electron gun(s) and magnetic fields

[Gary DeWitt]

I have a 54" RCA rear projection. I had a new hardwood floor installed
with an electric heating grid underneath. The grid consists of heavy
screen mesh, similar to window screen but 2-3 times heavier wire, laid
in one continuous circuit back and forth across the room. There is a
high voltage, low amperage current running through it. Here's the
problem - when the heater is on, the guns in my tv misalign, looks
like 3-d image viewed without the correct glasses. Soon as I turn off
the heat, the tv returns to normal. How can I shield the tv from the
floor induced field? Faraday cage? (I don't really want to view thru
wire mesh!) Grounded sheet of steel under the set? Raise the set a
foot or two off the floor? Both? Any suggestions, particularly from
those who have solved this problem or engineers, would be greatly
appreciated!

Real E-mail: gpdewitt at earth link dot net (no space in earthlink)

 

[NSM]

| I have a 54" RCA rear projection. I had a new hardwood floor installed
| with an electric heating grid underneath. The grid consists of heavy
| screen mesh, similar to window screen but 2-3 times heavier wire, laid
| in one continuous circuit back and forth across the room. There is a
| high voltage, low amperage current running through it. Here's the
| problem - when the heater is on, the guns in my tv misalign, looks
| like 3-d image viewed without the correct glasses. Soon as I turn off
| the heat, the tv returns to normal. How can I shield the tv from the
| floor induced field? Faraday cage? (I don't really want to view thru
| wire mesh!) Grounded sheet of steel under the set? Raise the set a
| foot or two off the floor? Both? Any suggestions, particularly from
| those who have solved this problem or engineers, would be greatly
| appreciated!

Interesting!

1. The higher off the floor the TV is, the lesser the effect.

2. Alternate layers of sheet steel and aluminium under the TV, insulated
from each other by paper, might diminish the effect.

3. Use a separate heater when you want to watch TV.

N

 

[N Cook]

I have a 54" RCA rear projection. I had a new hardwood floor installed
with an electric heating grid underneath. The grid consists of heavy
screen mesh, similar to window screen but 2-3 times heavier wire, laid
in one continuous circuit back and forth across the room. There is a
high voltage, low amperage current running through it. Here's the
problem - when the heater is on, the guns in my tv misalign, looks
like 3-d image viewed without the correct glasses. Soon as I turn off
the heat, the tv returns to normal. How can I shield the tv from the
floor induced field? Faraday cage? (I don't really want to view thru
wire mesh!) Grounded sheet of steel under the set? Raise the set a
foot or two off the floor? Both? Any suggestions, particularly from
those who have solved this problem or engineers, would be greatly
appreciated!

Real E-mail: gpdewitt at earth link dot net (no space in earthlink)

2 ideas
Find someone who has a heap of mu-metal sheets and lay under TV

or trace with sniffer or pipe/metal detector the exact run of heater wires
at a point away from TV. Excavate down and cut and bypass the few loops
that go under the TV

electronic hints and repair briefs , schematics/manuals list on
http://homepages.tcp.co.uk/~diverse

 

[Charles Schuler]

Any iron or steel (but not stainless steel) shield (such as sheet metal)
that you can place between the heater and the TV will help. Iron has much
lower reluctance than air, so the magnetic field from the heater will be
concentrated in the shield. Stainless steel is weird in this regard and
usually won't help even though it can be made up of mostly iron.

 

[Sam Goldwasser]

I have a 54" RCA rear projection. I had a new hardwood floor installed
with an electric heating grid underneath. The grid consists of heavy
screen mesh, similar to window screen but 2-3 times heavier wire, laid
in one continuous circuit back and forth across the room. There is a
high voltage, low amperage current running through it. Here's the
problem - when the heater is on, the guns in my tv misalign, looks
like 3-d image viewed without the correct glasses. Soon as I turn off
the heat, the tv returns to normal. How can I shield the tv from the
floor induced field? Faraday cage? (I don't really want to view thru
wire mesh!) Grounded sheet of steel under the set? Raise the set a
foot or two off the floor? Both? Any suggestions, particularly from
those who have solved this problem or engineers, would be greatly
appreciated!

A Faraday cage won't help. It's magnetic interference and magnetic
fields are difficult to block.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

 

[Sam Goldwasser]

sorry, i don't think you can.

you would have to align the TV with the heat on and then align it
again after.

That won't help if the heating grid is powered from AC.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

 

[Art]

Also the Manufacturer will be absolutely no assistance regarding this since
the symptom is being induced by it's environment. As noted, you may want to
consider a DLP, MMD, or Plasma television reciever. Or, move the curent
television to a room that is not heated in such a manner to resolve that
particular problem.

