For a 1000' (304.8m) long 99.9% copper wire to have a resistance of 100 Ohm (at 20d C), the wire should have a cross section of 0.0512mm^2, a diameter of 0.255mm. That’s almost a 30AWG wire.
With 50V applied to the 100' wire (10 Ohm resistance), the current should be 5A.
This is too high a current for this wire size (0.86A is the load carrying capacity for 30AWG wiring in air, and not in a bundle, say 1A).
The wire will most probably open at some point.
If it will not open, it will start a circle of heating a lot and increasing it’s resistance, consequently dropping the current that passes through it, the resistance then will drop a bit, the current will increase again ect, ect.
I don’t have a 30AWG wire to run the test and Ed, the thermal calculation to find the equilibrium point is a pain to do.
What’s the final point for this question?
George
>Edit. I just read your previous post. You run the test. What was the wire temperature? And what was the current?
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> If it will not open, it will start a circle of heating
> a lot and increasing it’s resistance, consequently
> dropping the current that passes through it,
> the resistance then will drop a bit, the current
> will increase again ect, ect.
If that were true lightbulbs would pulsate .
For that type thermal oscillation there needs
to be a time lag someplace in the system .
> a lot and increasing it’s resistance, consequently
> dropping the current that passes through it,
> the resistance then will drop a bit, the current
> will increase again ect, ect.
If that were true lightbulbs would pulsate .
For that type thermal oscillation there needs
to be a time lag someplace in the system .
Scott,
I tried responding intelligently to this and it must have timed out and I lost all of my comments. Oh well, not going there again. I have a box of these devices from experimenting with them many years ago, seriously. If you would like to play with them I can send you a couple. I think I have one with the resistor removed as well as I was measuring its raw response.
It's funny, I've had a couple year hiatus from this forum and I decided to see what John was up to a week or two ago and dropped right back into a discussion that was going on prior to life dragging me away.
Mike
Their current oscillates initially, settling after a while to a steady state value.
There are a few thermal systems there too that impose their time constants on the R of the wire.
(If the next question is what are the consequences of all these thermal time constants, the answer will include ‘harmoniously distorted current waveform’)
If these questions were part of end of semester examinations , we would have 15 minutes max to formulate the answer in numbers, provided sufficient data plus an A4 sheet, pencil and eraser were provided. What’s going on here?
I would love Ed cranking up the voltage very slowly while monitoring the current to find out the current that will melt that 100 feet 30AWG wire.
Thus we will form an opinion over the safety margin embedded into the I max carrying value listed at the AWG tables.
And I will wait him to explain what was he up to with that question
George
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Yesterday I missed that post and Scott’s post
Why is it the PSU that will fail and not the wire?
What frequency is the signal?
Bandlimited measurement? Averaged measurements? How much?
What noise? Thermal of wire under test, test junction thermal differentials, EMI, cosmic?
Ed, it is far more productive to list the test conditions, spell the resulting numbers and have the discussion on these, rather that asking in this way.
We will have at least a grip over relative orders of magnitude.
Finish the picture and then let us decide together how much it worths.
Scott objects to the foggy wording not to the landscape.
It is known that I have great difficulties with the English language but the above quoted paragraph does not contain difficult words.
Alas, I read that paragraph 10 times before I was able to start assuming what you might want to convey.
Do you apply different meaning to ‘signal’ and ‘information’?
The term ‘charge interaction’ hides some dragons.
I am terminally infiltrated by Heaviside work but here I link to a modern paper on charge interaction .
http://www.physik.uni-augsburg.de/~schwab/paps/habil.pdf
Be assured that the subject of signal transport is one of my beloved wonders.
I would really enjoy your response with further explanations.
George
Why is it the PSU that will fail and not the wire?
What frequency is the signal?
Bandlimited measurement? Averaged measurements? How much?
What noise? Thermal of wire under test, test junction thermal differentials, EMI, cosmic?
Ed, it is far more productive to list the test conditions, spell the resulting numbers and have the discussion on these, rather that asking in this way.
