Soft Ferrites cannot be permanently magnetized. This is precisely why they are used as beads and cores.
Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: Robert Macy [mailto:m...@california.com] Sent: June 5, 2002 11:20 PM To: don_borow...@selinc.com; emc-p...@majordomo.ieee.org Cc: shbe...@rockwellcollins.com Subject: Re: ferrite transient voltage/current response He may have magnetized it. Degaussing with one of those Radio Shack thingies would probably brought it back. Can he try it again? - Robert - Robert A. Macy, PE m...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -----Original Message----- From: don_borow...@selinc.com <don_borow...@selinc.com> To: emc-p...@majordomo.ieee.org <emc-p...@majordomo.ieee.org> Cc: shbe...@rockwellcollins.com <shbe...@rockwellcollins.com> List-Post: emc-pstc@listserv.ieee.org Date: Wednesday, June 05, 2002 2:52 PM Subject: RE: ferrite transient voltage/current response > > > >While I was at Agilent in Spokane, one of the engineers or technicians claimed >that he had changed the RF characteristics of a 6-hole ferrite bead (wound with >2 1/2 turns) used on a power supply trace to a noisy assembly. The normal >current was about 1 amp, but he accidently shorted the power supply voltage >after the inductor. This caused a current spike as the power supply filter >capacitor discharged (and then the supply current limited at about 10 amps). >After this, there was a problem with RF leakage from the assembly. Replacing the >inductor fixed the problem. Apparently the effect was repeatable. > >I didn't observe this personally, so I can't guarantee it. > >Don Borowski >Schweitzer Engineering Labs > > >Sorry that I wasn't clear; I typically try to keep my questions general so > not to get too detailed about the specific application. And thanks to Bob, > Chris and Mike who have responded ... putting it into Chris's words ... I > was just trying to find out if ferrites had ratings to prevent them from > "j > ust plain blowing the ferrite to smithereens". Also, I was looking for a > shortcut if someone else had faced this question rather than reading > through all of the vendor web sites. > > I understand and have used ferrites quite often for typical EMI >suppression; the ferrites typically being rated for the application >currents, voltages, etc. In this case, the program is trying to protect a >power supply input from the DO-160 waveform 5B pin injected lightning pulse >of 300 volts open circuit & 300A short circuit. If the Gas Discharge Tube >is located past (closer to the supply which was done for packaging >limitations) than the "T" EMI filter, a question was raised as to whether >the ferrite properties would be altered by the lightning pulse. Most of >the standard literature on the use of ferrites does not address these types >of transients. > > >Susan Beard > > > > > > > >"Robert Wilson" <robert_wil...@tirsys.com>@majordomo.ieee.org on 06/04/2002 >02:16:48 PM > >Please respond to "Robert Wilson" <robert_wil...@tirsys.com> > >Sent by: owner-emc-p...@majordomo.ieee.org > > >To: <shbe...@rockwellcollins.com>, <emc-p...@ieee.org> >cc: > >Subject: RE: ferrite transient voltage/current response > > > >Your question is not all that clear. It appears to imply that transients >have an affect on the ferrite beads, but it is the other way around >(maybe that is what you meant). But in general, small ferrite beads have >little effect, except at very high frequencies (hundreds of MHz), unless >they are no longer "beads" (i.e. they are very large). > >Have a look at the various magnetics vendors data sheets and app notes. > >Magnetics Inc: www.mag-inc.com >Fair-Rite Inc: www.fair-rite.com (whoever came up with THAT name should >be shot! >Steward Inc: www.steward.com >Ferroxcube: www.ferroxcube.com >Epcos (was Siemens): www.epcos.com > > >Bob Wilson >TIR Systems Ltd. >Vancouver. > >-----Original Message----- >From: shbe...@rockwellcollins.com [mailto:shbe...@rockwellcollins.com] >Sent: June 4, 2002 8:57 AM >To: emc-p...@ieee.org >Subject: ferrite transient voltage/current response > > >Could someone point me to some good App Note information on the response >of >and affect on ferrite beads to transient voltage & current waveforms? >The >waveforms are based on the indirect lightning pulses specified in >Section >22 of DO-160. > >Thanks in advance, >Susan Beard > > >This e-mail may contain SEL confidential information. The opinions expressed >are not necessarily those of SEL. Any unauthorized disclosure, distribution or >other use is prohibited. If you received this e-mail in error, please notify >the sender, permanently delete it, and destroy any printout. Thank you. > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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