On Tue, 27 Mar 2007 09:36:38 -0500, dgsvetan@rockwellcollins.com
wrote:
>As the LG design seems to show, the "hash" can be reduced to
>acceptable levels if the correct engineering and production
>techniques and materials are used.
Yes. We occasionally run into big problems with VFD's in pro audio
installations, where they are used for elevators, HVAC systems, and
geothermal systems. Like most other RFI issues, There, the problem
occurs when the designer or installer sets up a large loop area for
the RF components of the motor current by putting the power source
(stepdown transformer and controller) in one place and the motor in
another. Stray and bypass capacitance to ground in the motor carries
current in the large loop back to the ground of the transformer
and/or the controller, so you've got a big and nasty magnetic field
at LF, becoming EM at MF and HF.
As any good EMC engineer knows, RFI problems can be minimized by such
time honored techniques as minimizing loop areas, controlling rise
times, and suitable shielding.
Thanks to all who have named names. It makes it easier for us to be
educated consumers.
73,
Jim Brown K9YC
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