Happy Holidays everyone,
In the test labs I've worked in we had a hard and fast rule. If you couldn't
document what ferrite it was that you had in your hand it wasn't used. I
always had to write up the modification documentation to accompany the report
and data and I knew I didn't want to guess about what part was used.
Just my $0.02......
Michael Sundstrom
NOKIA
TCC Dallas / EMC
ofc: (972) 374-1462
cell: (817) 917-5021
amateur call: KB5UKT
From: owner-emc-p...@majordomo.ieee.org
[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of ext Price, Ed
Sent: 19 December, 2003 09:10
To: emc-p...@majordomo.ieee.org
Subject: RE: Measuring a ferrite performance
-----Original Message-----
From: Chris Maxwell [ mailto:chris.maxw...@nettest.com]
Sent: Friday, December 19, 2003 6:29 AM
To: Ken Javor; Price, Ed; Grasso, Charles; emc-p...@majordomo.ieee.org
Subject: RE: Measuring a ferrite performance
As usual, this thread has been very educational, the mere asking of the
question has unleashed many answers, from which I have gained in my own
knowledge. The most practical question that I would ask is:
Why the h___ would your component engineering group want you to measure the
impedance of a ferrite? There can only be two reasons: either they can't
get a graph of impedance from the manufacturer, or they don't trust it. If
either of these are true; then I wouldn't buy the ferrite in the first place.
I hope that this isn't a "slippery slope" issue for you. Otherwise, your
component engineering group may be asking for V-I curves whenever you want to
qualify a new resistor J.
All that said, I can appreciate the fact that you may want to perform this
measurement just to learn how it's done.
If you do perform the measurement, I would recommend one little detail. I
would recommend that you first find a "known good" ferrite complete with a
manufacturer's impedance graph. Compare your measurements to the graph just
as a sanity check.
Happy holidays
Chris Maxwell
Design Engineer
Nettest Inc.
Utica, NY
chris.maxw...@nettest.com
Chris:
I don't know how other labs manage their test aids, but I'm afraid that I have
to admit that ferrite beads and clamps are a poorly controlled commodity in my
lab. Despite the best efforts of the good salesmen from Steward & Fair-rite &
others to keep me stocked with ferrite sample kits, I still am often faced
with a project engineer who brings his own supply of unidentified ferrite
goodies.
Given the scenario where we find some obnoxious high-order clock harmonics, or
some digital hash that's found an unlucky resonance, my customer's typical
response is to dig into his pockets and produce a few ferrite beads or tubes.
"Let's try mine first!" And if you get lucky, and the first fix works, they
are usually loath to spend more time in optimization. The usual response is
something like "OK, this definitely works; now what is it?"
I sure wish that ferrite manufacturers had a color-code system like you have
for resistors. Sure, some of those beads & chips are darn small, but I wonder
if even high-volume parts might be markable with some kind of laser-etched
bar-code. (Reading that bar code might be another challenge!) OTOH, even if,
starting tomorrow, all ferrites were marked, it would probably take longer
than my lifetime for the supply of unmarked stashes to be exhausted.
Regards,
Ed
Ed Price
ed.pr...@cubic.com WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
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