General > General Technical Chat
Sick of ridiculous KVL infighting
<< < (12/15) > >>
SandyCox:
I fully agree, but this thread is about KVL.
RoGeorge:

--- Quote from: snarkysparky on January 15, 2022, 02:47:17 pm ---Aren't we talking about a completely static situation.

--- End quote ---

No, there is nothing static in Lewin's paradox.

He said:  I'm gonna show you how two voltmeters connected in parallel can indicate two different voltages.

And everybody was, "yeah right, maybe if one is defective, you are trolling us, right?".  And then Lewin said something like:  "you know what, even more, I'm gonna make one show +0.9V, and the other show -0.1V, both in parallel, how about that, do you believe me?".  And everybody was:  "chill down professor, you must be drunk, or something".

Then the professor cobbles up a circuit with 2 voltmeters in parallel, and "bang!" he released a full blown EMP (Electro-Magnetic Pulse) in the middle of his circuit.  And one voltmeter goes +0.9V, the other goes -0.1V, just like he predicted, yet with both voltmeters connected in parallel.

And the professor is: "told, you!", and everybody else was:  :o
Then after a second, "wait a minute, you weren't suppose to do that!" (as in, we all assumed a static situation, or else said a conservative field).

Well, "assumption is the mother of all fuck-ups", I never said it was static, and my point is one of the most glorified of yours EE rules doesn't hold in some very particular situations, like I just shown you with my clever circuit and this EMP, or else said instead EMP, a non-conservative field for the most pedantic, sais the professor.

Well, the professor never actually said all those words, that was just my artistic rendering of how the whole debate started, technically.

-----------------------

From here on, even more human feelings and emotions are thrown into the game, electricians and engineers saying "my rules you point out as limited/sometimes wrong are working just fine for me, and I have my ways to deal with that particular EMP you showed, we use induced voltage in the probing wires instead", and the professor said "but that really is because your rule doesn't hold for non-conservative fields", and so on.

From here, each side gets more and more stubborn into its own interpretation, and bang!, 40 pages of fights on EEVblog only, and countless other debates elsewhere!  :rant:

 ;D



See for yourself at minute 50:50 (and those experimental results are not coming out of nowhere, it was all explained how something like that is possible, just watch the lecture(s) preceding the minute 50:50 demo):

8.02x - Lect 16 - Electromagnetic Induction, Faraday's Law, Lenz Law, SUPER DEMO
Lectures by Walter Lewin. They will make you ♥ Physics.
Simon:

--- Quote from: instrumental on January 14, 2022, 04:10:39 pm ---
Carrying that mentality forward, I've seen things go wrong in industry because people ignore this -- if you forget about fields, you forget that you shouldn't route over splits in ground planes (or, really, split ground planes without rationale -- but that's a whole different religious argument). I worked on a receiver board for a LiDAR on an upcoming lunar mission and the receiver is borked for this reason (SPI bus routed over a GND split near the signal path) -- needs substantial, costly, time-consuming redesign and respin, complicated by the fact that the designer doesn't understand the issue and won't concede that it's a fields problem (despite every fingerprint being there, from qualitative EMC to being able to measure the SCLK signal rising edge on the TIA output). Forget about fields and you'll never be able to solve many of the noise issues you're dealing with -- and don't hold any hope for understanding why your boards have failed EMC.

So, I put it to you -- are we educating new engineers right? Are we motivating the issues at hand well, and are we giving concise and intuitive explanations? If we're triggering holy wars then the explanations at hand are not good enough, and we need to do better. As to what those might look like? Well, I've no idea what's intuitive to newcomers of the field; I've been at this too long. What helps? How do we avoid more of the kind of 39-page inane fighting on this forum, and between YouTube electronics education superstars?

--- End quote ---

You don't need a degree in physics to know that you should not route a trace from one ground plane to another, this is because you don't need to know down to the atomic level why it's a bad idea, at a basic level you just need to know not to do it, a slightly better engineer will know the verbal reasoning but won't need to worry about the math. It is the physicists job to tell you the math detail but for the purposes of designing a PCB that's irrelevant, because as a good engineer you know not to do it.

i have no idea about fields, but I put items including a SMPS through military EMC testing successfully, no physics knowledge required, I'm just a good engineer. If you asked to to prove down to the math why my method worked I will tell you to consult a physicist. I can tell you broadly what is going on but I won't be calculating the rf emissions for you. No one sits down and makes calculations to that level when they design for EMC, they learn what works and what does not and hopefully get mentored by anther experienced engineer. Theoretical evaluation of an EMC scenario is far more complicated than designing with well informed instinct based on intuition and experience. That is the difference between engineers and physicists.

So as he is the ultimate physicist why did he do a demo to disprove a theory but not explain that the theory was not meant to hold at this level and then explain what was going on. He just seemed to disprove someone with no explanation himself.
PlainName:

--- Quote ---at a basic level you just need to know not to do it
--- End quote ---

I think this is what distinguishes, say, a script kiddy from a programmer. Anyone can follow rules, but knowing why you follow them allows you to apply them properly and appropriately (and, sometimes, not to). As they say, "Rules are for the obedience of fools and the guidance of wise men."
Simon:

--- Quote from: dunkemhigh on January 16, 2022, 11:15:47 am ---
--- Quote ---at a basic level you just need to know not to do it
--- End quote ---

I think this is what distinguishes, say, a script kiddy from a programmer. Anyone can follow rules, but knowing why you follow them allows you to apply them properly and appropriately (and, sometimes, not to). As they say, "Rules are for the obedience of fools and the guidance of wise men."


--- End quote ---

Knowing why is different to doing the mathematical proof about it. If I already understand enough to know that it is not a thing I should do. Do I need to to the theoretical math and prove it ? no I don't, because I know enough to know broadly that the outcome is a fail.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod