General > General Technical Chat
Admit your Brain lock
CatalinaWOW:
--- Quote from: Siwastaja on April 06, 2024, 08:56:47 am ---
--- Quote from: CatalinaWOW on April 06, 2024, 12:07:34 am ---In some sense these last couple of pages have been a variant of "Why can't we all just use the same words for everything."
--- End quote ---
No, it's the exact opposite: I am showing we must admit that we are NOT using the same words for everything, and we should not even try too hard for a totally universal symbol system as it's futile, but instead should try to concentrate on:
* Making communication simple and clear
* Explain and document the terms used
There is synergy between these two points: when you simplify, you reduce your own documentation task.
For example, a voltage produced by rotating permanent magnet motor does not care about line integral versus other types of integrals. It is just voltage, which you can measure with a multimeter, a simple one-dimensional scalar which changes as function of time. Therefore, a motor-generated voltage can be called voltage, and the term "electromotive force" or "line integral" does not need to appear in motor control theory at all.
Therefore, the explanation about what "motor-generated voltage" is, will be much shorter and easier to understand, than historical review of why electromotive force is called electromotive force and... well look at Sredni's reply. To really understand what he is saying I would need ten times more explanation, make myself a few cups of coffee, and look at it carefully. This is completely wasted time if I'm interested about the voltage that appears on the wires of a rotating permanent magnet motor, which is very relevant when I want to control the motor.
--- End quote ---
I agree, simple is good. But your example is a good one to start with. Do a thought experiment. Connect an ideal battery (no internal impedance) to an ideal DC motor (no friction, but it does have mass). Assuming the motor is not rotating at the start what happens over time? The motor accelerates until the back EMF (use that term for the moment, we'll get back to that) equals the battery voltage. The acceleration is proportional to the difference between the battery voltage and the back EMF. Where do you attach your voltmeter to measure the back EMF? You can't, it is a virtual voltage which must be kept separate from what your voltmeter measures across the motor terminals. You could infer it by measuring motor speed and using the motor constant you measured in another experiment. But it is a separate and unique voltage that must be identified separately from the supply voltage. You could use a subscript, perhaps B for back, but that could be confusing relative to B for battery. So now we are just quibbling over symbols. EMF has apparently confused you because forces and voltages are not the same thing, but you have not complained about the fact that a stack of electro-chemical cells has nothing to do with an array of cannons.
While there probably is a historical reason involving line integrals for the original use of EMF as the symbol for this term, the key is that a specific symbol is needed (just as there is a need for a specific symbol for the voltage at each node of a Kirchhoff loop) and that there will always be arguments about which mnemonic is best. Unless you concede to sentence length subscripts, which might not need to be standardized to improve communication.
Smokey:
--- Quote from: fourfathom on April 06, 2024, 01:35:19 am ---
--- Quote from: CatalinaWOW on April 06, 2024, 12:07:34 am ---In some sense these last couple of pages have been a variant of "Why can't we all just use the same words for everything." It would be so much easier if everybody just spoke English [...]
--- End quote ---
Everyone should speak West-Coast American English, as God intended.
--- End quote ---
Dude!
paulca:
--- Quote from: tszaboo on March 29, 2024, 01:27:11 pm ---
--- Quote from: Halcyon on March 28, 2024, 11:44:16 pm ---Regular expressions.
--- End quote ---
I won't even attempt that. My time is better spent on literally anything else.
--- End quote ---
It's better that way. Based on the number of regular expression bugs I find and fix I figure more people need to take the approach of "I don't understand this" and ask for help.
Probably the no.1 most common bug is over-greed and un-anchored wild cards.
.*eevblog.com
to match sub-domains, as an example.
A better example, but still very, very wrong, would then be:
.*.eevblog.com
Nope!
.*\.eevblog.com
Nope!
.*\.eevblog\.com$
Now we are getting somewhere.
trojan.eevblog.com.h8xzor.xx.tt
;)
What definitely goes into my pile of "I don't understand this", is anything beyond about middle school mathematics. Once the material comes from Mathematicians and not "normal people" I just stop following. For some reason, maths or particularly the language of maths ended up in the bin. I'm usually okay when the concepts are explained, but when I then get presented with a formula in a datasheet which contains greek, I'm immediately "Nope". Not worth my time.
On a more micro level, I have issues processing "inclusions" and "exclusions" on ranges. It's not that I have a problem, it's more that I can't give straight answers to those questions like "How many days between Monday and Wednesday?", without having to stop and think carefully if it's x-y, or if it's x-(y-1) or if it's x-(y+1) or x+1-y. If Monday and Wednesday are included then it's 3. If they are not it's 1. The "commonly interrupted answer" I believe is actually y-(x+1) which is 2 days. I still have to stop and think everytime.
I have programmer "out by one" paranoia.
Ground_Loop:
My brain lock: transitioning from time domain to frequency domain and back. I'm ok with the mechanics (math) of it, but just can visualize what the math is doing.
Zero999:
--- Quote from: Ground_Loop on April 08, 2024, 09:48:37 pm ---My brain lock: transitioning from time domain to frequency domain and back. I'm ok with the mechanics (math) of it, but just can visualize what the math is doing.
--- End quote ---
That's odd because I have the opposite problem. I can visualise transitioning from the frequency to the time domain, but I struggle with the calculations, partly due to my difficulty with the notation, as I've mentioned above.
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