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From: "Michael Lamond"
Subject: Re: Interference from power lines
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
NNTP-Posting-Date: Tue, 07 Jan 2003 13:51:33 GMT
Organization: AT&T Worldnet
Date: Tue, 07 Jan 2003 13:51:33 GMT
"John Wilson" wrote in message
> Charles Perry wrote:
> > "daestrom" wrote in message
> > news:hbrS9.216177$Vz2.firstname.lastname@example.org...
> >>Moving a monitor's orientation or from one side of the room to
> > would
> >>have an effect if it were caused by a stray E-M field from outside.
> >>wonder if the fault that happened caused some damage. Were the
> >>normally left on (perhaps in power-save mode) over the holiday? If
> >>was some sort of voltage brownout or spike, perhaps they were
> >>Is the voltage supply at the wall outlet normal? Perhaps a low
> >>(because of the temporary rig that LIPA put in) is enough to run
> >>and power monitor, but not enough for proper operation? Easy to
> > This is going to sound odd, but we had a case in Florida once where
> > buildings structural steal had become magnitized during a fault. It
> > driving the monitors in the building (near the affected wall) crazy.
> > that one was hard to find. It was a DC field of course and did not
> > waviness as much as it did an odd slanting offset.
> > Charles Perry P.E.
> My favorite along these lines was watching in the control room of a
> large magnetic fusion machine. When the machine operated, magnetic
> fields would ramp up over about three seconds, and the plasma would
> pulse at the end of that ramp. You could watch the pictures on all the
> monitors twist and shift off the screens as the field ramped up, then
> come back to normal at the end of the shot.
Now you've reminded me of two separate cases of color CRTs mounted
in control panels that were affected by magnetic fields. The first time,
steel enclosure must have been welded with DC, because the screens
in all four panels were affected only when installed. We had the motor
shop wind a big coil, fed it from the variac and had one of the wiremen
move the coil over the surface until the magnetic fields were gone. The
second one was an industrial PC in the control panel for a water chiller
that faced the autotransformer starter for 5000 HP 4160 volt compressor
motor. Whenever the chiller was started, the transformer's magnetic
distorted the screen beyond recognition until the run contactor closed.
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