Our magnetics guru had the answer. The ground reference plane forms a mirror
image of the loop. Instead of the field increasing as the bottom conductor
is approached, the image forces the field to be uniform right down to the
plane. This is actually shown in Figures D7 and D8. Note that it is not
required that the loop be electrically connected to the plane for this
theory to work. The conductor could be spaced by a thin insulator. In fact,
this is what would happen with a multi-turn loop. In this case, the field
would not be exactly uniform very near the plane, so that is why the 0.1 m
spacer is used. However, in the end, I think Clause 7.2 and 7.4 are in
conflict and that 7.4 is correct. That is, any spacer of at least 0.1 m may
be used.
Richard Woods
----------
From: WOODS, RICHARD
Sent: Wednesday, January 17, 2001 12:25 PM
To: 'emc-pstc'
Subject: Annother EN61000-4-8 Issue
I believe that Clause 7.2 contains an error.
Clause 6.2.1 requires the field variation be no more than +/- 3 dB over the
volume of the EUT. For a 1 m square loop, the test volume is 0.6 m x 0.6 m x
0.5 m (h) with the loop centered on the test volume. Therefore, a vertically
oriented loop would be spaced at least 0.2 m above and below an EUT that
would fit within the test volume.
However, the first paragraph in Clause 7.2 requires that the equipment be
raised 0.1 m above the ground reference plain. - no more and no less. But,
the third paragraph of Clause 7.4 says that 0.1 m is the minimum distance.
It appears that Clause 7.2 is in error and Clause 7.4 is correct (it to is
wrong for a 1 m loop, but would be correct for a 0.5 m and smaller loop).
Comments?
Richard Woods
-------------------------------------------
This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
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:
Jim Bacher: jim_bac...@mail.monarch.com
Michael Garretson: pstc_ad...@garretson.org
For policy questions, send mail to:
Richard Nute: ri...@ieee.org