 

[Jamie]

sorry, i don't think you can.
you would have to align the TV
with the heat on and then align
it again after.
the only thing i can think of is
that the electric heaters are
not properly laid out over
laying each other to cancel each
other out which in this case
can be hard to do..
you could try elivating the
tv on a stand or get your
self a DLP projection.

 

[Graham]

I have a 54" RCA rear projection. I had a new hardwood floor installed
with an electric heating grid underneath. The grid consists of heavy
screen mesh, similar to window screen but 2-3 times heavier wire, laid
in one continuous circuit back and forth across the room. There is a
high voltage, low amperage current running through it. Here's the
problem - when the heater is on, the guns in my tv misalign, looks
like 3-d image viewed without the correct glasses. Soon as I turn off
the heat, the tv returns to normal. How can I shield the tv from the
floor induced field? Faraday cage? (I don't really want to view thru
wire mesh!) Grounded sheet of steel under the set? Raise the set a
foot or two off the floor? Both? Any suggestions, particularly from
those who have solved this problem or engineers, would be greatly
appreciated!

Swap your rear-projection TV for a Plasma or LCD.
Or use an alternative heat source.

I am not trying to be flippant, if the convergence shift is as bad as you
say, I don't think you will ever shield it.

 

[JURB6006]

Here's an idea that'll blow you f______ mind

An RCA doesn't need gravity to cool the CRTs, so, turn it upside down.
Unfortunately you'll have to make a top for it and have it completely re-setup
for this mode, but this will put the CRTs at the top, well away from the EMI.
To get the desired screen height you might not really be able to put anything
on top of it, the speakers will be at the top (and reversed, but you know what
to do), and I would suggest a carefully designed cooling system. Yes a fan, but
with it setup to draw air the right way through the chassis.

In this case, this is the best I can do. If you're in NE Ohio I can do it for
you, probably pretty reasonable. I'm not really that cheap, but it'll be well
less than getting a DLP, and don't get a plasma until they perfect them.

Just build whatever stand it takes to get the screen as high as you want it,
and BTW, all the stuff that used to be on top could now be on shelves
underneath.

While this might be a fine example of lateral thinking, it may or may not be
right for you, but it is an idea.

JURB

 

[Asimov]

"Sam Goldwasser" bravely wrote to "All" (12 Nov 04 16:04:32)
--- on the heady topic of "Re: electron gun(s) and magnetic fields"

SG> From: Sam Goldwasser <[email protected]>

I have a 54" RCA rear projection. I had a new hardwood floor installed
with an electric heating grid underneath. The grid consists of heavy
screen mesh, similar to window screen but 2-3 times heavier wire, laid
in one continuous circuit back and forth across the room. There is a
high voltage, low amperage current running through it. Here's the
problem - when the heater is on, the guns in my tv misalign, looks
like 3-d image viewed without the correct glasses. Soon as I turn off
the heat, the tv returns to normal. How can I shield the tv from the
floor induced field? Faraday cage? (I don't really want to view thru
wire mesh!) Grounded sheet of steel under the set? Raise the set a
foot or two off the floor? Both? Any suggestions, particularly from
those who have solved this problem or engineers, would be greatly
appreciated!

SG> A Faraday cage won't help. It's magnetic interference and magnetic
SG> fields are difficult to block.

A magnetic field is impossible to block, however it can be readily
redirected. If the tv were completely enclosed in an iron box the
interfering AC field would flow around the tv and through the iron
instead. This may not be very practical however, after all the screen
needs to be seen to be of use. Perhaps a metal shelf could work but
this is often a cause of colour purity problems in itself.

There are other strategies, for example we all know magnetic field
intensity decreases as the square of the distance. Therefore raising
the tv away from the floor enough may be all that is needed. Perhaps
leaving a sheet of iron on the floor below the tv's stand would
further decrease the field even more in the vicinity of the tv.

Another idea would be to induce a small field under the tv with the
opposite phase in the hope that the second field would cancel the
first enough to allow the tv to operate properly. Maybe just a few
loops of wire wound under the base of the tv would be enough for the
same effect. Of course phasing the small cancellation field would be
trial and error or how for example it should be oriented.

However, as a side issue, one concern I might have would be of living
in a space with such a significant magnetic environment that it
noticably affects the tv. I've heard of people living over transformer
rooms having a myriad of problems from infertility on through to
childhood leukemia. Then again people have been using electric
blankets for ages and I don't think any co-relation has been shown
there. It's a concern I really don't feel qualified to comment about.

A*s*i*m*o*v

.... Inductor designers do it in the gap.

 

[Gary DeWitt]

2 ideas

Find someone who has a heap of mu-metal sheets and lay under TV

What is mu-metal, and is there a source where it can be salvaged from?
I saw something like this on the web, poorly described and priced at
hundreds per square foot!

