Subject: EEG and RFI/EMF

From: [email-masked] (Lawrence O. Lile)
Date: 13 May 1995 02:48:52 -0400

I am designing an EEG suite for a neurologist at a hospital.  He is
very concerned about interference from fluorescent lights, VDTs, etc.
which can ruin a sensitive EEG test.  He recommends shielding
the entire room with copper mesh.  Has anyone done lighting design
for a similar EMF sensitive application?  What kind of lights did you
use?  What shielding materials work well?

Lawrence Lile, P.E.
Electrical Engineer
[email-masked]

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From: [email-masked] (John MacDonald)
Date: 26 May 1995 10:51:55 -0300

>[email-masked]
Lawrence,  I believe that what this neurologist is concerned with is not
fluorescent lamps but electronics fluorescent ballasts.  Magnetic 
fluorescent ballast operate at 60Hz, but the electronic version operate
at anywhere from 25kHz (first generation) to 50kHz (newer versions).  This
can cause two problems.  The first is that the ballast itself can emit
RFI which can interfere with other electronics.  The second is that the 
lamp is strobing UV at high frequency.  This has recently been investigated
with the new higher frequency ballast as the UV emmisions from the lamp
have been known to interfere with devices such as IR garage openers, etc.
If he is concerned about VDTs, I would assume that the EEG equipment that 
he is using may be susceptible to lamp UV emmisions as well (you need to
check into this - it may not be a concern if the frequency of the ballast
and the equipment do not match).  If this is a problem, though, then 
shielding with copper will not likely help (with the UV problem - it may
with the RFI problem).  If electronic ballasts are a problem try reverting
to magnetic ballast.  The only problem with them is that flicker can be 
noticeable due to the fact that they are only strobing at 120 Hz (2xoperating
frequency).  Hope this helped.

John MacDonald
[email-masked]  
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From: [email-masked] (John MacDonald)
Date: 29 May 1995 12:24:51 -0300

>use?  What shielding materials work well?

Lawrence, I also just came across an article in Compliance Engineering 
magazine which deals with EMI concerns in medical environments.  It was 
in the March/April 1995 issue Page17 and was titled "Product-SAfety Requirements
for Medical Electrical Equipment. Enjoy!