We will have at least a grip over relative orders of magnitude.
Finish the picture and then let us decide together how much it worths.
Scott objects to the foggy wording not to the landscape.
It is known that I have great difficulties with the English language but the above quoted paragraph does not contain difficult words.
Alas, I read that paragraph 10 times before I was able to start assuming what you might want to convey.
Do you apply different meaning to ‘signal’ and ‘information’?
The term ‘charge interaction’ hides some dragons.
I am terminally infiltrated by Heaviside work but here I link to a modern paper on charge interaction .
http://www.physik.uni-augsburg.de/~schwab/paps/habil.pdf
Be assured that the subject of signal transport is one of my beloved wonders.
I would really enjoy your response with further explanations.
George
Your diverting.
Be more careful in providing technical information for a technical discussion.
You did the exact same thing when you had that inductance measurement that was orders of magnitude off. It took what, 3 or 4 posts to me to badger the information out of you that you weren't even using the right inductance test.
Be more careful. It pays in the long run, as more people will listen.
john
You are welcome Mr. Curl
I may have linked to this paper again.
It refers to as many mechanisms involved in Electron-Electron Interactions and Charge Transport as have been studied up today and this is the reason I brought it up now.
Please take the time to study the necessary conditions that pertain to each mode discussed (dimensions, temperature and other confiners).
Most of these modes have a meaning only in the microscopic and mesoscopic scale and only under very restraining specific conditions.
If you ask me and from what I can understand, in the macroscopic scale and under everyday conditions, it’s the diffusion mode that works.
I can claim that I have built at least 10 variations of miraculous devices or advanced interconnects and dress up my promotion brochure using selected paragraphs from that paper alone, for each one.
That could be very convincing for some of the potential customers but it would be a moral drift from my part to do this and the “advanced” products would be no better than plain common conductors.
George
I may have linked to this paper again.
It refers to as many mechanisms involved in Electron-Electron Interactions and Charge Transport as have been studied up today and this is the reason I brought it up now.
Please take the time to study the necessary conditions that pertain to each mode discussed (dimensions, temperature and other confiners).
Most of these modes have a meaning only in the microscopic and mesoscopic scale and only under very restraining specific conditions.
If you ask me and from what I can understand, in the macroscopic scale and under everyday conditions, it’s the diffusion mode that works.
I can claim that I have built at least 10 variations of miraculous devices or advanced interconnects and dress up my promotion brochure using selected paragraphs from that paper alone, for each one.
That could be very convincing for some of the potential customers but it would be a moral drift from my part to do this and the “advanced” products would be no better than plain common conductors.
George
Kliban cartoon, two panels. Upper panel: St. Peter at the pearly gates "Welcome to Heaven. Here's your harp." Lower panel: St. Nick at the eternal flames "Welcome to Hell. Here's your accordian."
Thanks,
Chris
From this interesting paper, we have to learn the following:
"Assume for example that there is a finite conductance of the interface which can be described by a tunneling Hamiltonian. It is well known that the Coulomb interaction plays an important role in the transport through tunnel junctions in a disordered system, since the density of states is reduced near the Fermi energy. This leads to a suppression of the tunnel conductance and to a nonlinear current voltage characteristics at low bias."
Practical consequence from this is, that for mechanical contacts (intercomponent connections) we must avoid micro-current signal transfer mode (high source output impedance and high receiver input impedance). The higher impedances - the more expensive higher quality interconnects are to be used. In order to skip from "snake oil games" - use 1...3K input volume pot, and source output impedance should be not more than hundreds Ohms.
From the clues- 10 Ohms and 1 pA. If the signal is 1 pA then the signal level would be 10 pV. To get 10 pV of noise on a 10 Ohm resistor it calculates to around .001 Hz bandwidth. However if the 10 pA are DC while the bandwidth is still valid usually the noise would not be looked at that way. For what its worth the best resolution on measuring DC voltage with commercial stuff is closer to 10 nV than 10 pV. However if you start looking at superconductor stuff there are ways to get there. JN would know a lot more. Is this an exercise in not quite enough info?
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