 

[Sam Goldwasser]

What is mu-metal, and is there a source where it can be salvaged from?
I saw something like this on the web, poorly described and priced at
hundreds per square foot!

Mumetal is a highly magnetically permiable material. However, it's expensive
as you note, and difficult to work (you can't bend it without reannealing for
maximum effectiveness).

And, since you can't see through it, at least the front of your TV
will be exposed. If it is simply put under the TV but the magnetic field
will still come in from the beyond.

You will end up spending much more on bandaids than on an LCD TV.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.

 

[Charles Schuler]

Any iron or steel (but not stainless steel) shield (such as sheet metal)
that you can place between the heater and the TV will help. Iron has much
lower reluctance than air, so the magnetic field from the heater will be
concentrated in the shield. Stainless steel is weird in this regard and
usually won't help even though it can be made up of mostly iron.

Additional information:

"So, in our example of placing a steel plate between the magnet and the area
we desire to shield from the magnetic field, the ends of the steel plate
will have all the flux lines possible trying to get into it, traveling down
to where they must exit to get back to the magnet (the flux channel) and
exiting in a big bunch. Remembering that the more flux lines, the stronger
the field, what we have accomplished with our actions is to make the
magnetic field near the ends of the steel plate stronger (collected flux
lines) and more inhomogeneous (bent more). Both of these points make the
stray magnetic field more of a problem near the ends of the steel plate. One
way to overcome this problem is to make the steel plate much larger that the
desired area to shield. As the dimensions of the steel plate get larger, the
larger the area of the lowest magnetic field behind the steel plate."

It would seem that if the steel plate was large enough, the flux lines at
its edges should be far enough away from the electron guns and the problem
will be solved or at least greatly reduced.

Source: http://www.acornnmr.com/appnotes/shielding.htm

 

[NSM]

| Mumetal is a highly magnetically permiable material. However, it's
expensive
| as you note, and difficult to work (you can't bend it without reannealing
for
| maximum effectiveness).

And a cheaper alternative is alternate layers of steel and aluminium,
insulated with paper.

NM

 

[James Sweet]

Here's an idea that'll blow you f______ mind

An RCA doesn't need gravity to cool the CRTs, so, turn it upside down.
Unfortunately you'll have to make a top for it and have it completely re-setup
for this mode, but this will put the CRTs at the top, well away from the EMI.
To get the desired screen height you might not really be able to put anything
on top of it, the speakers will be at the top (and reversed, but you know what
to do), and I would suggest a carefully designed cooling system. Yes a fan, but
with it setup to draw air the right way through the chassis.

In this case, this is the best I can do. If you're in NE Ohio I can do it for
you, probably pretty reasonable. I'm not really that cheap, but it'll be well
less than getting a DLP, and don't get a plasma until they perfect them.

Just build whatever stand it takes to get the screen as high as you want it,
and BTW, all the stuff that used to be on top could now be on shelves
underneath.

While this might be a fine example of lateral thinking, it may or may not be
right for you, but it is an idea.

JURB

I would be concerned about coolant leaking and airflow for cooling, not to
mention this would look pretty ugly. I think it'd be easier to set the TV up
on something, a shelf a foot off the floor would probably be plenty, it's
worth a try, cinder blocks and a piece of plywood will do the trick,
something nicer looking can always be built once the problem is fixed.

 

[Jim Adney]

the only thing i can think of is
that the electric heaters are
not properly laid out over
laying each other to cancel each
other out which in this case
can be hard to do..

I agree with this. I don't know if the makers of this kind of heater
have thought of this problem, but they should have. It should be
possible to lay the heating material in such a way that the external
field is minimized, but it sounds like this was not done in your case.

It might be worthwhile to check with the maker of your heater to see
if they have guidelines in installing it. I have no idea how hard it
might be to get it corrected.

I agree with Sam, that trying to shield it is likely to be futile.

-

 

[Jim Adney]

An RCA doesn't need gravity to cool the CRTs, so, turn it upside down.

Very interesting, and creative, suggestion. It's a lot of work, but
probably a lot less than digging up the floor.

It's also possible that it would not help significantly. It all
depends on the nature of the mag field set up by the heating coils.

-

 

[Graham]

the only thing i can think of is
that the electric heaters are
not properly laid out over
laying each other to cancel each
other out which in this case
can be hard to do..
you could try elivating the
tv on a stand or get your
self a DLP projection.

I see, you mean like a bifilar coil?

Is that standard practise with underfloor heating?

We don't see much of it now here in the UK.

Was put in to apartments in the '60's but became notoriously expensive to
run.