Grey metal type ring in computer case? 4

[CraigHappy]

Hi

This may be a really silly question, but please can anyone tell me what the metal type ring with the computer case cables wrapped around it actually does?

I've seen them in quite a few computers, but never knew what they were for?

Many thanks

Craig.

 

[LawnBoy]

Those are toroid chokes. They are used to impede high frequency noise on the line. Basically, a 'line-filter'.


"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[gbaughma]

Exactly right, LawnBoy. Have a star.



Just my 2¢
-Cole's Law: Shredded cabbage

--Greg

http://parallel.tzo.com

 

[LawnBoy]

Haven't seen you around for a while Greg, glad you're back. Thx for the star!


"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[gbaughma]

Oh, I'm here every day. You're just so quick on the answers, you always beat me to 'em!

Keep up the good work.



Just my 2¢
-Cole's Law: Shredded cabbage

--Greg

http://parallel.tzo.com

 

[CraigHappy]

Many thanks for the quick and clear response!

Now I know!

Cheers

Craig.

 

[LawnBoy]

Glad to be of assistance.

"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[CraigHappy]

Just for rxtra info.

I have just found that these rings are also called -
"ferrite ring".

 

[edfair]

Not to pile on, but they don't have to be rings either, although that seems to be the most common.

The one that keyed this post was a set of parts that combined to surround a ribbon cable in a pass-thru arrangement. Assembled it was probably 1"by 2" by 1/2" thick with room for a 34 conductor ribbon to pass through it.

 

[electronicsfreak]

Im bumping this thread as im curious to know more about this. What examples of high frequency does this filter? Reason I ask is I have not heard any noises on my sound cards that ive used. Well except the pop if I shut off the computer. Just was curious to know more about this. So if you could explain more that would be nice.

Yes I do understand high and low pass filters lol. Im a car audio nut, so I understand that. Anyway just when you can explain more detail on noises and other things if you can. Hungry mind here wanting to learn lol

There is a point in wisdom and knowledge that when you reach it, you exceed what is considered possible - Jason Schoon

 

[gbaughma]

Ferrite rings / chokes have been used for years and years.

The concept is two-fold (from my understanding of being a Ham Radio operator)

1 - Higher frequencies have a problem making the "turn" around a tight loop... the frequency actually leaks out the turn of the wire, kind of like if you were driving a car too fast to make a tight turn; the frequencies "go off the road" as it were.

2 - The ferrite (aka iron; ferrous) choke sets up a small magnetic field (since you are, in fact, wrapping wires around a ferrous object much the same way a transformer does) which helps to reinforce the lower frequencies while allowing the higher ones to bleed off.

The ferrite rings are essentially used to filter off induced noise from surrounding RF fields. I have them on USB cables here at work as well, which helps cut down on interference.



Just my 2¢
-Cole's Law: Shredded cabbage

--Greg

http://parallel.tzo.com

 

[gbaughma]

Ahh... I should have looked at this while I was typing... here's a good wiki article:

http://en.wikipedia.org/wiki/Ferrite_ring

Just my 2¢
-Cole's Law: Shredded cabbage

--Greg

http://parallel.tzo.com

 

[LawnBoy]

I'll take a stab at explaining the theory, I'm sure Greg and others will keep me honest

If you take a wire and run a voltage (say, 12 vdc) through it to a load, the current flow will produce a small magnetic field around the entire length of the wire. If you now take that wire and wrap it around a pencil a few times you will have created a coil, and the area around this coil will have a larger magnetic field around it. If you then remove the pencil from the center of that coil, and replace it with some kind of ferrous (magnetic) material (ferrite works very well) you will now have a Much Larger magnetic field around the coil.

This is what you're doing with a choke. You're creating a larger magnetic field around one spot on the wire(s).

As it happens, a magnetic field likes to stay stable. It is reluctant to change. The stronger the field, the more reluctant it is to change.

Now lets say that some high frequency noise gets on our wire(s). This signal is going to increase the magnetic field when it is positive, and subtract from the field when it is negative. And it will be successful, until it hits the (relatively) large magnetic field created by the choke. This larger, stronger field is much more reluctant to fluctuate up and down, thereby blocking (attenuating) the high frequency noise.

That's the basic principle. I've ignored a lot of details in trying to keep this simple, so please be gentle...

<dons asbestos suit>


"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[electronicsfreak]

Now lets say that some high frequency noise gets on our wire(s). This signal is going to increase the magnetic field when it is positive, and subtract from the field when it is negative. And it will be successful, until it hits the (relatively) large magnetic field created by the choke. This larger, stronger field is much more reluctant to fluctuate up and down, thereby blocking (attenuating) the high frequency noise.


That is what I wanted to know. I understand the rest lol. Thanks! makes sense

There is a point in wisdom and knowledge that when you reach it, you exceed what is considered possible - Jason Schoon