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Grex Tutoring Item 10: degaussing?
Entered by brenda on Sat Jun 3 05:46:37 UTC 1995:

What exactly is "degaussing"?  I know tv's do it, and that's why you're
not supposed to set videotapes, watches, calculators, etc. too close to
it.  Do computer monitors do the same thing?  I have some cassetted tapes
on a shelf about 6 inches above my monitor and 6 inches below my CPU
(yes, it's a kind of strange setup).  Should I move them?  Should I move
my disks that are about 2 feet away from the monitor and CPU?

thanks for the help in advance...

6 responses total.

#1 of 6 by mcpoz on Sun Jun 4 01:32:36 1995:

I am not sure technically what happens, but to degauss a tv screen (or monitor)
you pass it through (or near) an ac coil and the coil is active during the 
time it is near the screen and also as it is moved away.  The alternating
fields restore the screen to a non-magnetized state.  Automatic degaussers
must do essentially the same thing, probably with a fading electrical field.
Anyone know for sure?

#2 of 6 by srw on Sun Jun 4 05:37:11 1995:

You should definitely keep your disks away from magnetic fields.
Monitors (but not CPUs), audio speakers, and transformers are among the
common items that generate magnetic fields.

A residual permanent magnet can be induced in a picture tube, and a
magnetic read/write tape head also. This may be cancelled by "degaussing",
which immerses the object in an alternating Magnetic field.

TV tubes and most modern monitors do it automatically.
Some have a manual degaussing switch. 
You usually have to take your tape deck or VCR in for service
to get the heads degaussed if that becomes necessary.

#3 of 6 by rcurl on Sun Jun 4 06:19:29 1995:

Re #1: well, since you asked: the H magnetic vector is oscillated through
180 degrees which drags the B flux vector around its hysteresis loop.
As the H vector is diminished, the loop becomes smaller and smaller,
eventually leaving only much smaller residual B flux. I do not know 
how it is done automatically to a TV screen since it is not possible
for a TV tube to place a diminishing alternating magnetic field adjacent
to the screen - unless the magnetic field from the electron beam is
able to do it.

#4 of 6 by popcorn on Sun Jun 4 16:33:46 1995:

This response has been erased.

#5 of 6 by srw on Tue Jun 6 07:23:05 1995:

Hee hee. Yeah. Lot's of pretty colors.

#6 of 6 by dang on Tue Mar 26 03:59:34 1996:

re: 3 You know, we just studied mangetic fields, and electric fields, 
and even had a section on degausing, so I actually understood that. :)

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