I meant to say ... "but I'm not totally sure..." ----- Original Message ----- From: "Cuchulain" <jlipsius@xxxxxxxxxxx> To: <dp@xxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> Sent: Sunday, August 07, 2005 8:41 PM Subject: [SI-LIST] Re: Current Flow > I think it's about a transgalactic teletransporter prototype and supporting > instruments to measure charge flux in any volume of the > galaxy... but don't I'm totally sure > :-) > > > ----- Original Message ----- > From: "Dimiter Popoff" <dp@xxxxxxxxxxx> > To: <si-list@xxxxxxxxxxxxx> > Sent: Friday, August 05, 2005 4:11 PM > Subject: [SI-LIST] Re: Current Flow > > > > Is'nt the physics about electricity taught in high school? > > Electric field spreads at the speed of light, causing electron > > motion, which we call current flow, which is responsible for > > magnetic field, which while changing creates electric field etc. etc. ??? > > Unless the thread is about teaching kids <16 how to design > > boards, I don't quite get what this is about. > > > > Dimiter > > > > ------------------------------------------------------ > > Dimiter Popoff Transgalactic Instruments > > > > http://www.tgi-sci.com > > ------------------------------------------------------ > > > > > > > > > > -------Original Message------- > > > From: steve weir <weirsi@xxxxxxxxxx> > > > Subject: [SI-LIST] Re: Current Flow > > > Sent: Aug 06 '05 01:46 > > > > > > Doug, as long as we take the view of electrons on one side of the path > > > moving at some finite velocity and as a consequence causing other > > > electrons > > > to later move along the return path, we are at an impasse with > > > reality. There is no such delay between signal and return. Both sides > > > propagate in unison because they are both the observable result of the > > > propagating wave front. Signal <=> Return. Return <=> Signal. > > > > > > Regards, > > > > > > > > > Steve. > > > > > > At 03:05 PM 8/5/2005 -0700, Doug Brooks wrote: > > > >At 02:18 PM 8/5/2005, you wrote: > > > >>Doug, > > > >> > > > >>In the fluid model, we would see current propagate down the signal > > > >>conductor and then later back in the return lead would we not? > > > > > > > >That's why I said I didn't think "fluid" was the best descriptor. As I > > > >tried to point out the first time, electrons start flowing down the > > > line, > > > >onto the "plates" of the distributed capacitance, repelling electrons > > > >(like charges repel) from the other "plates" of the distributed > > > >capacitance, and back, completing the loop. As the first "plates" charge > > > >up, the current flows past them and charges the next "plates". By the > > > time > > > >the current gets to the end if the line, all the "plates" are charged > > > up, > > > >and the flow looks like a DC flow would look. This is exactly what > > > Figure > > > >7-19 in Bogatin's book is describing. You describe this from the > > > >standpoint of "waves". I can equally well (no better, no worse) describe > > > >it as electron flow. I don't see a difference and I don't see a problem. > > > > > > > >The "fluid flow" model breaks down because we can't envision fluid > > > >crossing between the plates of a capacitor. But electron flow CAN cross > > > >the plates of a capacitor because of the property that "like charges > > > repel > > > >each other." Electrons don't physically cross the space between the > > > >plates, but they build up on one side and repel those on the other, so > > > >that the same number of electrons return to the source as left it. > > > > > > > >Doug > > > > > > > > > > > > > > > >>But in real life, we observe that current propagates in one polarity > > > from > > > >>the signal conductor portion of the wave guide, and simultaneously in > > > the > > > >>opposite polarity from the return conductor side of the wave guide. The > > > >>fluid flow model has problems both with time, and with the fact that > > > the > > > >>wave propagates down an infinitely long open transmission line just as > > > >>well as it does an end terminated line. In the open, or infinite length > > > >>line electrons never passed from one conductor to the other. > > > >> > > > >>How does a circular fluid flow analogy model this behavior? At the far > > > >>end of an open transmission line the conduction path is broken, the > > > fluid > > > >>has no contiguous path. > > > >> > > > >>We can agree that electrons in the conductors move in response to the > > > >>propagating fields, sic wave. But I have to reiterate that back at our > > > >>switch it is the fields interacting with the conductors that