Sometimes, gradients generated by a dipole can aggravate a weak design better than nice uniform fields. Especially if there aren't enough "twists per inch" on the PCB layout.
And, probably more represent an interfering source. Few noise sources produce uniform fields. Robert On Wed, 04 Jul 2007 13:28:06 -0500 Ken Javor <[email protected]> wrote: > That is indeed the case. The coil diameter, the number of > windings, the wire > gauge and the distance between the plane of the XMIT loop > and the surface of > the test article are all specified, resulting in a > well-controlled test. > > An aspect that is well-controlled but perhaps not > optimized is the > orientation of the magnetic field relative to the > circuits within the test > article. The field orientation is determined by the > topology of the test > article enclosure, so the test will be performed the same > at every test > facility, but the orientation of the magnetic field lines > relative to the > plane of any victim circuit loop will be determined by > the layout within the > enclosure, and there is no guarantee that the test field > is cutting the > victim circuit plane(s) at right angles. Therefore it is > not assured that > meeting the test requirement demonstrates compatibility > with a real world > source of even the same magnetic field intensity. From > this point of view, > a Helmholtz coil of dimensions large enough to rotate the > test article > within would seem a better choice, but these are hard to > drive to desired > field intensities at frequencies that now extend to 100 > kHz, and even at the > beginning extended to 30 kHz. It may be we need a > Helmholtz coil approach > for dc, the power frequency and maybe the first ten > harmonics, and if a > requirement extends above that, you use the small loop - > the original > military driver for this requirement was protection of a > VLF receiver, not > power frequency compatibility. > > > From: John Woodgate <[email protected]> > > Date: Wed, 4 Jul 2007 18:43:13 +0100 > > To: [email protected] > > Subject: Re: Please reply to me (Magnetic Field testing > ) > > > > In message > <c2b141c4.58eb8%[email protected]>, dated Wed, > 4 > > Jul 2007, Ken Javor <[email protected]> > writes: > > > >> I don't know what the commercial standards require, > but for instance > >> MIL-STD-461 has the field intensity (Tesla) limit > augmented by a > >> precise description of the coil diameter to be used > when generating the > >> field. This completes the requirement and makes it > repeatable across > >> test facilities. > > > > I think the distance of the coil from the surface of > the product is also > > specified, isn't it? That determines, in practical > terms, the field > > pattern of an inhomogeneous field, which is very > difficult to define > > otherwise. > > -- > > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and > www.isce.org.uk > > There are benefits from being irrational - just ask the > square root of 2. > > John Woodgate, J M Woodgate and Associates, Rayleigh, > Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
