Perspex cases and EMI

[downhiller80]

Is having a 12" square perspex window in a case going to result in a lot of stray EM waves in a room? What if you have 10 such cases in an office? Is it anything to be concerned about or not?

 

[Joker81]

Google is your friend

For Pentium 4 CPUs scaling above 2GHz, a special EMI grounding frame will be required. The frame will protect the CPU from receiving and transmitting electromagnetic interference. At 2,000+ MHz, the Pentium 4 core could produce massive levels of EMI radiation. While not harmful to humans (in these low amounts), the increased EMI could disrupt operations of system peripherals and other close-by electronic devices. Intel has planned ahead by requiring all OEM vendors to include the grounding frame in any of their high-speed P4 systems.

So I don't think you should have to worry. At least for your self.

 

[Lord Evermore]

Well, if they were arranged on racks surrounding the users head they might be an issue...

However just a window in a case isn't going to be a problem. The rest of the steel or aluminum frame and housing controls the EMI pretty well. They have to, otherwise the system could interfere with other devices. Remember the "this device may not interfere with any other device and has to accept any interference from anything else" clause in the motherboard manual? The case frame should normally be grounded by the PSU; if not, don't touch the damn thing!

 

[downhiller80]

Sorry I wasn't clear: I'm not worried aboutharm to myself, but (like that quote you gave) the effects this radiation could have on other electrical equipment around.

 

[jackschmittusa]

Yes there is a potential problem. That is why clear cases come with the caveat "for demonstration or educational use only". There are even blank plates in empty external drive bays to complete the Faraday Cage that a metallic case functions as.

Lord Evermore
The "may not interfere - etc." reference just means that the FCC can make you shut the machine off if it interferes with someone else's gear.

 

[Lord Evermore]

Well that's what I meant. The case makers don't want you to have to be told by the FCC to shut it down, so a proper case design would control the EMI. I would assume that the usual plexiglass windows aren't large enough to really cause too much of a problem, and other devices with shielding would be well enough protected if they faced the plexi window.

 

[ElFenix]

Originally posted by: Lord Evermore
Well, if they were arranged on racks surrounding the users head they might be an issue...

However just a window in a case isn't going to be a problem. The rest of the steel or aluminum frame and housing controls the EMI pretty well. They have to, otherwise the system could interfere with other devices. Remember the "this device may not interfere with any other device and has to accept any interference from anything else" clause in the motherboard manual? The case frame should normally be grounded by the PSU; if not, don't touch the damn thing!

interestingly enough that clause doesn't apply to home built stuff, which is why case windows and things are even legal

 

[Lord Evermore]

But wouldn't it affect cases people buy pre-modded?

 

[jackschmittusa]

It doesn't matter who builds it. The FCC regs say that you cannot operate an RF emitter that interferes with other people's electric/electronic devices. The first remedy is to advise the the owner of the offending equipment of the interference and afford them the opportunity to correct the problem if it is an otherwise legal device. If this remedy fails, the FCC can force you to cease using the device. This is seldom a problem with computers, but it is a potential problem which some manufacturers do a CYA with a disclaimer.

 

[Baileybbk]

P4s do spit out a ton of EMI.
I know it does interfere with some RF remotes to a degree.

 

[ElFenix]

oops, may have read 15.23 wrong

Sec. 15.23 Home-built devices.

(a) Equipment authorization is not required for devices that are not
marketed, are not constructed from a kit, and are built in quantities of
five or less for personal use.
(b) It is recognized that the individual builder of home-built
equipment may not possess the means to perform the measurements for
determining compliance with the regulations. In this case, the builder
is expected to employ good engineering practices to meet the specified
technical standards to the greatest extent practicable. The provisions
of Sec. 15.5 apply to this equipment.

 

[alkemyst]

The way the FCC works is:

If you aren't causing problems to commercial clients - you are not a problem.

If you are causing problems to commercial clients - you will be found and shut down...perhaps (but not always) prosecuted.

Usually the only ones that get handcuffs are the ones playing hard to get (pirate radio mostly).