OT: Is This RF Or Power?

Aliens

-Doug

Reply to
Doug Winterburn
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I'm posting this here because:

  1. The problem is occurring in a wooddorking shop.
  2. There are a lot of computer dorks who are also woodorkers, who hang out here.

I'm working at my desk at the commercial wooddorking shop that I have come to work at and every once in awhile ( every two minutes) my computer screen jumps and is unreadable for a second.

It is my understanding that the shop next door is a metal shop and has a welder (of an unidentified type) that is against the wall that separates us.

I have not gone next door to see what kind of equipment they are running but the screen jump is very annoying.

Is the problem more likely to be a power problem or an RF problem?

How can I resolve the problem?

I have seen power strips that include RF filters and sell for about 50 bucks. I don't like getting into my pocket any more than the next guy but would do so if I could have some expectation of relief.

I look at spreadsheets all day, now and they are hard to read when they jump around.

Thanks.

Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website:

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Reply to
Tom Watson

It is probably a magnetic field from the welder transformer which is effecting the CRT, although it could be power related. I would move my desk to the farthest wall in any event. Those huge magnetic fields will give you brain cancer. ;-) You could try a LCD display, which would not be effected.

If it IS power related, and their wiring is separated from your building, you have problems not easily resolved.

In any event, distance is likely to be the only reasonable solution.

FWIW,

Greg G.

Reply to
Greg G.

Tom, Since you did not mention overhead lights dimming or the computer's UPS kicking in, I would guess that it is RF. From the effect you describe on the monitor to be caused by power there would have to be serious brown outs

How to check ? Move the comptuer -- use the same outlet via extension cord and move the computer accross the room. The RF effects will diminish with distance but power effects will travel with you (via the extension cord)

Cheers Eric

Reply to
SamTheCat

I gotchyur aliens right here for ya, Winterburn. (this is where the smiley face would go , if I knew how to make them).

Ah, well...

Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website:

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Reply to
Tom Watson

Hi Tom,

Difficult problem to guess at, so lets throw some logic into it. Pardon the endless questions ... I think you'll see where I'm going here.

If this is the only computer in your shop, pop your head next door and see if they have any computers, and if they are having the same problem. If you have other computers in your shop, are they showing this problem where they currently reside. If you can, move another computer to your work area (unplug all your stuff, plug the replacement in exactly, and observe).

Try another monitor for a short while on your computer. A failing component would explain the cyclic nature of the interference much better than pretty much anything in the other shop (unless they're running an automated spot welder all day).

Does the monitor make any noise when the screen wipes out? Does the picture get all twisted like when you hit the degaussing button? Does the monitor have this problem after the metal shop has shut down for the day/weekend? Do you shut the monitor off at night? If so, does the problem show up immediately after you turn the monitor on in the morning?

Take an AM radio and tune between stations. Set the radio next to the monitor and listen for any increased noise when the monitor starts its jumping routine. If you can hear the interference ... and it is cyclic, shut your computer down and see if the noise is still there (and still cyclic).

It takes a LOT of current to mess with a monitor. I had one CRT within 3 feet of a pair of cables connected to a high current battery discharge tester ... nominal 1800 amps would cause the whole video display to appear like it was being pulled and twisted from the back (a terrible wedgie to be sure). A defective battery that was only producing 700 amps didn't even ripple the screen. We switched to an LCD monitor and never saw another issue.

If nothing else, pull the workstation a couple feet away from the wall and observe any differences.

Plug an incandescent lamp into the same outlet strip as your monitor ... does it flicker along with the monitor?

Plug your entire computer into a drop cord that is fed from another breaker away from the ajoining shop wall.

***

I really don't know how to call this one ... so if you can fill in any of the blanks above, it will help resolve this.

Regards,

Rick

Reply to
Rick

Tom,

My experience with an electric welder was a bit more dramatic and it was due to RF. We were installing a satellite ground station out in Christmas Valley Oregon and the FAA called us one day to tell us our satellite dish was interfering with aircraft radio transmissions on their approach to Bend Oregon. Huh?...Says we...it isn't even powered up yet!

Upon further investigation, we found that the install crew had the covers off the generator/welder (trailer mounted puppy) to help keep it cool and it was wiping out the aircraft frequencies as they flew overhead.... It was probably wiping out the rest of the FM and HF bands to but we had the covers put back on and the FAA was happy (as I sure a few pilots were also).

