Re: Magnetic Interference

[Frank Muennemann <frankm@resonex.com>]

> Have any RADSAFE subscribers experienced magnetic field interferences 
> from transformers, etc. with regard to VDT's.  I've only dealt with ELF 
> and VLF along IRPA Guidelines, not protecting Dr. Fuddpucker's Mac 
> display...
 
Resonex is an MRI manufacturer.  Because MRI scanners are very 
sensitive to ambient magnetic fields, we routinely check prospective
sites before installing a machine.  Large color monitors such as the
ones we use for our operator's console (a 19" model) will tolerate
about 1 Gauss fields before some color distortion becomes visible. 
At several Gauss field, the display looks really ugly. I suspect that
the monitors are manufactured to just barely tolerate the Earth's
magnetic field (less than 0.6 Gauss in most places).

Many MRI scanners (but not Resonex's!) have substantial external
magnetic fields which make it impossible to operate color displays
nearby.

Electrically powered subways can be a spectacular source of interfering
magnetic fields.  I talked with a Salvation Army member in New York
City who said that he had set up VCR's showing informational videos
in a soup kitchen.  As it happened, the soup kitchen was below street
level near a subway line--- the displays were unviewable whenever
a train went by.

-- 
Frank Muennemann | 'I speak for myself only' as: frankm@resonex.com