Scott,
Being a low frequency problem, it sounds like a likely candidate for a
common impedance coupling. Possibily through a common ground return. Mind
you, if it is Low freq in nature, series inductance [even large amounts ~ 3
mH ect...] and common-mode chokes may not work. Try checking the
grounding. The design should be such that no currents flows in any part of
the metal work, (which is a rather tall order for an automotive part).
:-)
Tim Foo
scott....@jci.com
Sent by: To:
emc-p...@majordomo.ieee.org
owner-emc-pstc@majordom cc: (bcc: Wan Juang
Foo/ece/staff/npnet)
o.ieee.org Subject: Low Frequency
Conducted Immunity....
11/02/01 09:04 PM
Please respond to
Scott.Mee
Thank you to all who have responded to my LFC immunity issue. Your help is
much appreciated.
Regards,
Scott Mee
EMC Engineer
Johnson Controls Inc.
PH: 616.394.2565
EMAIL: scott....@jci.com
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
Cortland Richmond <72146....@compuserve.com>
Sent by: owner-emc-p...@majordomo.ieee.org
10/31/01 12:50 AM
Please respond to Cortland Richmond
I'd be inclined to look at the design. Bandaids have a way of multiplying
until your product looks like a mummy.
If it's a low-level power problem, make sure the EUT's regulator can
respond to induced ripple. This may be as simple as exchanging a cheap
electrolytic cap for one with better ESR, or you may have to redesign the
regulator's filter loop.
If the problem is unregulated power to a PA stage, try getting better
balance in the stage; look at it as a CMR problem.
Look for ground-loop problems; a shared return between a stage run from the
injection point and a low-level amplifier will do what you report. And you
might look for an unintended path. Active switches can be modulated, too.
Good luck!
Cortland
"Ken Javor" <ken.ja...@emccompliance.com>
Sent by: owner-emc-p...@majordomo.ieee.org
10/30/01 02:54 AM
Please respond to "Ken Javor"
More info needed on type of power supply or whether unit simply runs off 12
Vdc. A power converter will definitely do the trick, but obviously is not
a solution unless it is already part of the EUT.
----------
scott....@jci.com
Sent by: owner-emc-p...@majordomo.ieee.org
10/30/01 12:42 AM
Please respond to Scott.Mee
Hello Group,
I am working with and electronic device which contains and audio output.
During a low frequency conducted immunity test, a tone can be heard at the
output of the audio section with a frequency equal to that of the test
frequency. The test starts at the lower end of the audio spectrum [~400Hz]
and progresses over time up to the top end of the audio spectrum [~30kHz].
I would like to be able to filter the conducted noise from getting into my
electronic device. This is an automotive application, so if I am
unsuccessful alternator noise may also be heard in my audio signal during
normal operation in the vehicle.
I have tried a few things to reduce the amount of noise such as:
1. LC filter with a cutoff at 1kHz
2. Series inductance [large amounts ~ 3mH]
3. Various common mode choke types, each with different core
materials [ie. iron core, ferrite core, etc....]
#1 helped some, but is not effective enough, #2 was very successful, but
the size of the choke would be enormous and not practical in this
application, #3 was not effective
Can anyone suggest an improvement upon the three methods above, or suggest
something different?
I would like to implement something on the board itself if possible, but
modification to the harness may be possible if necessary.
Thank you in advance for any help!
Regards,
Scott Mee
EMC Engineer
Johnson Controls Inc.
PH: 616.394.2565
EMAIL: scott....@jci.com
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