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Does a capacitor charges smooth, or in stairs?
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rhb:

--- Quote from: StillTrying on June 07, 2020, 02:32:48 pm ---If I use 2 1/2 meters of coax as the capacitor I can see the steps. LOL
Charged and discharged through a 390R resistor.

--- End quote ---

Very nice demonstration.

If the scope had a good step response it would be a very neat step approximation of the exponentials.  With a multisection trombone line you could make the steps smaller and smaller until they disappeared.

Rather like the fundamental theorem of calculus.

Would you post a schematic of the setup you used?  I'd like to try doing it with my 1 GHz Tek 7104 analog scope and one of Leo Bodnar's <40 ps edge pulsers.  Being traditional Tek it has a good step response even if it's out of adjustment.

Have Fun!
Reg
jmelson:

--- Quote from: Nominal Animal on June 07, 2020, 06:45:21 am ---You can extend this into the capacitors themselves, if you model a long skinny capacitor charged or discharged at one end, in which case the capacitor itself becomes part of the circuit – transmission line, really.

--- End quote ---
AHA!  I know this one, that's a coaxial cable!  And, I've sure studied those with TDR techniques to detect where the bad spot is, etc.

I've also seen "capacitor quakes".  We built a rig to detect neutrons, back in days of the Pons-Fleishman madness.  It had a bunch of He-3 detectors in a tub of paraffin moderator.  These detectors needed a 1500+ V bias, and then the signal was capacitively coupled to electronics.  When you turned on the bias, there were large pulses for several hours which slowly decreased in frequency.  This turned out to be the ceramic capacitor dielectric being squeezed by the electric field, and "creaking".  It made the whole setup very unreliable.

Jon
Jon
RoGeorge:

--- Quote from: jmelson on June 07, 2020, 05:56:39 pm ---It had a bunch of He-3 detectors...

--- End quote ---

Did you say Helium 3?!   :o



 ;D
Nominal Animal:

--- Quote from: RoGeorge on June 07, 2020, 04:44:07 pm ---I know nobody is booing
--- End quote ---
Good, because even if it is not a good model for a capacitor per se, it is/can be very useful model for a capacitor in a circuit.


--- Quote from: RoGeorge on June 07, 2020, 04:44:07 pm ---maybe it's OK to make things easy to comprehend, at first, then unlearn that later in order to achieve greater levels of detail
--- End quote ---
Very well could be; I don't know.  All I know is that some people I've tried to help learn struggle hard with that unlearning.  Best case scenario, in my opinion (and the core of that "rant") is to make sure your explanation is rooted in a verifiable random-access context.


--- Quote from: RoGeorge on June 07, 2020, 04:44:07 pm ---even if the jump to the most complex explanation we have for now would be comprehensible, never forget that there is no ultimate explanation.
--- End quote ---
Very true, and that makes it even more important to teach kids critical thinking.  And to not shy away from opposing viewpoints, but to explore them, to see what the core or basis for that viewpoint is.

Me, I'm often wrong.  Understanding what others base their opinions on, helps me evaluate the reliability of my own.  It being just the current working set of assumptions and opinions, after all.


--- Quote from: RoGeorge on June 07, 2020, 04:44:07 pm ---my respect for most of the quantum theory (and other latest century physics) might be pretty low
--- End quote ---
I'm pretty jaded at anything 'nano' myself: it's typically just a buzzword.

QM simulators, like VASP (Vienna Ab Initio Simulation Package) are typically based on density functional theory, and really just model the electrons only, using Schrödinger equation.  Using just the theoretical models of how electrons (or charges) interact, the minimum energy configurations these simulators find seem to describe actual molecules and lattices very accurately.

Classical potential models treat each atom as a separate particle, with interactions between particles described using a potential function – typically between two, three, or four particles; metals (except some like chromium) typically work well with just two, biomolecules use models with three or four.  Forces are derived from the potential function (literally, hah!), as the negated gradient of the total potential is the force acting on a particle.  These usually have an algebraic form derived from how the outer electrons in these atoms interact, with constants fitted to real-world measurements.

Water is surprisingly one of the nastiest to model. 

Currently, the simulators' core structure is straight off the seventies, except with CUDA acceleration bolted on.  That's what I'd like to improve on, making it easier for non-programmer physicists to efficiently try out new potential models, parallelize the simulations better, and allow mixing particle trajectory simulations with Monte Carlo methods (so that long-term equilibrium states can be found more efficiently, following some kind of simulated event or process, without switching simulators).  Oh, and to make Monte Carlo simulations distribute/parallelize better.  I like doing that kind of work, and watch and see what others can discover using those tools.
 

--- Quote from: RoGeorge on June 07, 2020, 04:44:07 pm ---Can your software run a simulation where electrons are replaced by muons?
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Not mine, but I think it should be doable in VASP or some of the other Ab Initio ones, by modifying electron mass; that should "pull" the muon orbitals much closer to the nucleus, so the modifications should be easy to verify with a muonic hydrogen atom.  Pity VASP isn't open source.  Oh darn, Dalton is since 2017, and I hadn't noticed!  I'm out of touch.


--- Quote from: jmelson on June 07, 2020, 05:56:39 pm ---I've also seen "capacitor quakes".
--- End quote ---
What I'd like to know, is how long did it take to discover the culprit!

I've always had a soft spot for LENR, just because it would be so useful if it'd work.. although we're starting to have really interesting SMRs, actually.  Pity the public does not realize coal power releases more radioactive particles into the atmosphere than nuclear power does, even including all past accidents.

For a hobby project, I'm trying to help put together a sensor suite for a fusor; specifically, a robust subsystem for temperature, pressure, etc. monitoring.  Simple, really, except that it should be maintainable and understandable by physicists with minimal electronics or programming background; and I just don't believe cobbling together something on top of Labview is a good idea.  It's always the human issues that make things difficult!  ;D
Labrat101:
Hi all
I am running this experiment on 320cm (3mtr 20) satellite cable which has a capacitance of 0.184nf .
Cat 5 series 59 , 20AWG .
Using the same more less setup as in our friends "StillTrying"  picture I could reproduce this image.
..
I stopped and thought for a while . this can't be right .. and I had this vision of Dave Johns whacking me with a baseball bat.  :palm:
So I ran some test on my HP Agilent scope . Ran a frequency scan to find the tuned frequency of this cable. with a sine wave. these steps are there .. Miss match!! change the resistor to match the cable . and ran a 50ns pulse . I got a square wave back.. the staircase vanished .
What you are seeing is the reflected pulse harmonics back adjusting the frequency up or down adds more steps .
 From what I am seeing its not a capacitive charge in a staircase, but a miss matched independence .
When the cable is matched to the scope .also the probes have a capacitance my one is 13pf  has to be add to the equation .

Also on our  friends  ''StillTrying'' scope picture had ringing on his pulse which would also be reflected ..
 I am not knocking your work or the scope picture it was good .  :-+
I would like to see someone else's work on this ..

I started with 390 ohm in series with the centre core and the screen to ground . 1 probe 200mhz @x10 on core after the 390 ohm . Set 5Mhz pulse  @ 5v  . 1st attempt .
also tried low freq @ 100khz @ 2v  , 10mhz  @ 5v , 12.5mhz @ 5v , 20mhz @ 5v , & 25mhz @ 5v  pulse
I also put another scope at the end of the cable ..
I only go this staircase affect when the cable was Not match to the scope .  :-+

I am awaiting for some new parts for my function Generator so I can reinstall the OCXO  and have 0.02 PPb  ;D
 at the moment its only 200ppm but good enough for this test .
 
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