I had a client who had some monitors that were flickering. The monitors were located adjacent to the network room that had some elctronic equipment installed along the wall. We had them move that equipment off of the wall and also install some magnetic shielding along the wall. The shielding reduced the readings from a range of 9-45mg to a range of 2-3.5mg. The client is telling me that he monitors are still flickering, any suggestions or comments?
Computer Monitor Flickering
- Thread starter bwyllie
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Computer Monitor Flickering
What kind of magnetic shielding did you use? I?m no expert in this area, but I once had to design an 18-wheel truck that was to house an MRI system. I recall that the magnetic shield was floor-to-ceiling covering all four walls, and included the ceiling and floor. It was broken only by the openings for doorways, viewing windows, and small penetrations. Did your shield go floor-to-ceiling and wall-to-wall?
What kind of magnetic shielding did you use? I?m no expert in this area, but I once had to design an 18-wheel truck that was to house an MRI system. I recall that the magnetic shield was floor-to-ceiling covering all four walls, and included the ceiling and floor. It was broken only by the openings for doorways, viewing windows, and small penetrations. Did your shield go floor-to-ceiling and wall-to-wall?
Re: Computer Monitor Flickering
The following were the sheets that were used:
CO-NETIC AA Perfection annealed sheets
? 0.025?thickness
? 30?H by 59?W
The sheets went floor to ceiling, but did not go the entire length of the wall, just the area where high levels were being measured.
The following were the sheets that were used:
CO-NETIC AA Perfection annealed sheets
? 0.025?thickness
? 30?H by 59?W
The sheets went floor to ceiling, but did not go the entire length of the wall, just the area where high levels were being measured.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Computer Monitor Flickering
I've seen that happen with a monitor "out in the middle of nowhere" so I doubt that you are on the right track with your magnetic shielding. They dumped the problem on the computer guy
Did you ever consider temporarily moving a monitor and computer away from the wall before you went through the trouble and expense of moving that equipment and installing magnetic shielding? Just by turning the monitor or moving it a few feet to another part of the desk should make a difference if it's a magnetic field that's bothering it.
If you suspect a power issue get yourself an extension cord and power the computer and monitor from a receptacle that powers another computer that doesn't have that problem BEFORE spending more money!
[ January 13, 2004, 01:23 PM: Message edited by: hbiss ]
I've seen that happen with a monitor "out in the middle of nowhere" so I doubt that you are on the right track with your magnetic shielding. They dumped the problem on the computer guy
Did you ever consider temporarily moving a monitor and computer away from the wall before you went through the trouble and expense of moving that equipment and installing magnetic shielding?
Just by turning the monitor or moving it a few feet to another part of the desk should make a difference if it's a magnetic field that's bothering it. If you suspect a power issue get yourself an extension cord and power the computer and monitor from a receptacle that powers another computer that doesn't have that problem BEFORE spending more money!
[ January 13, 2004, 01:23 PM: Message edited by: hbiss ]
- Location
- Illinois
- Occupation
- retired electrician
Re: Computer Monitor Flickering
Interaction between fluorescent lighting and some refresh rate settings on some monitors make them appear to flicker.
Don
Interaction between fluorescent lighting and some refresh rate settings on some monitors make them appear to flicker.
Don
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Computer Monitor Flickering
Right. And just to add to this, some refresh rates/ video card/monitor configurations result in flicker even in a dark room.
Right. And just to add to this, some refresh rates/ video card/monitor configurations result in flicker even in a dark room.
Re: Computer Monitor Flickering
don is right,
277 volt lights can make the monitors flicker. industrial plants can also make the power quality noisy - which will make the monitors flicker.
you need a good quality video card and monitor(i specify the multisync, non interlaced type).
try changing the display settings - resolution and then change the refresh rate - mine is set to 75 hz & 1024 x 768 true color. this filters out most problems we have here. there are some days that i have to change to 60 hz to eliminate the flicker.
don is right,
277 volt lights can make the monitors flicker. industrial plants can also make the power quality noisy - which will make the monitors flicker.
you need a good quality video card and monitor(i specify the multisync, non interlaced type).
try changing the display settings - resolution and then change the refresh rate - mine is set to 75 hz & 1024 x 768 true color. this filters out most problems we have here. there are some days that i have to change to 60 hz to eliminate the flicker.
catchtwentytwo
Senior Member
Re: Computer Monitor Flickering
We've run into this problem with monitors in switchgear rooms and found using a LCD (non-CRT) monitor seems to solve the problem. I imagine that might be less costly than shielding.
