What is EMI shielding?

[NervousNovice]

What does it mean when they say a computer case has "good EMI shielding" ? How does it affect the pc itself (including its performance) ?

 

[Schadenfroh]

Electro Magnetic Interference

 

[NervousNovice]

Hmm....what is that? @__@

 

[corkyg]

As Schadenfroh says, EMI stands for Electro Magentic Interference. When a case is well shielded, it uses good grounding and shielding materials to prevent EMI from causing problems. Shielding can be grounding, screening, and simply positioning.Some electrical engineers look upon it as somewhat akin to black magic.

Sometimes wiring harnesses which place cables in a physically parallel bundle can create spurious emissions due to additive EMI. I have seen the cure simply be to jumble up the wires/cables. Sometimes neatness causes EMI. It is wierd.

 

[corkyg]

As Schadenfroh says, EMI stands for Electro Magentic Interference. When a case is well shielded, it uses good grounding and shielding materials to prevent EMI from causing problems. Shielding can be grounding, screening, and simply positioning.Some electrical engineers look upon it as somewhat akin to black magic.

Sometimes wiring harnesses which place cables in a physically parallel bundle can create spurious emissions due to additive EMI. I have seen the cure simply be to jumble up the wires/cables. Sometimes neatness causes EMI. It is wierd.

 

[dkozloski]

It's important to remember that EMI shielding has nothing whatever to do with improving the performance of your computer but is to keep from affecting radio and television reception in your area.

 

[wizdum]

Originally posted by: dkozloski
It's important to remember that EMI shielding has nothing whatever to do with improving the performance of your computer but is to keep from affecting radio and television reception in your area.

Uhhhhh no it isn't.

 

[Cerb]

Originally posted by: wizdum

Originally posted by: dkozloski

It's important to remember that EMI shielding has nothing whatever to do with improving the performance of your computer but is to keep from affecting radio and television reception in your area.

Uhhhhh no it isn't.

Uh, yes it is.
Listen to AM radio and come down my driveway. It will be nothing but static by the time you stop. Guess what's real close? 6 open-case PCs. If you're 20ft or so away from the den, all is good. If the power is out, all is fine. When the UPS needed new batteries (and so nothing was left on 24/7 for a week) all was fine.

 

[wizdum]

I had an MSI motherboard that would shut off if I barely touched it. I read the manual and it said it was because of EMI. So wouldn't EMI be more affecting to the actual PC?

 

[thorin]

Originally posted by: dkozloski
It's important to remember that EMI shielding has nothing whatever to do with improving the performance of your computer but is to keep from affecting radio and television reception in your area.

And vice versa. The EMI from your sys can affect your other electronics.

Thorin

 

[gsellis]

Originally posted by: wizdum

Originally posted by: dkozloski

It's important to remember that EMI shielding has nothing whatever to do with improving the performance of your computer but is to keep from affecting radio and television reception in your area.

Uhhhhh no it isn't.

2nd... uhhhh yeah.

FCC Class A vs Class B can be all about the shielding. It works both ways though, reduces noise outbound and reduces interference inbound.

 

[dkozloski]

I should have added a caveat. The FCC doesn't care if your computer works or not as long as it doesn't cause interference problems for someone else. Except in rare cases, EMI does not affect the operation of digital equipment such as computers because internal signal levels are so high compared to possible interference. EMI from your computer can cause noise in your sound system, your radio, and noise and picture problems in your TV. It is more likely that if touching the innards of your computer causes problems that it is body capacitance affecting the propogation of signals in the internal circuits rather than the introduction of noise from an outside source. Internally, noise from the CPU and memory circuits can get into your sound card but the case shielding does nothing for this. Here you must tinker with wire routing and shielding and component separation.

 

[corkyg]

Correct! And also cell phones in some frequency bands.

 

[wizdum]

Originally posted by: Cerb

Originally posted by: wizdum

Originally posted by: dkozloski

It's important to remember that EMI shielding has nothing whatever to do with improving the performance of your computer but is to keep from affecting radio and television reception in your area.

Uhhhhh no it isn't.

Uh, yes it is.
Listen to AM radio and come down my driveway. It will be nothing but static by the time you stop. Guess what's real close? 6 open-case PCs. If you're 20ft or so away from the den, all is good. If the power is out, all is fine. When the UPS needed new batteries (and so nothing was left on 24/7 for a week) all was fine.

I stand corrected! Pardon my ignorance.