From: "Tom Del Rosso"
Subject: Interference from power lines
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
NNTP-Posting-Date: Mon, 06 Jan 2003 02:32:24 GMT
Organization: AT&T Worldnet
Date: Mon, 06 Jan 2003 02:32:24 GMT
If anyone can make sense out of this, please reply.
On Wednesday, 1/1, the power lines right outside an office fell to the
street, still alive. They were repaired but the next day, in the office
of 11 computers, all but 3 monitors have wavy screens to various
degrees, from annoying to severe. The office is atop an incline, so
it's at the height of the power lines, but they are still 50 feet away.
The location is Long Island, NY, and the provider is LIPA. The
interference continued at least through Friday.
My first thought was magnetic interference, but there is no high-power
equipment inside, except for one unplugged electric heater. The
monitors least affected are on opposite sides of the office, and so are
the monitors most affected. Moving a monitor made no difference to it,
so there is no correlation with position within the room. (There is a
relation to vertical frequency, with lots of interference on one
previously good monitor when it was changed to low resolution (that
monitor doesn't display frequency unfortunately), but other monitors
were sensitive at all frequencies.)
Because it was spread out so, I thought it might be electrically rather
than magnetically coupled. The line voltage was a little unstable,
varying from 111 to 115 VAC from minute to minute. I was using a Fluke
79 (not true RMS). I tried unplugging 2 of the computers' UPSs and
letting them run on battery but there was no change in their
interference, so it must be magnetically coupled.
For the short time they were on battery, both UPS outputs dropped below
95 volts, so I guess they were left on and the batteries were killed
during the blackout. I considered that maybe the monitors were
permanently damaged, but unlikely I thought. In spite of the sudden
drop in voltage when switching to battery, the monitors I tested that
way didn't even twitch, but continued their steady low frequency waves.
If it's still happening Monday I'll try bringing in a new monitor. I
didn't get a chance to swap the best and worst of them, so I'd like to
try that too. Any other suggestions? What could cause that kind of
-If emailing please delete the first 3 words-