Case windows & EMI

[cmetz]

Looking at cases that are available, more and more have acrylic "windows" or other plastic/transparent regions that don't have metal behind them.

Silly me, I thought that surrounding all your PC components with metal that touched the presumably grounded metal case of the power supply made a nice Faraday cage-ish shield - helping protect the PC against EMI coming in and helping to protect everything outside the PC from EMI going out. Cutting out some metal and replacing it with plastic would reduce or eliminate this effect. On a packaged system, this might cause you to fail FCC certification (depending on how you're doing things).

Am I missing something, or am I right to think that people are choosing "cool looking" over "the electrical/magnetic right thing to do."

 

[paco83]

Well Dell's cases are plastic. Although they might spray the inside of the case with conducting paint to help make up for it. I would think that most cpu's these days aren't as prone to EMI interference.

 

[BG4533]

I don't think it is a big issue if one at all. People have asked this question before and no one gave any conclusive evidence of windows causing problems.

 

[sep]

Anyone got an EMI meter to test? Radio Shack sells them.

Anandtech - Do you or any partnering review site want to tackle this? :beer:

 

[deerslayer]

Originally posted by: BG4533
I don't think it is a big issue if one at all. People have asked this question before and no one gave any conclusive evidence of windows causing problems.

 

[piasabird]

I think they are more worried about emissions getting out than emissions getting in!!!

Most metal cases have plastic on the front anyway. When you put a couple of lights inside that alone can deaden quite a bit of emissions.

Think about this:

Your monitor is probably plastic and puts out more immissions than the computer!

Of course if you put a metal case over the screen, you will not see much!!!

 

[Demon-Xanth]

Behind the plastic on most cases is metal. And the frequency that your monitor works at is much different from your PC. The largest reason for EMI testing is for emmissions and not susceptibility.

 

[Jeff7]

Originally posted by: sep
Anyone got an EMI meter to test? Radio Shack sells them.

Anandtech - Do you or any partnering review site want to tackle this? :beer:

I have an EM field detector - Electronic Goldmine was selling them for $2.95 each awhile ago, sold out now though, maybe I'll post a pic sometime - anyway, your monitor probably puts out a LOT more EM radiation than your PC. The EM field that the detector picks up from my monitor (and any CRT-based display I've tested) extends well over a foot and a half at "high" (as far as the detector goes) intensity. My PC's EM field extends under 6 inches at the same intensity - and that's with the case off entirely.

And besides, how often does the FCC make house calls?

 

[Texun]

Never read anything about them causing problems, but my concern for shielding would be to keep off-air RF from getting in. Think outside the box for a minute.... many cordless phones now operate at 2.4Ghz. I would like to know what would happen if the phone were placed close to an unshielded cpu? Maybe nothing that the user would notice, but boards have a range of other frequencies that off-air transmissions could corrupt if not blocked properly. ATA is 33, 66, 100, and 133 and the flat ribbon cables are not shielded. Ever wonder why the length of ATA cables has a spec? Reflections in the cable can cause data corruption depending on the wavelength. It probably isn't enough for the user to notice, but for mission critical environments I am sure engineers provide correct shielding.

 

[EeyoreX]

It probably isn't enough for the user to notice, but for mission critical environments I am sure engineers provide correct shielding.

I think you hit the nail on the head. I doubt many (any?) engineers in mission critical situations are buying cases with windows. Since it is probably only the end user buying these cases, you are probably right that the issue (if there really is one) is really a non-issue.

\Dan