Re: Hand waving and hand wringing.
I'm trying to learn something, Fred. But how can I learn something when you present stuff which seems to be at odds with other stuff you present? I've asked several times for you to explain the seeming conflicts yet instead of answering and clearing up the confusion, you just launch into personal attacks.
So I don't see that it's a matter of my being incapable of learning anything as much as your being incapable of teaching anything. Or at the very least unwilling to. What sort of teacher is it who can say nothing more than "read the book" and never answer any questions about what's in the book?
se
Fred Dieckmann said:
I'm trying to learn something, Fred. But how can I learn something when you present stuff which seems to be at odds with other stuff you present? I've asked several times for you to explain the seeming conflicts yet instead of answering and clearing up the confusion, you just launch into personal attacks.
So I don't see that it's a matter of my being incapable of learning anything as much as your being incapable of teaching anything. Or at the very least unwilling to. What sort of teacher is it who can say nothing more than "read the book" and never answer any questions about what's in the book?
se
Fred, Frank, Steve, give it a rest. To the extent you're discussing the issues, carry on. To the extent you're discussing one another, cut it out.
metalman, 1/137, I'd like to see the derivation myself. IIRC from my dim Jackson days, the solution was not a simple one. It clearly reduces to the plane formula as the skin depth gets small with respect to the wire diameter, but when they're of similar magnitudes, I don't think it looks at all the same.
Doing (gasp!) measurements, one sees an increase in Z versus frequency which clearly contains the skin effect term, along with the geometric inductance. But doing a quick check of my own speaker cables (12 gauge, rather coarse stranding, a suspiciously bright orange jacket, totally nonexotic, about 3 meters, Ace Hardware brand), the attenuation at 20 kHz with a resistor at the end is on the order of 0.1-0.2 dB compared to 1 kHz. That's in line with the behavior of zip cord presented in the somewhat hilarious Ben Duncan article in Stereophile a few years back. Even if that attenuation were all skin effect (it's not), I am skeptical regarding its audibility.
Doing (gasp!) measurements, one sees an increase in Z versus frequency which clearly contains the skin effect term, along with the geometric inductance. But doing a quick check of my own speaker cables (12 gauge, rather coarse stranding, a suspiciously bright orange jacket, totally nonexotic, about 3 meters, Ace Hardware brand), the attenuation at 20 kHz with a resistor at the end is on the order of 0.1-0.2 dB compared to 1 kHz. That's in line with the behavior of zip cord presented in the somewhat hilarious Ben Duncan article in Stereophile a few years back. Even if that attenuation were all skin effect (it's not), I am skeptical regarding its audibility.
delta<<R
Everything I have worked with in the dim dark past was always with delta <<R....
I quickly googled looking for something more general looking at the "wire problem" but wasn't able to find anything of use.
I suspect that you end up with a mass of special functions in the infinite cylinder case....maybe bessel functions?
Maybe I will attempt it but I am not sure I have the attention span anymore...
but then again..to a good local approximation...the world is flat!
rt
Everything I have worked with in the dim dark past was always with delta <<R....
I quickly googled looking for something more general looking at the "wire problem" but wasn't able to find anything of use.
I suspect that you end up with a mass of special functions in the infinite cylinder case....maybe bessel functions?
Maybe I will attempt it but I am not sure I have the attention span anymore...
but then again..to a good local approximation...the world is flat!
rt
Steve Eddy said:
I notice you didn't say we can't discuss you.
So tell us, SY, are women really more attracted to men in uniform?
se
Go right ahead. Just remember, I can edit your posts, and you don't want to have people quoting you about that incident with the gerbil.
My wife likes me to bring my diploma to bed. "Ooooh, honey, when you talk about Bessel Functions of the Second Kind, it makes me swoon!"
Fred, are these words your words, Ott's words, or someone else's words?
Noise induced by varying magnetic fields will be differential and not rejected by a balanced circuit, which rejects common mode noise.
Reason I ask is that I'm going to call Whitlock on Monday and run this by him and want to give the quote proper attribution.
se
Noise induced by varying magnetic fields will be differential and not rejected by a balanced circuit, which rejects common mode noise.
Reason I ask is that I'm going to call Whitlock on Monday and run this by him and want to give the quote proper attribution.
se
As Sy said........
