The variability you are speaking of is sometimes called variable reluctance. Phillips (Ferroxcube) wrote a paper some years ago on the gluing of ferrite and how the constriction of the glue can change the reluctance of the core.
-Doug From: [email protected] [mailto:[email protected]] On Behalf Of Ralph McDiarmid Sent: Friday, October 06, 2006 9:33 AM To: [email protected] Subject: RE: Inductor mystery There is another documented effect, which I've also observed, wherein the permeability of the ferrite material changes with mechanical stress. That stress includes the tension of the copper wire winding. I recall that Siemens mentioned this effect in one of their old data books. Ralph McDiarmid, AScT Compliance Engineering Group Xantrex Technology Inc. From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Friday, October 06, 2006 8:09 AM To: [email protected]; [email protected] Subject: Re: Inductor mystery Since we are on the subject, let me toss in my two cents, even though I don't believe this to be the problem in this case. I have seen the characteristics of ferrite cores changed (apparently permanently) by passing a high current pulse though the inductor winding. This may seem like an unlikely situation until one thinks about a ferrite inductor on a power supply rail, and the rail then accidentally shorted to ground. The current pulse reduces the inductance substantially. Donald Borowski Schweitzer Engineering Labs Pullman, WA, USA Kbalasubramanian@ SCMMICRO.CO.IN Sent by: To [email protected] [email protected], [email protected] cc 10/06/2006 05:02 AM Subject Inductor mystery Dear Experts, We use the inductor part "1812CS-102XJLC" of Coilcraft in our RFID product as EMI filter. Continuously we face one issue, about 20 to 30 % products are functionally failing due to this inductor. While we change the inductor alone the product passes the functional tests. Hence we studied the characteristics of the inductor. Measurements carried out using the Agilent Impedance analyser 4294A shows the failing inductors and passing inductors are identical with respect to the below listed parameters for the entire measuring range of 40 Hz to 110 MHz. Our frequency of operation is 13.56 MHz and both the failing inductors and passing inductors are identical in this particular frequency also with respect to the below parameters. Is there anything else than the below listed parameters critical for an inductor? Has any one of you come across such an issue in your devices? I request your help. a. Ra.c b. Conductance - 'G' c. Reactance - 'X' d. Susceptance - 'B' e. Impedance - 'Z' f. Phase angle of the impedance g. Value of R, L & C measured using the equivalent circuit method of measurement. Sincerely K.Balasubramanian Project Leader - Hardware. This e-mail may contain SEL confidential or legally privileged 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 printed copies. - 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. 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