So, yes it could be RF, magnetic and power-line induced. Try moving the computer and wearing tin foil hats to see if that helps...

Bob S.

Reply to
Bob S.

Reply to
Wilson Lamb

Tom,

Rick gave some excellent troubleshooting advice. Let me add one more thing. The video card in the computer could have an intermittant fault too.

Art

Reply to
Wood Butcher

magnetic field problem induced by the large current from the welder. I had a user once whose monitor was giving a "wavy" display. I went into the cube on the other side of the wall from her monitor and found a small desk fan. I turned the fan off and presto, no more interference. If a little fan like that can create enough of a magnetif field to cause her monitor problems, you can imagine what a welder would do. But I've got good news. I just saved a load of money by switching to GEICO. Also, magnetic fields dissipate by the inverse square of the distance from the source, so if you can move your monitor far enough away from the wall, you might eliminate the problem. The bad news of magnetic fields is that they're famously difficult to shield. As an alternative, you could switch to an LCD as another poster pointed out.

todd

Reply to
todd

:-)

Reply to
Doug Winterburn

Oh, I forgot to mention - I just bought one of those really 'spensive HF mig welders for $99. Hope the damn thing works for welding up the angle iron base for the charcoal Barbie :-)

-Doug

Reply to
Doug Winterburn

Here's what I don't understand. If the power surge coming form thief side is great enough, can it induce a surge in my wiring, even though we are not hard-wired together?

Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website:

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Reply to
Tom Watson

Eventually, you ARE hard-wired together. It is *supposed* to be at a point where this doesn't occur, but shit happens... ;-) That's why I said "you have problems not easily resolved."

For instance, if you are out in the sticks, and have a long, shared feed wire between the line transformer and your respective businesses, they could be superimposing surges onto your AC lines.

I am willing to bet it is electro-magnetic interference, however. I have a degaussing coil (which is an open air electromagnet used to remove magnetic fields from the shadow mask in a CRT) that will affect a computer CRT tube from 5 feet away. Walls don't influence its effect, unless they are solid steel. It doesn't draw anywhere as much power as a big welder transformer, but you get the idea...

Additionally, all newer monitors have what is known as a switched-mode power supply, as do computers themselves. These things convert AC to DC, then chop it into ~25kHz pulses used to drive the conversion transformer to derive the voltages actually used by the monitor's electronics. Pulse Width Modulation (PWM) is used to regulate the voltages to the desired levels, depending on load. These things are sometimes susceptible to hash on the AC line, although the better units are not. (I repair monitors, among other things...)

Monitors are pretty heavily shielded against emitting RF energy, and this also shields them somewhat against incoming RF as well.

I have a few ideas for you, however. Get a really long extension cord, and run between a suspected unaffected outlet and your system. If the problem remains, it probably isn't power related.

Move the computer system away from the suspicious welder. Magnetic fields drop precipitously with distance. If the problem goes away, it's probably magnetic fields affecting the monitor.

You could also have a failing monitor, I am assuming that it is O.K. The electrolytic capacitors in the aforementioned PWM power supplies go bad with age, and often cause jittery displays.

FWIW,

Greg G.

Reply to
Greg G.

you are hard wired together at some point- at the panel or all of the way out at the pole... 'twould take quite a surge to jump that, though...

Reply to
Bridger

through the magic of mutual inductance, a current on their side could induce a current in your wiring. The effect would be most pronounced if you had an electrical circuit running parallel and in close proximity to one of theirs that carried a large load. Honestly, I don't know the magnitude of the current that it could induce and I'm disinclined to look it up at this late hour.

todd

Reply to
todd

GSM cell-phone next to the monitor by any chance ?

Ray

Reply to
Ray

Reply to
tom

Best answer. It's both, really, though power, especially in the sticks, is the way to attack it. UPS for isolation, and let the alarm ring. My rural Co-Op is scrimping as new places are added, and though the drops do not go below 105V, the UPS on this computer is set for a % drop alarm.

Most welders fire and charge capacitors, which is the RF source.

Reply to
George

$300 for an LCD monitor?

--randy

Reply to
Randy Chapman

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