Re: [PCWorks] Stray EM fields, CRT's & effects Re: Burning CDs
- From: whckm@xxxxxxxx
- To: pcworks@xxxxxxxxxxxxx
- Date: Mon, 10 Nov 2008 08:18:12 -0500
The magnetic shield you are asking about is called mu metal.
(After the Greek letter "mu"). It has the ability to absorb
a large amount of a magnetic field before it saturates.
When it saturates, the excess magnetic fields will pass
right through it. The thicker the metal, the more of the
magnetic field it will shield. The beams in CRT's are
focused and directed by magnetic fields and the
mu metal shields are to protect the beams from distortion
by external magnetic fields.
Try bringing a magnet to the face
of a CRT and see what happens. The monitor also
has a large loop of wire around the face of the CRT
which carries a large pulse of current each time
the monitor is turned on. This is supposed to erase
any stray magnetization in the CRT that might
affect the quality of the picture.
The danger to the person sitting in front of the
monitor is from ionizing radiation. (X-rays)..
X-rays are created when high energy electrons
(created with a high voltage) strike an object like the
glass and color dots of the CRT. I think they solved
this problem by using X-ray absorbing glass and making
it thicker. Eventually with larger CRT's and higher
voltages in TV sets, they had to shield the back of the monitors
because X-rays scatter in all directions. Most metals
do a fair job of shielding low voltage X-rays.
(35,000 volts is considered low voltage generation.
Chest X-rays approach 150,000 volts).
Wally
On Sun, 09 Nov 2008 03:36:35 +0200 David Grossman <dgrossman@xxxxxxxxxx>
writes:
> I don't know what that material is, Peter, but I have no doubt that
> the
> industry will develop an artificial or synthetic replacement well
> before
> 2017.
>
> We may not even need monitors. I saw a keyboard replacement at an
> exhibition. A picture of the keyboard is projected onto your working
> area or
> table, and you can type on it directly. Similarly, the previews that
> I saw
> of Windows 7 show an onscreen touch keyboard that can replace the
> regular
> keyboard (although it must be very difficult to get any speed typing
> vertically!)
>
> Similarly, the industry can find a replacement for screens - either
> by
> projecting them onto the wall or a table or a working area. I don't
> think we
> should worry about the planet running out of materials to build
> LCDs.
>
> David Grossman
>
>
> > So crt's are being made less and less as lcd and plasma monitors
> gain
> > popularity so lesser need for shielding. As an aside, lcd's must
> evolve
> > as well as one important material in their construction will be
> > exhausted by 2017.
> >
> > A fellow student from a while back worked on concert stage
> construction
> > and shielded each and every speaker magnet with a sheet steel box.
> Must
> > have been a lot of boxes.
> >
> > Peter Kaulback
> >
> > Clint Hamilton-PCWorks Admin wrote:
> > >> By the way, I don't know whether Energy Star
> > >> has to do with radiation. It has to do with
> > >> electricity consumption.
> > >
> > > Yes, I'm not sure it does: "In the USA, all monitors now are
> > > 'Energy Star' compliant which also ***might*** reduce
> > > radiation". I guess if you make them more efficient that
> > > **might possibly** reduce some of the radiation.
> > >
> > > Again, I'm mostly talking about **magnetic** fields. A CRT
> > > doesn't really have enough to damage a flash drive or SS HD,
> > > unless perhaps it's resting on top for a period of time.
> > > Shielding of harmful magnetic fields would have to be
> > > retroactive which is not possible (you can't go and shield
> > > every speaker or device with a large magnet in it that's
> > > already been purchased), so the SSD's would have to be
> > > manufactured with some kind of far different "shielding" than a
> > > monitor due to the much stronger gauss of said devices. I
> > > guess that would have to be some kind of "cancellation magnet"
> > > around them sort of like shielded speakers have......but, I've
> > > never tried that to see how that would work. The cancellation
> > > device might have to be only around the magnet itself that's
> > > causing the field.
> > >
> > > I've built speakers before for monitor or TV use with drivers
> > > that were not shielded, and I was able to shield them using
> > > some kind of metal. I'm not sure what it was, it was NOT
> > > magnetic, at least it was not drawn to magnets. It looked like
> > > it had zinc in it.
> > > -Clint
> > >
> > > God Bless
> > > Clint Hamilton, Owner
> > > http://www.OrpheusComputing.com
> > > http://www.ComputersCustomBuilt.com
> > >
> > > ----- Original Message -----
> > > From: "David Grossman"
> > >
> > >
> > > Right, Clint.
> > > That's exactly what the computer industry did with monitors.
> > > They shielded
> > > them well enough to meet the standards.
> > > The problem with solid state drives is different, but if they
> > > can solve the
> > > radiation problem with monitors, they can do a comparable trick
> > > with drives.
> > > By the way, I don't know whether Energy Star has to do with
> > > radiation. It
> > > has to do with electricity consumption. Radiation standards are
> > > based on
> > > TCO.
> > > David Grossman
> > >
> > >
> > >> -----Original Message-----
> > >
> > >> I agree, but they still ARE a problem. I was mostly talking
> > >> about magnets more than stray EM fields from electronic
> > >> devices, and the only way to fix that is to make products
> > >> shielded from them, or make products that's not sensitive to
> > >> them. In the USA, all monitors now are "Energy Star"
> > >> compliant
> > >> which also might reduce radiation. http://tinyurl.com/6ptk9a
> > >> -Clint
> > >
> > >> ----- Original Message -----
> > >> From: "David Grossman"
> > >>
> > >> Electromagnetic fields do not have to be a problem.
> > >>
> > >> About 20 or 25 years ago, CRTs emitted a great deal of
> > >> radiation, causing
> > >> pregnant mommies who were exposed to the radiation for many
> > >> hours a day to
> > >> spontaneously abort their babies. The fledgling computer
> > >> giants
> > >> were
> > >> terrified that a wonderful industry with a great future would
> > >> go belly up
> > >> (perhaps I should have used a better expression!) and they
> > >> were
> > >> determined
> > >> to find a solution. They did - and the resulting and
> > >> ever-increasing
> > >> Scandinavian TCO standards are so stringent today that there
> > >> is
> > >> nothing to
> > >> worry about. Granted, flat screens largely replaced CRTs
> > >> today,
> > >> but that's
> > >> not the point - and even flat screens have to comply with TCO
> > >> standards.
> > >>
> > >> The industry reacted and solved the problem with one kind of
> > >> radiation
> > >> because they had no choice. They proved that with
> > >> determination
> > >> it is
> > >> possible to practically eliminate the threat of dangerous
> > >> radiation.
> > >>
> > >> When it comes down to it, electromagnetic fields are just
> > >> another kind of
> > >> radiation. The industry solved the problem with CRTs, and
> > >> they
> > >> CAN solve the
> > >> problem with solid state media.
> > >>
> > >> It's just an issue of determination and will-power.
> > >>
> > >> David Grossman
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