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Flickering Monitors?
Anonymous Coward writes "Our SB Office runs a small 2 Server network with 4 workstations in the LAN, each connected to a dedicated APC Surge protector. The building has a backup power generator thus we didn't see the need for a UPS. For some odd reason all our monitors flicker a lot. We've tried everything from changing resolutions/refresh rates/video cards/monitors and spacing the monitors farther apart from each other - all to no avail. Could this be a building power supply problem? Some have suggested there may be some magnetic interference but visually inspecting the surroundings doesn't leave us with a culprit for the cause. Could this be fixed by the simple addition of a good UPS? Any help, tip or information would be gladly appreciated. Thank you."
Any of your questions could be the culprit, and if that is the case, a separate UPS for the monitors would likely fix the problem.
But you don't say what type of monitors these are, or their age. Which brings us to the question: ARe these just crappy, cheap monitors?
I have developed a set of debugging techniques over the years that seems to work in most every situation. It's a matter of looking at a problem from the proper level of abstraction and using the tools I already know how to use:
How do you find a needle in a haystack?
With all seriousness, pick up a good compass at a sporting goods store and do a survey of your office. Walk around the room and see if there are any deflections. Whether it's an electric current (which induces a magnet field) or an actual magnet in near proximity to the magnet,
a good compass should point you in the right direction (pun intended!)
Things I have experienced in the past which affected my monitors, in no particular order:
One other thing to try is to bring the PC, monitor, and all peripherals home and see if the problem exists there, too. If so, then it's likely there's something flakey about your equipment. If they are okay, then it would indicate there's some environmental factors at your office.
Good luck! And please fill us in on what you find!
No, it is not two phase. It's single phase. Bear with me and I'll explain:
The power company transformer has a secondary winding with a grounded center tap. The voltage between the two poles of the transformer is 240V; the voltage between one pole ant the center tap (ground) is 120V. The grounded "neutral" wire is connected to this center tap.
If you hook up a scope between pole "A" and neutral, then hook it up to pole "B" and neutral, (providing the neutral is connected to the same pole of the scope) you will find that one is the INVERSE of the other, or reverse polarity. They are not 180 degrees out of phase, because YOU have reversed the polarity in hooking it up. Connect the scope between the two poles, and you will find a 60Hz sine wave of twice the amplitude (240V) as between one pole and neutral. There is no point to 180-degree 2-phase, because summed with cross polarity you get 0V and summed with same polarity you get single phase twice amplitude.
If there was a two-phase situation, you would see a sine wave that is the sum of two sine waves, offset by 120 degrees from each other. No point to this, because the resulting waveform is ugly and inefficient.
Three phase power is used primarily for electric motors. For a given power rating, a 3-ph motor can be made smaller and cheaper, runs cooler and more efficiently, and has greater starting torque than a 1-ph motor. Besides, a 3-ph motor can be reversed easily.
Occasionally in a commercial or industrial setting, you will find lighting which is "208" or "277" volts (odd numbers, hey?). This is because they are running from different legs of a 3-ph transformer bank than your ordinary stuff.
Back to the 1-ph system... it's not truly a neutral wire unless the loads on both poles of the transformer are equal. In a 120V circuit, it is NEVER a neutral wire because it is carrying current back to the power source.
In spite of the fact that the "neutral" wire (properly termed, "grounded current-carrying conductor") carries current, the potential between it and ground should always be zero. Anything else indicates a very serious and hazardous problem. If this center-tap wire fails between the transformer and your electrical panel, you may get a situation where the voltage between pole A and ground is greater than pole B and ground (depending on load), summing to 240V. This is a very dangerous situation (kills every appliance and computer and in the event of a ground lift energizes the metal frames of everything) and if you have it, turn off ALL POWER NOW and call either an electrician or the power company immediately.
Give me my freedom, and I'll take care of my own security, thank you.
i once visited a scene shop in the theatre of a local university and the technical director there showed me one of the most dangerous things I have ever seen.
They had an older style table saw, the type that rarely has a blade guard (nor can you use them anyways when ripping an 8' piece of ply). He powered it up once, it ran normally. He turned it on or off a couple more times, and finally said "Got it". Though I could distictly here that the saw was on, the blade appeared not to be spinning. When he slid a two by four into the blade it slowedthe rotation down just enough that you actually could see the blades turning, though it was in a funny oscillatiion, like dancing in a high speed strobe light. Turns out, the flourescent lights flickered at just the right frequency to make the moving blade appear to be standing still.