In message <538ea5c5.6070...@emcesd.com>, dated Tue, 3 Jun 2014, Douglas
Smith <d...@emcesd.com> writes:
I just posted my latest Technical Tidbit a few hours ago using a class
D stereo amplifier to illustrate a potential problem whereby emission
test standards may understate the emissions from a digital device. Here
goes:
I wouldn't contest your results, but...
Abstract: Radiated emissions measurements of table top equipment are
usually made with the equipment placed on a non-conductive table.
This is because the standards committees are primarily concerned with
household products, used in very large numbers, unless they are
specifically considering professional products (as defined).
But such equipment is often used on conductive surfaces, like a metal
desk, and can couple to the conductive surface to enhance emissions,
essentially turning the conductive surface into part of an antenna
structure.
This is unlikely in the home but is much more likely in a commercial,
light industrial or industrial environment. There is a move to
reconsider how 'Class A or Class B' is working, but of course it is
controversial. Nevertheless, it could be very relevant in this context.
When this happens, standard testing of emissions can understate actual
emissions. A Class D (actually labeled Class Z) stereo amplifier is
used to illustrate this effect by measuring common mode current on its
cables.
I'm surprised that the maker stopped at Z: there's the whole Russian, or
even Georgian, alphabet to explore. (;-)
Link to the article: http://www.emcesd.com/tt2014/tt060114.htm
Link to the whole site: http://www.emcesd.com (lots of new stuff)
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Quid faciamus nisi sit?
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
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