Noise induced by varying magnetic fields will be differential and not rejected by a balanced circuit, which rejects common mode noise.
"Fred, are these words your words, Ott's words, or someone else's words?"
As Sy said we are to deal with the technical issues not personality issues. Why not run the statement in question by Mr. Whitlock and see what he thinks of the premise instead worrying about who said it. The statement should stand on it's own merit rather than who said it. If it is Mr. Whitlock's quote, you should give him proper credit of course. I would hope that you would call him to discuss the topic and not waste his time trying to find the source of a quote. Tell him you read it on the Internet and wondered if it was true.
"A balanced interface can reject any interference — whether because of ground voltage differences, magnetic fields, or electric fields — as long as that interference produces identical voltages, with respect to ground, on each of the signal lines. Because they're common to both inputs, these identical voltages are referred to as the common-mode voltage."
"— as long as that interference produces identical voltages, with respect to ground, on each of the signal lines."
Ask in particular what this qualifier means.
I believe the above quote is Mr. Whitlock's. I would ask him if this means that balanced interfaces only reject noise as long is it common mode noise. Ask him about it's rejection of differential noise and if there should difference between parallel conductors and twisted pairs for generation of noise from interference from time varying magnetic fields. You can quote Mr. Whitlock on his answer to this since I believe this is topic of debate, is it not? Focus on the issues as Sy advised.
Noise induced by varying magnetic fields will be differential and not rejected by a balanced circuit, which rejects common mode noise.
"Fred, are these words your words, Ott's words, or someone else's words?"
As Sy said we are to deal with the technical issues not personality issues. Why not run the statement in question by Mr. Whitlock and see what he thinks of the premise instead worrying about who said it. The statement should stand on it's own merit rather than who said it. If it is Mr. Whitlock's quote, you should give him proper credit of course. I would hope that you would call him to discuss the topic and not waste his time trying to find the source of a quote. Tell him you read it on the Internet and wondered if it was true.
"A balanced interface can reject any interference — whether because of ground voltage differences, magnetic fields, or electric fields — as long as that interference produces identical voltages, with respect to ground, on each of the signal lines. Because they're common to both inputs, these identical voltages are referred to as the common-mode voltage."
"— as long as that interference produces identical voltages, with respect to ground, on each of the signal lines."
Ask in particular what this qualifier means.
I believe the above quote is Mr. Whitlock's. I would ask him if this means that balanced interfaces only reject noise as long is it common mode noise. Ask him about it's rejection of differential noise and if there should difference between parallel conductors and twisted pairs for generation of noise from interference from time varying magnetic fields. You can quote Mr. Whitlock on his answer to this since I believe this is topic of debate, is it not? Focus on the issues as Sy advised.
Sch3mat1c said:Huh....
Been thinkin...
Take a piece of copper wire, and a piece of resistive stuff, both the same dimensions. One naturally has more resistance per length than the other.
Now, measure at HF. Due to skin effect, the copper wire may not be fully utilized, however the resistance wire will have a deeper skin, thus more of it will be used.
I was thinking, obviously it depends on just how much deeper it runs, but would the resistance wire not be more conductive than the Cu at HF?
And BTW, why does it seem to be so very hard to find a good skin effect formula? If there is, why hasn't it been posted here...? I don't see why someone can't come up with a very accurate formula relating dimensions, frequency, resistance and so on?
Tim
Skin effect in metals: a short answer.
Because of internal flux, an internal filament of current in a metal at the center of the wire is linked by more flux and therefore has more reactance than a filament of current at the surface. Current seeks the lowest impedance path and therefore tends to flow at the surface.
The depth of penetration can be defined as Delta=Squareroot(2/(omega*mu)) where omega is the freq of the signal and mu is the magnetic permeability of the wire material.
Does this help?
Source: John D Ryder, PhD, Engineering Electronics with Industrial Applications and Control, McGraww Hill, 1957
Jan Didden
janneman said:
Hopefully.
You did the best job so far in citing a succint, lucid and effective explanation of the physical meaning of skin effect.
After all these crap sandwiches it was very refreshing.
Goddamn! people do love to show off! I wonder how many people start writing out solutions of second order diff. eq. when designing audio gear.
