Subject:  PC laptop with low EMFs (fwd)
Date:     Thu, 14 May 1998 092053 -0500 (CDT)
From:     "Roy L. Beavers" <rbeavers@llion.org>
To:       emfguru@hotmail.com
--------------------------------------------------


---------- Forwarded message ----------
Date: Thu, 14 May 1998 17:07:20 +0400 (EET DST)
From: Haldun Ozaktas 
To: "Roy L. Beavers" 
Cc: haldun ozaktas ,
    haldun ozaktas , aphilips@gn.apc.org
Subject: PC laptop with low EMFs


Most newer laptops have advanced liquid crystal (LCD) screens.

LCDs draw little current, so the magnetic fields are quite low. 
Also, they require low voltages, so the electric field can be low.
However, the backlighting may emit strong electric fields.
And also, as Alasdair mentions, there is the floating problem.

Gas plasma screens, which are less common, have low magnetic
fields as well. I measured about 0.1 milliGauss in front of
my Toshiba gas plasma. However, higher voltages are required
so these may have higher electric fields. James Schultz had
spoken of 10 kilovolts over the keyboard!!

Thus, both may have high electric fields but low magnetic fields.
Since electric fields can be shielded off, that looks ideal.

But...

(1) A laptop forces you to be close to it. My 17 inch TCO'95 monitor
is almost a meter away from me. Thus, the low frequency ELF band
fields you get from a laptop will not be 1000's of time less,
although still quite small.
For a permanent desk top, one can get a large (size and $$$)
stand-alone LCD and put it far away and screen it with a grounded screen.
That arrangement will be good but may not improve significantly
over a TCO'95 monitor used in the same manner.

(2) Laptops and their TFT screens may give off much more high-frequency
(higher than ELF and VLF) compared to ordinary monitors.
Not covered by TCO and can't measure with ELF meters.

(3) My Toshiba has a separate power supply with a grounded three-wire
cord to the mains. But, the cord connecting it to the computer is 
two-wire. Are you saying it is sufficient to determine the ground
pin of either the serial or parallel port and tie a wire from
here to the ground at the wall plug? I was tempted to tie a wire
from some metal part of the computer to the ground of the plug,
but I wasn't sure it was safe and what exactly the result would be.
Any authoritative claim on this?
(Yes, I am in an electrical engineering department but yes I
am not confident with practical electronics and so forth.)

I am also surprised an extra grounding screen does not further help.
That means it is the float problem and only the float problem.
I would have thought even with grounding the backlit screen emits
electric fields.

Haldun

________________________________________________________________________
Haldun M. Ozaktas
Bilkent University                      (90) (312) 266 40 00 / 1619
Department of Electrical Engineering    (90) (312) 266 43 07 (secretary)
TR-06533 Bilkent, Ankara, Turkey        (90) (312) 266 41 26 (fax)
www.ee.bilkent.edu.tr/~haldun           haldun@ee.bilkent.edu.tr


> ---------- Forwarded message ----------
> Date: Wed, 13 May 1998 08:44:27
> From: Alasdair Philips 
> 
> Most modern lap-tops give off negligible EMFs (1000's of times less than
> even the best desk-top VDU units) BUT....
> Most, when run from their mains-adapters/re-chargers float up to half the
> supply voltage (i.e. about 60vAC in your case, 120vAC in most of Europe)
> which causes the keyboards to give off VERY high EMFs of several hundreds
> of volts per metre.
> 
> The cure is easy ~ you need an earth wire from the computer (usually connect
> at one of the port connectors on the rear) to a local safety electrical
> earth line (usually available at the mains plug).  The reason for this
> problem is that most laptop psu's only have a two wire connection to the
> mains and therefore "float" (it is called "double insulated") ~ which is
> a real problem for ES and can also cause/aggravate RSI as the fingers are
> in these high electric fields.
> 
> I have not found the use of a screen helps reduce EMFs in laptops if the
> above "earthing" is done, and they increase eye strain as the displays 
> are never super-bright to start with.
> 
> Alasdair Philips,
> EMF Consultant, UK.




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Reprinted with permission of Roy Beavers, http://www.feb.se/EMF-L/EMF-L.html