I don't understand how a non-uniform illumination would cause more susceptibility than uniform illumination. While I agree that non=-uniform is more likely, I have always assumed you want uniformity for repeatability and to make it worst-case.
> From: "Robert A. Macy" <[email protected]> > Date: Wed, 04 Jul 2007 11:39:58 -0700 > To: Ken Javor <[email protected]> > Cc: [email protected] > Subject: Re: Please reply to me (Magnetic Field testing ) > > 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 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 ______________________________________________________________________
