OT: Is This RF Or Power?

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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: http://home.comcast.net/~tjwatson1
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On Mon, 19 Jan 2004 20:46:24 -0500, Tom Watson wrote:

Aliens
-Doug
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On Tue, 20 Jan 2004 01:41:28 GMT, Doug Winterburn

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: http://home.comcast.net/~tjwatson1
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On Mon, 19 Jan 2004 21:25:53 -0500, Tom Watson wrote:
:-)
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On Mon, 19 Jan 2004 21:25:53 -0500, Tom Watson wrote:

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
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On Tue, 20 Jan 2004 01:41:28 GMT, Doug Winterburn

SPANISH RFI? That's a new one, 'cept for the AM stations.
- Every day above ground is a Good Day(tm). ----------- http://diversify.com Website Application Programming
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Tom Watson said:

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.
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On Mon, 19 Jan 2004 21:11:33 -0500, Greg G. wrote:

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: http://home.comcast.net/~tjwatson1
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Tom Watson said:

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 <may> 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.
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On Tue, 20 Jan 2004 01:19:17 -0500, Greg G. wrote:

Good point. An interesting observation is that all of the guys who are on CRT's in offices that share the wall with the metal fabricator's shop have "jumping screen".
The guys who are on laptops, in the same offices, do not have the problem.
The guys on the other side of the hall from the offices that share the fabricator's wall, do not have the problem. The problem seems to be specific to CRT's and seems to be related to proximity to the wall shared with the fabricator's shop.
The good news is that our company is building new offices and I have my name in to get one as far away as possible from the metal fabricator's space.
Thanks for the help.
Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website: http://home.comcast.net/~tjwatson1
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Given all that, the _real_ test is to temporarily run an extension cord from the _same_ outlet that one of the machines "on the other side of the hall", uses over to where -your- machine is. And see if _your_ screen still jumps when your neighbor's do.
Laptop LED/LCD/whatever displays are radically different in design than CRD displays, and are not subject to the same kinds of ideosyncratic behavior on -voltage- irregularities. Laptops essentially run off their batteries _all_ the time, with the line cord functioning as a battery charger. In effect, they're on a "full-time" UPS.
The machines across the hall could be on a different phase of the power distribution into the building. And the 'sag' is specific to the phase the machines 'next to the wall' are powered from.
If you can describe "exactly what it looks like" _when_ the 'screen jump' occurs, I may be able to provide better guesses. Does the picture pull in from the sides, so you see black at the right/left edges. possibly pulling in more in the middle, than at top/bottom (sort-of hour-glass like) and acts like a TV with the vertical hold out, probably "rolling" from the top down?
Or does the picture get 'twisted', and colors go "funny", with what _should_ be the same color showing as different colors at different parts of the screen? If you pull up something that makes the entire screen pure white, do you notice that the white is not the 'same shade of white' at all parts of the screen. i.e.,ill-defined areas of pale pastel colors?
The former is symptomatic of power problems.
The latter is symptomatic of magnetic impulse problems.
RFI (Radio Frequency Interference) typically shows up as an imposed 'pattern' on blocks of solid colors (herringbone/moire type stuff), and 'fuzzy' edges to things that should be sharp. Sometimes noticed as 'jitter' in a _horizontal_ direction.
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wrote:

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...
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Again, I don't think it's power-related, but to answer your question, 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
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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

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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
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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

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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.

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Borrow a small UPS and put your PC and monitor on it. Wilson

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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.

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$300 for an LCD monitor?
--randy
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