Helmholtz coils produce a field of approx 'uniform' to 1% over a volume of one third your coil's volume. In other words, a coil 2 meters by 1 meter height produces a uniform field about 30 cm cube. Or, is that 60 by 30 ?? can't remember now, but easy to check. Do you have femm 4.2? do an axisymmetric model and can find out.
It's pretty easy to measure 20nT variation within 50uT background, you may not need a bias. Use two sensors and subtract the two signals like differential probes on a scope where you're removing the common mode. --- [email protected] wrote: From: S Drysdale <[email protected]> To: Macy <[email protected]> Subject: Re: [PSES] DC Magnetic emissions. Date: Sun, 25 May 2014 20:03:00 -0400 Hi Macy, Much appreciated. It does help, and we'll look at pricing and leadtime. I think my main problem is going to be how to deal with the ambient environment and how to properly use helmholtz to cancel the field. Best Regards, Scott Drysdale OOO - Own Opinions Only On Sun, May 25, 2014 at 9:08 AM, Macy <[email protected]> wrote: > try these people. They make a 12 digit magnetic field meter, YES 12 digits! > > earth's field approx 50uT, > > > Geometrics has been a world leader in the design and manufacture of > geophysical instrumentation since 1968. > http://www.geometrics.com > > Geometrics 408 954 0522 > 2190 Fortune Drive fax 408 954 0902 > San Jose, CA 95131 > > > --- [email protected] wrote: > > From: S Drysdale <[email protected]> > To: [email protected] > Subject: [PSES] DC Magnetic emissions. > Date: Sat, 24 May 2014 21:28:18 -0400 > > Good day all, > > Is anyone here familiar with very sensitive DC magnetic emissions? I am > particularly interested in performing measurements in the low mG range, > well below the value of the earths magnetic field. I believe a 3 axis > helmholtz coil for earth field compensation and a sensitive DC milligauss > meter will be required. Any specifications, methods, guidance documents, > equipment recommendations, or general advice would be greatly appreciated. > > Best Regards, > Scott Drysdale > OOO - Own Opinions Only > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