We've run into this problem with monitors in switchgear rooms and found using a LCD (non-CRT) monitor seems to solve the problem. I imagine that might be less costly than shielding.
catchtwentytwo
Senior Member
Re: Computer Monitor Flickering
Dereck,
Please elaborate on the "flip side".
Regards,
John
Dereck,
Please elaborate on the "flip side".
Regards,
John
karl riley
Senior Member
Re: Computer Monitor Flickering
If health effects are a consideration, making monitor changes does not adress the issue. Shielding only reduces fields from balanced, or non net-current, sources.
The remaining field is probably from a net current circuit, which is almost always due to some misconnection of a neutral. This needs to be checked out. Though I wrote a book on how to do this, the technique is basically to clamp an ammeter around all circuits in the area. They should read zero. If not, further checking will find the misconnected neutral. (in a nutshell).
Monitor flickering can happen from 5 to 12 mG (minimum) depending on the monitor.
Karl
If health effects are a consideration, making monitor changes does not adress the issue. Shielding only reduces fields from balanced, or non net-current, sources.
The remaining field is probably from a net current circuit, which is almost always due to some misconnection of a neutral. This needs to be checked out. Though I wrote a book on how to do this, the technique is basically to clamp an ammeter around all circuits in the area. They should read zero. If not, further checking will find the misconnected neutral. (in a nutshell).
Monitor flickering can happen from 5 to 12 mG (minimum) depending on the monitor.
Karl
- Location
- Bremerton, Washington
Re: Computer Monitor Flickering
Karl, welcome back.
All: Karl has been off somewhere (warm, I hope) for a while. I look forward to his help, especially on power quality issues, he has literally "written the book".
[ January 14, 2004, 12:25 PM: Message edited by: tom baker ]
Karl, welcome back.
All: Karl has been off somewhere (warm, I hope) for a while. I look forward to his help, especially on power quality issues, he has literally "written the book".
[ January 14, 2004, 12:25 PM: Message edited by: tom baker ]
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Computer Monitor Flickering
...we recommended moving the equipment but they were still worried about the health affects that field would have on employees
WHAT health issues? :roll: Their temporal lobe receives way more RF than if they lived next to a cell site!
...we recommended moving the equipment but they were still worried about the health affects that field would have on employees
WHAT health issues? :roll: Their temporal lobe receives way more RF than if they lived next to a cell site!
Re: Computer Monitor Flickering
I agree with you Hbiss but unfortunatly the employess are the ones that have heard about the health affects so now the employer needs to address it.
Karl, I appreciate yours and everyone else's input. I am also located in a very cold MA and would be interested in obtaining your contact info and possibly passing this along to the client(also in MA)in case they need further assistance or for any future potential clients.
I agree with you Hbiss but unfortunatly the employess are the ones that have heard about the health affects so now the employer needs to address it.
Karl, I appreciate yours and everyone else's input. I am also located in a very cold MA and would be interested in obtaining your contact info and possibly passing this along to the client(also in MA)in case they need further assistance or for any future potential clients.
karl riley
Senior Member
Re: Computer Monitor Flickering
hbiss, you ask what health issues. If I were to deliver to you all the scientific studies done on this in the last 20 years it would take an 18-wheeler, literally. Everyone can have an opinion and reaction, but hopefully after at least getting aquainted with some facts.
Just one citation: the IARC (International Agency on Research on Cancer), of the WHO, after an exhaustive review of the research, concluded in 2001 that a 4mG power-frequency AC magnetic field is associated with childhood leukemia in a causative way. They are a very conservative body.
Anyhow, since most high magnetic fields in buildings are due to NEC violations, why even argue the point? Why not correct the violations and everyone is happy?
Karl
hbiss, you ask what health issues. If I were to deliver to you all the scientific studies done on this in the last 20 years it would take an 18-wheeler, literally. Everyone can have an opinion and reaction, but hopefully after at least getting aquainted with some facts.
Just one citation: the IARC (International Agency on Research on Cancer), of the WHO, after an exhaustive review of the research, concluded in 2001 that a 4mG power-frequency AC magnetic field is associated with childhood leukemia in a causative way. They are a very conservative body.
