock. Tom Schmitt tschmitt@.............. ----- Original Message ----- From: Robert W. AvakianTo: 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?? > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>