push on > > > >>those electrons you observe moving in the conductors. When the dv/dt > > > >>switches direction later in time, the charge will go the other way in > > > >>each conductor, but as far as charge between the two conductors: never > > > >>the twain shall meet. > > > >> > > > >>Regards, > > > >> > > > >> > > > >>Steve. > > > >> > > > >>At 02:12 PM 8/5/2005 -0700, Doug Brooks wrote: > > > >>>(I have changed the subject line to better represent what I think we > > > are > > > >>>talking about.) > > > >>> > > > >>>You raise an excellent example. Let me deal with the two points. > > > >>> > > > >>>1. I'm not sure I understand what you are getting at here. The focus > > > >>>should be at the point of the switch. > > > >>> > > > >>>2. I have introduced the problem in some of my transmission line > > > classes > > > >>>that deal with point 2. Assume that (a) there is a propagation time > > > for > > > >>>a signal, (b) current (i.e. electrons) flows in a closed loop, (c) > > > >>>current is constant everywhere in that loop ---- aren't these mutually > > > >>>exclusive conditions? The answer is no! The current flows down the > > > >>>transmission line from one side to the other through the distributed > > > >>>capacitance (as suggested in Bogatin's Figure 7-19). This is a current > > > >>>flow (i.e. electron flow) picture. If you want to call it a wave flow, > > > >>>well that's fine. But you can also describe it as current (electrons) > > > >>>flowing to the point of the distributed capacitance, repelling charge > > > >>>away from the other side of the capacitance back to the beginning of > > > the > > > >>>line, charging the capacitance up (with electrons) along the way. At > > > the > > > >>>steady state, current (electrons) is flowing in the DC loop we would > > > >>>expect. If we don't have a transmission line ---- well, we always have > > > >>>a transmission line of sorts. The question is whether it's ideal or > > > REAL > > > >>>crummy. There is always a characteristic impedance, even if it is only > > > >>>that of air. > > > >>> > > > >>>So the "fluid" analogy (I don't think that's the best descriptor) can > > > >>>deal with this issue perfectly fine. Likewise, it can deal with the > > > >>>crosstalk coupling issue equally as well. (I don't have a figure like > > > >>>Eric's in my book, but there is a very detailed illustration of how > > > >>>crosstalk coupling works in my book that doesn't need Maxwell and wave > > > >>>theory to understand.) > > > >>> > > > >>>So I don't see the difficulty here. > > > >>> > > > >>>Doug > > > >>> > > > >>> > > > >>> > > > >>> > > > >>> > > > >>>At 01:18 PM 8/5/2005, steve weir wrote: > > > >>>>Doug, in the fluid model, there are two misleading elements: > > > >>>> > > > >>>>1. The focus is on the source of EMF, sic the battery, > > > >>>>2. It implies a time lag between the foward current starting from > > > some > > > >>>>point and the matching return current closing that path. > > > >>>> > > > >>>>If we take the switch example you offered, one might imagine a couple > > > >>>>of different cases: > > > >>>> > > > >>>>a. The switch is located very close to one terminal of the battery > > > and > > > >>>>a say 300m wire connects it to the other through some load resistor. > > > >>>>b. The switch is located at the end of two 300m wires back to the > > > >>>>battery through some load resistor. > > > >>>> > > > >>>>Now, what will each the fluid analogy, and wave propagation tell us > > > >>>>about each case? Where does each model show the propagation beginning > > > >>>>and ending? How accurate is each? Which model can explain behavior > > > >>>>from virtual DC to any frequency we like? I don't think it's the > > > fluid > > > >>>>analogy. > > > >>>> > > > >>>>On a PCB with switching I/Os the time and distance scales have > > > changed > > > >>>>but not the behavior. What we have is in essence case b from > > > >>>>above. The wave emanates from the switches in our ICs, not from the > > > >>>>power supply. The wave model makes this clear, as it does the > > > >>>>propagation path. The wave model makes clear the critical point that > > > >>>>the return and forward currents propagate together. The fluid analogy > > > >>>>with its unidirectional emphasis fails us badly. > > > >>>> > > > >>>>Where has the fluid analogy brought us? How many times have you seen > > > >>>>people talk about bone-headed ideas like the PCB planes or bypass > > > >>>>capacitors supplying current to high speed edges, when the entire > > > edge > > > >>>>has completed long before the wave front through