Anyhow, since most high magnetic fields in buildings are due to NEC violations, why even argue the point? Why not correct the violations and everyone is happy?
Karl
karl riley
Senior Member
Re: Computer Monitor Flickering
Bwyllie,
My contact info is kriley3@ix.netcom.com/
The usual way to approach a high AC field situation is to take gaussmeter readings in a grid pattern. This will show the field pattern and give a good idea of source location and type.
Net current component can be identified by the rate of field weakening (takes about 3 measurements to determine). Shielding has no effect on net current.Fixing the error eliminates it.
However, high field sources such as transformers and switching equipment can be shielded. In this case, to keep costs low you need to identify the sources so you can shield them instead of the whole room or wall.
Karl
Bwyllie,
My contact info is kriley3@ix.netcom.com/
The usual way to approach a high AC field situation is to take gaussmeter readings in a grid pattern. This will show the field pattern and give a good idea of source location and type.
Net current component can be identified by the rate of field weakening (takes about 3 measurements to determine). Shielding has no effect on net current.Fixing the error eliminates it.
However, high field sources such as transformers and switching equipment can be shielded. In this case, to keep costs low you need to identify the sources so you can shield them instead of the whole room or wall.
Karl
karl riley
Senior Member
Re: Computer Monitor Flickering
Tom, I was in Paris, Barcelona and Palermo. Spent some awesome time standing on the sidewalk in Palermo and studying the external wiring going in and out of the masonry buildings. It made me realize that a city can still function in conditions which would cause all its buildings to be shut down if transposed to a US city.
More on that later.
Good to be back, I'll tell you!
Karl
Tom, I was in Paris, Barcelona and Palermo. Spent some awesome time standing on the sidewalk in Palermo and studying the external wiring going in and out of the masonry buildings. It made me realize that a city can still function in conditions which would cause all its buildings to be shut down if transposed to a US city.
More on that later.
Good to be back, I'll tell you!
Karl
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Computer Monitor Flickering
...If I were to deliver to you all the scientific studies done on this in the last 20 years it would take an 18-wheeler, literally. Everyone can have an opinion and reaction, but hopefully after at least getting aquainted with some facts.
Just one citation: the IARC (International Agency on Research on Cancer), of the WHO, after an exhaustive review of the research, concluded in 2001 that a 4mG power-frequency AC magnetic field is associated with childhood leukemia in a causative way...
Karl, that's all well and good but if any of it had any merit there would be regulations in place to deal with the issue like we have for smoking and lead for instance. At this point it's only raw research with lots of speculation and hype and absolutely no smoking gun. Maybe someday there will be proof, but there isn't any now.
My point to all of this is that until there are regulations we as electricians have no business setting ourselves up as self appointed experts on EMF remediation with knowledge we obtained on the internet.
We are not doctors, we are not physicists, we are not scientists. We are electricians whose job is to see that electrical energy is provided to the population in a safe and efficient manner in accordance with the present NEC and local regulations and that's all.
Until the NEC or local regulations require us to deal with EMF's and we have been formally educated on the why's and how it should be done it's not only not our job, but you are misleading your customers.
...If I were to deliver to you all the scientific studies done on this in the last 20 years it would take an 18-wheeler, literally. Everyone can have an opinion and reaction, but hopefully after at least getting aquainted with some facts.
Just one citation: the IARC (International Agency on Research on Cancer), of the WHO, after an exhaustive review of the research, concluded in 2001 that a 4mG power-frequency AC magnetic field is associated with childhood leukemia in a causative way...
Karl, that's all well and good but if any of it had any merit there would be regulations in place to deal with the issue like we have for smoking and lead for instance. At this point it's only raw research with lots of speculation and hype and absolutely no smoking gun. Maybe someday there will be proof, but there isn't any now.
My point to all of this is that until there are regulations we as electricians have no business setting ourselves up as self appointed experts on EMF remediation with knowledge we obtained on the internet.
We are not doctors, we are not physicists, we are not scientists. We are electricians whose job is to see that electrical energy is provided to the population in a safe and efficient manner in accordance with the present NEC and local regulations and that's all.
Until the NEC or local regulations require us to deal with EMF's and we have been formally educated on the why's and how it should be done it's not only not our job, but you are misleading your customers.
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