Magnetic Field Testing: DC: In the DC range compared to the Earth's magnetic field in the US your limit is about 12 times the earth's field. And, 6 times in some areas on earth. Seems a bit marginal. A pocket magnet could easily take you over this level. But most people know not to put magnets near a HD.
TO 700kHz: >From my experience with magnetic fields in the mid-range the limit seems to be a bit low: 7 milligauss seems a bit marginal for actual conditions. For example in our office/Lab the ambient field in the band "TO 700KHz" is around 300nT (3mG) [mostly from the AC mains. Lately, more is coming from those energy efficient fluorescent light sources with electronic ballasts operating at 30+KHz]. If I use the Boston Electric pencil sharpener sitting on the desk, the level often goes above this value. The sharpener is more than a meter away from the tower containing the Hard Drive, and when operating the sharpener, the field [at the HD] skyrockets to over 10-20 uT [100-200 mG]. According to your spec, that translates to having the HD getting 'upset' everytime I sharpen a pencil? That seems an unacceptible constraint to me. 700 kHz to 1.5 MHz: In the upper range band above 700KHz, one way to get 3m is by being near an AM Radio transmitting tower and in more than 90V/m field [easily coming from a 100KW transmitter]. I know this is all 'near' field, but taking some liberties: 90/377 = 0.24 A/m 0.24 * 4pi*10-7 = 3 nT [3mG] At those frequencies, it's unlikely to get that much field, even from magnetic deflection of a nearby old monitor. Advantageously, above 700KHz, the field is easily shorted by conductive plating, even 3 mil copper tape blocks well above 10KHz. Therefore, I don't understand why the susceptibility level is so low in this band. Or is the problem caused by the open areas of the bus communication? So my comments are: DC is marginal mid-range is too low hi-range is adequate Robert On Wed, 4 Jul 2007 17:31:57 +0900 "Kim Young-sik" <[email protected]> wrote: > Hi. all > > > > Regarding the contents lower part it knows and cotton > reply entrusting it gives. > > > Thank you > > > > ================================================================ > > 3.15 Magnetic Field > > > > The drive complies with the following > standards: > > > > FCC part 15 class B (USA) > > IC class B (CANADA) > > 89/336/EEC (EUROPE) > > > > The drive will meet its specified > performance while operating in the presence of an > externally produced magnetic field under the following > conditions: > > > > DC : > 6 gauss > > TO 700 kHz : > 7 milligauss maximum > > 700 kHz to 1.5 MHz : > 3 milligauss maximum > > ================================================================ - 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 ______________________________________________________________________