power pins can reach > > > >>>>significant charge in the planes, much less even reach the PWB bypass > > > >>>>caps? Yet this kind of junk mythology sadly makes its way into books > > > >>>>and other publications on a regular basis. I don't like it one bit. > > > >>>> > > > >>>>For my money, I find the fluid analogy terribly misleading, and a > > > >>>>source of much misunderstanding. One doesn't need to be able to > > > derive > > > >>>>Maxwell to understand wave propagation. I think that as Eric's book > > > >>>>demonstrates, most SI concepts are not that difficult to > > > >>>>understand. Even a dummy like me gets them from time to time. > > > >>>> > > > >>>>Regards, > > > >>>> > > > >>>> > > > >>>>Steve. > > > >>>>At 12:51 PM 8/5/2005 -0700, Doug Brooks wrote: > > > >>>>>A couple of people have interpreted my statement re "flow" of > > > >>>>>electrons as meaning electron drift. Let's kill that right now. > > > >>>>> > > > >>>>>One electron in = one electron out is the flow of electrons. One > > > >>>>>electron in = SAME electron out is electron drift --- not at all the > > > >>>>>same thing. > > > >>>>> > > > >>>>>Certainly I don't argue against Maxwell's equations. But I don't > > > argue > > > >>>>>against the fundamental definition of one amp of current either --- > > > >>>>>the flow of one coulomb of charge (6.25 x 10^18 electrons) across a > > > >>>>>surface in one second. I spend a lot of time with engineers (and > > > >>>>>technicians) who never took Maxwell's equations and didn't > > > understand > > > >>>>>them if they did. My goal has been to take our difficult SI concepts > > > >>>>>and explain them in terms that these "poor" people can understand. > > > To > > > >>>>>suggest that you can't explain what happens during planar > > > transitions > > > >>>>>without Maxwell's equations (I believe) is simply wrong. To say that > > > >>>>>the classical description of current can't explain the difference > > > >>>>>between DC and high frequency is also (I believe) flat wrong. To say > > > >>>>>that one description is "more accurate" than the other --- well I > > > >>>>>suggest that depends a lot on whose working with them! And while > > > >>>>>people have been misled by seminar leaders teaching without the > > > >>>>>benefit of Maxwell's equations, we all know seminar leaders whose > > > >>>>>ability to mislead wasn't one bit hampered by a thorough knowledge > > > of > > > >>>>>Maxwell's equations! > > > >>>>> > > > >>>>>Don't sell these more basic principles short when it comes to > > > >>>>>understanding what is happening on circuit boards. They can very > > > >>>>>effectively explain what is happening, and why one design approach > > > may > > > >>>>>be more effective than another depending on the important design > > > >>>>>considerations. Especially for all those board designers who have no > > > >>>>>knowledge of Maxwell and wave theory. > > > >>>>> > > > >>>>>Doug > > > >>>>> > > > >>>>> > > > >>>>> > > > >>>>> > > > >>>>>At 12:01 PM 8/5/2005, steve weir wrote: > > > >>>>>>Doug, well I am going to argue vehemently that until someone > > > repeals > > > >>>>>>Maxwell that the wave description is fundamentally more accurate > > > than the > > > >>>>>>fluid analogy. The E/M fields cause the electron drift in those > > > >>>>>>wires. From the time you closed the switch the changing E/M field > > > that > > > >>>>>>resulted propagated outward. Marconi found a useful purpose for > > > that > > > >>>>>>phenomenon. > > > >>>>>> > > > >>>>>>The fluid analogy is certainly easy to understand, but what is the > > > point > > > >>>>>>when it is so misleading? I can't tell you how many times otherwise > > > >>>>>>intelligent engineers that I have known have been thrown off > > > >>>>>>understanding > > > >>>>>>PCB wave guides, because they were intent on following the DC > > > current > > > >>>>>>loop > > > >>>>>>of the fluid analogy. > > > >>>>>> > > > >>>>>>Teaching the fluid analogy requires that we later break that > > > teaching > > > >>>>>>when > > > >>>>>>we want to explain what happens at significant frequencies. > > > Consider for > > > >>>>>>instance visualization of return current ( which is the original > > > subject > > > >>>>>>matter ) when we transition planes in a PCB. If we think about it > > > as a > > > >>>>>>fluid model we are easily misled into searching out a conduction > > > >>>>>>path. For > > > >>>>>>ready examples of this mass confusion, just look at some of the > > > >>>>>>discussions > > > >>>>>>on splitting-up grounds in the wrong ways for the wrong reasons, > > > with the > > > >>>>>>wrong