Electric/Magnetic Effect?

[Rilescat]

Ok...this question sounds simple, but it may not be quite so simple.

If you place two monitors next to each other, turn one on, then turn the other on, the first monitor will ripple and flicker. I have found this with new and old monitors (CRT) alike.

Why exactly does this occur, and why does this usually only occur when powering up the second monitor? EMF is the simple way of explaining it, but what is the complex way? AND.....what type of tool can I use to measure this electrical discharge?

Thanks all!!!

 

[Demon-Xanth]

Well, the complex way summarizes down to the simple way

But a magentic field disperses by the square of the distance. Double the distance, quarter the power. If the monitors are a fair distance away the power is negligable, but put the yokes next to eachother and all hell breaks loose. The yoke is actually typically dead center of the monitor (by nature). A yoke is what actually moves the electron beam(s) along the screen and paints a picture. The reason for the flicker is that the other yoke has enough power to moderately jerk the neighboring monitor's beam(s) around given the distance. Not all monitors do this, many have good shielding and don't transmit enough power, and don't let enough power in, to noticably affect eachother. Some however, are VERY noticable.

There actually are devices that can measure a magnetic field, hall devices are one example.

 

[CTho9305]

i dont think thats what he's referring to. I think it is the result of monitors "degaussing" themselves on poweron. deguassing demagnetizes the CRT's parts with a VERY powerful electromagnet (simplified cause I dont understand exactly why it works ).

the powerful magnetic field causes the distortion on the nearby monitors. if you wait 15 minutes or so and then degauss one of the monitors, you should see the other flicker.

 

[Chooco]

i think i heard this somewhere, but here i go. the monitor has tons of electrons flowing over the surface which is a magnetic field. if you put aluminum foil on the surface of the monitor, it acts like the negative in a circuit and you can actually light a bulb with it. putting the monitors together is like putting a magnet to either monitor. it does not matter if you put the negative or the posative pole to the field, it will still disrupt it and f*** your monitor up.

i think you can measure the intensity of the field just by hooking one end of an ampmeter to the screen of the monitor and the other end to a ground or something like that to measure how many amps it is. i don't remember exactly but i THINK that the intensity of an electric magnet can be measured just by measuring the current in amps flowing through the material in question.

 

[zephyrprime]

magentic field disperses by the square of the distance

Magnetic fields are dipoles so they have a field strength that is proportional to the inverse cube of distance, not the inverse square.

 

[RatedR]

I'd like to add a question to the thread if you don't mind. What about multiple monitor setups? I haven't read much about multi-crt setups, but my guess would be that this is an all too familiar problem. Multiple CRT-Monitor setups are becoming more common everyday, how would a potential Multi'r *like myself* avoide such issues as magnectic interferance or whatever you guys were talking about .

Are there newer monitor models out that cut back on the amount of interferance? And for the people that are using older monitors, are there tips to help remedy the problem?

 

[rimshaker]

I think you guys are missing the very basic physics principles in this situation. When the 2 monitors are close enough in proximity, the large initial magnetic field causes a significant electric field to appear in the other monitor. Remember that electric/magnetic fields are closely intertwined. When one is present, the other is induced automatically. The induced electric field would naturally cause a temporary disturbance with the steady-state operation of the first monitor.

 

[evilOlive]

Originally posted by: RatedR
I'd like to add a question to the thread if you don't mind. What about multiple monitor setups? I haven't read much about multi-crt setups, but my guess would be that this is an all too familiar problem. Multiple CRT-Monitor setups are becoming more common everyday, how would a potential Multi'r *like myself* avoide such issues as magnectic interferance or whatever you guys were talking about .

Are there newer monitor models out that cut back on the amount of interferance? And for the people that are using older monitors, are there tips to help remedy the problem?

That's a really good question which I've never thought about. Too bad I don't know the answer

EMI is created whenever there is electricity being induced. The monitor will flicker whenever it is in the presence of a secondary large electrical device, which induces its own magnetic field. For example, take a large fan or something with a motor which has a good magnetic field and place it near the monitor, it will jitter like crazy.

 

[Demon-Xanth]

Use good monitors, I have a pair of Viewsonics and a PB 14" in a triple display setup w/ no visual problems.

 

[Jerboy]

It's the 60Hz magnetic field from degauss coil. Monitor degauss itself by applying 60Hz magnetic field on its shadow mask on each cold start.


CTho9305, it is not VERY powerful. It simply apply alternating direction magnetic field to cancel out magnetization that has formed over the shadow mask. Compared to magnetic field used to turn rotor in washer motors or in MRI, it is not strong.

 

[CTho9305]

Originally posted by: Jerboy
CTho9305, it is not VERY powerful. It simply apply alternating direction magnetic field to cancel out magnetization that has formed over the shadow mask. Compared to magnetic field used to turn rotor in washer motors or in MRI, it is not strong.

compared to the field used to create an image on a CRT, it is, and thats what matters here

(It does distort nearby screens as much as a bulk tape demagnetizer....)

 

[Rilescat]

All very excellent info/ideas guys!!

Now, does anyone know what type of equipment I need to be able to actually measure the electrical/magnetic discharge from a monitor? Demon-Xanth
mentioned "hall devices", but I don't know what those are.

Please educate me!

Thanks