FW: [SI-LIST] : EMC at low frequencies

Johnson, David (david.johnson@intel.com)
Wed, 26 May 1999 16:07:05 -0700

Effects of 50Hz/60Hz magnetic fields on CRT display monitors was a subject
of attention at the Video Electronics Standards Association (VESA) late last
year. VESA's work was prompted by power industry responses to user
complaints, in an effort to better educate end users about CRT display
monitors. The result was a brief list of seven remedies that an end user
can experiment with to reduce or eliminate visible interference (nothing
quantitative; no engineering-level spec's or experimental data). The
document is titled, "Guideline to Reduce the Visible Effect of Magnetic
Interference on Computer CRT Displays."

Although the VESA document is only 11 KB in size ("pdf" file) and only a
little over one page when printed, it is under VESA copyright (10/14/98) and
isn't necessarily available to non-members without payment of a modest fee
to VESA. The location of the document is as follows on the VESA "private
FTP site" (password protected; contact VESA for access):
committees/standard/emc.pdf (file date 11/3/98). The VESA organization can
be reached at http://www.vesa.org.

Other standards bodies may, perhaps, have more extensive standards for
quantitatively specifying various controlled test conditions for
low-frequency electric and magnetic fields.

---- Dave W Johnson, Intel

-----Original Message-----
From: Adrian Shiner [mailto:adrian.shiner@virgin.net]
Sent: Wednesday, May 26, 1999 2:59 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : EMC at low frequencies

EMC effects start at effectively 0Hz. Many non industrial computers
(office type computers) and communications equipment will not "safely
shut down or recover to a safe mode" in the event of a predictable
electrical mains supply disturbance. It is extremely (almost impossible)
to obtain data on immunity to power supply disturbances for this type of
equipment. A failure of one computer due to being placed close to a
400Hz inverter (stray magnetic fields) prompted the question " What is
the immunity to magnetic fields?". "We don't know" was the response
from a major computer manufacturer.

Without compromising commercial positions, can anybody provide some
light work going on to improve this situation? Continuing with the
common approach of "Hard luck friend, see the escape clauses in our
conditions of sale" is not likely to improve the performance of the
Information Technology business.

Adrian

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