When I managed both EMC and power supply design groups in the '80's,
I found the many tech magazine ads for open frame power supplies quite
amusing. These always stated that the power supplies met FCC and other
EMI requirements. How were these tested? A dummy d.c. load does NOT
impose a particular challenge on a power supply. Real life loads are
dynamic in nature, and can significantly alter the total EMI measured.
>From my knowledge of EMI testing, it became apparant that changing
ANY part of a system that could conduct electrons could alter the EMI
profile. One basic "law" holds true for electrons in a system; viz.
they will always take the path of least resistance in getting from A
to B. However, the least resistive path changes with increasing
frequency. At the higher frequencies of interest, it is not unusual
for the electrons to be racing through the metal covers rather than
the intended paths.
The reason that CE + CE = CE is not typically true is that a
combination of units can produce EMI results that are:
A. better than the "sum" of the individual components
B. same as the individual components
C. worse than any of the individual components
Since global EMC requirements are based on the complete system as it
will be used (e.g. PC, monitor, keyboard, mouse, printer,...) it is
always best to test the complete system the the very components that
will be used.
George Alspaugh
-------------------------------------------
This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/
To cancel your subscription, send mail to:
majord...@ieee.org
with the single line:
unsubscribe emc-pstc
For help, send mail to the list administrators:
Michael Garretson: pstc_ad...@garretson.org
Dave Heald davehe...@mediaone.net
For policy questions, send mail to:
Richard Nute: ri...@ieee.org
Jim Bacher: j.bac...@ieee.org
All emc-pstc postings are archived and searchable on the web at:
http://www.rcic.com/ click on "Virtual Conference Hall,"