results. But if we simply consider waves to begin with, then > > > the > > > >>>>>>behavior is easy enough to intuit out. > > > >>>>>> > > > >>>>>>Eric does a very nice job in his book explaining signal > > > propagation that > > > >>>>>>does not rely on the fluid analogy. I think his approach is very > > > >>>>>>accessible. > > > >>>>>> > > > >>>>>>Regards, > > > >>>>>> > > > >>>>>> > > > >>>>>>Steve > > > >>>>>>At 11:21 AM 8/5/2005 -0700, Doug Brooks wrote: > > > >>>>>> >With all due respect, Steve, if I have a battery connected to a > > > >>>>>> transistor > > > >>>>>> >through a switch, I can turn the transistor "on" and "off" with > > > the > > > >>>>>> >switch. That is easy to explain using the electron flow concept > > > >>>>>> (which I > > > >>>>>> >hesitate to call an analogy, it in fact describes the physics > > > >>>>>> involved). > > > >>>>>> > > > > >>>>>> >Is your description more complete AND also easier to understand? > > > >>>>>> > > > > >>>>>> >And if it is the frequency with which I "flip" the switch that > > > bothers > > > >>>>>> >you, that simply means that some of the parameters that were not > > > an > > > >>>>>> issue > > > >>>>>> >with slow "flipping" (inductance and capacitance, for example) > > > start > > > >>>>>> >becoming more of an issue with faster "flipping!" But the basic > > > >>>>>> nature of > > > >>>>>> >what is happening (in particular where the electrons are flowing) > > > >>>>>> is not > > > >>>>>> >changing, just speeding up. (How the electrons are flowing is > > > >>>>>> speeding up, > > > >>>>>> >the electrons themselves, of course, don't change speed!) > > > >>>>>> > > > > >>>>>> >Doug > > > >>>>>> > > > > >>>>>> > > > > >>>>>> > > > > >>>>>> >At 10:45 AM 8/5/2005, steve weir wrote: > > > >>>>>> >>Doug, I have some real heartburn with some of those > > > representations, > > > >>>>>> >>particularly the fluid analogy that speaks of current as the > > > flow of > > > >>>>>> >>electrons. When I grew up current was defined as time variation > > > of > > > >>>>>> >>electric flux. When an E/M field impinges a chunk of metal the > > > >>>>>> resulting > > > >>>>>> >>interaction concentrates the field forming a wave guide. All > > > >>>>>> practical > > > >>>>>> >>wave guides leak, be they a microstrip over a plane, a > > > stripline, or > > > >>>>>> >>whatever. Some, like a good semirigid coax leak only a little > > > tiny > > > >>>>>> >>bit. When they leak too much creating excessive disturbance in > > > >>>>>> nearby wave > > > >>>>>> >>guides, we have cross talk problems. I hope that this is what > > > you > > > >>>>>> were > > > >>>>>> >>trying to convey. > > > >>>>>> >> > > > >>>>>> >>Regards, > > > >>>>>> >> > > > >>>>>> >> > > > >>>>>> >>Steve. > > > >>>>>> >> > > > >>>>>> >>A > > > >>>>>> > > > > >>>>>> >Check out UltraCAD's new presentation videos and new skin effect > > > >>>>>> >calculator at http://www.ultracad.com > > > >>>>>> > > > > >>>>>> > > > >>>>>> > > > >>>>>>------------------------------------------------------------------ > > > >>>>>>To unsubscribe from si-list: > > > >>>>>>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject > > > field > > > >>>>>> > > > >>>>>>or to administer your membership from a web page, go to: > > > >>>>>>//www.freelists.org/webpage/si-list > > > >>>>>> > > > >>>>>>For help: > > > >>>>>>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > >>>>>> > > > >>>>>>List FAQ wiki page is located at: > > > >>>>>> http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > >>>>>> > > > >>>>>>List 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presentation videos and new skin effect > > > >calculator at http://www.ultracad.com > > > > > > > > > > > > > ------------------------------------------------------------------ > > > To unsubscribe from si-list: > > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > > > or to administer your membership from a web page, go to: > > > //www.freelists.org/webpage/si-list > > > > > > For help: > > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List FAQ wiki page is located at: > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > > List technical documents are available at: > > > http://www.si-list.org > > > > > > List archives are viewable at: > > > //www.freelists.org/archives/si-list > > > or at our remote archives: > > > http://groups.yahoo.com/group/si-list/messages > > > Old (prior to June 6, 2001) list archives are viewable at: > > > http://www.qsl.net/wb6tpu > > > > > > > > > > > -------Original Message------- > > 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