DC Wave Questions



Boy, you are *pedantic*!
Can't we just define DC as current that doesn't vary "much" for at last a "long" time. Granted that is ambiguous, but what else would we the argue about, weather?
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Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
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Floyd L. Davidson wrote:

No.
Sum a 1 volt peak sinewave with a 0.6 volt dc term and you have a waveform whose polarity continuously changes but whose average value is continuous.
Looking at the Fourier terms makes this waveform perfectly clear. Calling it "AC" or "DC" does not.
"AC" or "DC" are gross and meaningless oversimplifications.
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Don Lancaster
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Hey, you moved *my* goal post! I said nothing about average values. If it wiggles, it's AC. The difference is that you are being so precise that you're saying if it wiggled since the dawn of time, it's AC. I'm just saying that if it was so long ago that I can't remember (which seems to be a pretty short time anymore), that's long enough. :-)

EXACTLY! And while you and I can make jokes about just how pedantic we should be with definition of terms, the fact is that anyone who actually thinks "AC" and "DC" are the determinative definitions based on word meanings, is going to be wrong.
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wrote:

--
No, you have a waveform with a polarity which changes _periodically_,
making it an AC signal. Do the electrons traversing the circuit
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John Fields wrote:

It's not unusual to speak of the AC and DC _components_ of a waveform that does not readily satisfy the simplification.
One also speaks of _DC offset_ of an otherwise AC signal.
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And, according to what you've said in other posts, if that were a 0.6 volt peak sinewave with 1.0 volt dc, it wouldn't be.
But your definition of AC is faulty, because in fact they are the same thing, and *both* of them contain an AC component and a DC component, even if the general direction of electrons is always the same.

Except, polarity reversals are not significant to the definition of AC.

He's right.
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Item 3 is correct. That is because "varying DC" *is* AC.
It is AC even if the axis is shifted far enough to avoid polarity reversals relative only to some specifically defined 0 current.
The reversals are relative... to the steady state condition, not to some magical 0 current where supposedly no electrons are flowing.
Otherwise, instead of two types, you are dividing circuit analysis into three types, two of which are identical in all significant respects other than an arbitrary definition that is meaningless.
It makes no sense to say that "Impedance laws apply equally" and then claim that the two are not identical.
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GIVE IT A REST !
Oh ! & Stay The Fuck Away from my Gal, Bladder.
oy
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Strictly speaking, I believe the reactance (part of impedance) equations apply to any variation in current magnitude. Their appropriate application does not in any way require reversing the charge.
1) I think one needs to define the term "alternating current" by its phenomena rather than define it by what applies to "AC". In other words, define AC as alternating current -rather than defining AC as "anything requiring an impedance calculation because of its magnitude variation". ( OK, all scientific definitions require definitions in terms of other defined concepts; thus voltage and charge are defined in terms of force. And yes, any phenomena in its purest defined form uses the fewest of the core units, and only the core units, of the measuring system. And yes, since, unlike in the British ft-sec-lb system, force is not a core unit of the metric kg-sec-m system, one cannot be as "pure" in the metric system with many definitions as one can be in the British system, "decile" convenience notwithstanding)
2) There are two phenomena and two descriptive words if one uses the mathematical description of the changes associated with current: changes in current _direction_ and changes in current _magnitude_.
There are three (or more) phenomena if one uses only the two descriptive terms _AC_ and _DC_, well evidenced in this thread: changes in direction and magnitude, changes in magnitude only, or no changes in either magnitude or direction. Three phenomena defined using only two words for those three cannot be specific and exclusive enough for a rigorous definition. The middle condition, the overlap as it were, ends up wanting.
3) In the definition approach to a phenomena, one deals with the descriptive term and the phenomena itself and ignores the present attached effects. Once the definition is had, then the phenomena's interaction with other phenomena can be determined. Yes, having such rigor in a definition can be more complicated in its application.
In the application approach to defining a phenomena, one defines by addressing what equations, etc., apply to the condition. In this approach, you end up in circular arguments, chasing your tail. Something always will not fit. Like changes in magnitude without changes in direction.
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Exactly.
What value does that have? The problem is circuit analysis, which requires the division between DC and AC, and the only division that makes sense is between non-changing current and changing current.

The problem is defining something with no practical value. If AC is a changing current, that includes changing polarity, and covers the actual significant difference from DC. If AC is defined only as changing polarity, we also have to have an entire separate set of identical functions and definitions, one for "varying DC" and one for "AC". Since the analysis is the same, there is no point in separation of the two.
And "varying DC" is a contradiction in terms to begin with. Do we actually need *four* states:
1 -- DC 2 -- Varying DC 3 -- AC 4 -- Steady AC
Boy, that should may first year text books *really* interesting!
Either that or we are back to Don Lancaster's correct statement that they are meaningless terms anyway. They certainly are if that is the way they are defined!
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On Mon, 13 Jun 2005 07:58:46 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) wrote:
*Snip*

Don first said: --------------------------------------- '"DC" is simply the first (or "offset" term in the Fourier expression of any repetitive waveform.
"AC" are all of the remaining components.' ----------------------------------------
Then he said: ---------------------------------------- '"AC" or "DC" are gross and meaningless oversimplifications.' ----------------------------------------
Which are we to believe?
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There is no contradiction, so what is wrong with understanding both statements?
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Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
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On Mon, 13 Jun 2005 12:11:31 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) wrote:

The difficulty is understanding just what Don was getting at. His first post in its entirety was:
--------------------------------

Total and utter horseshit.
"DC" is simply the first (or "offset" term in the Fourier expression of any repetitive waveform.
"AC" are all of the remaining components.
Changing the relative amplitude of the terms does NOT in any manner change which is the first term and which are the remaining terms.
DC, of course, cannot exist at all ever. Because it would have to be unvarying through infinite time.
Tutorials on my website. ---------------------------------
In this post he seems to be suggesting that Bob Penoyer's definitions of AC and DC were "Total and utter horseshit", and follows with a couple of definitions which appear to be offered as alternative definitions which presumably Don thought were *not* "Total and utter horseshit". But then in his next post, he says:
--------------------------------- "AC" or "DC" are gross and meaningless oversimplifications. ---------------------------------
If he thinks "AC" and "DC" are gross and meaningless oversimplifications, why would he offer alternative definitions of AC and DC to those given by Penoyer which Don thinks are "Total and utter horseshit"? Why offer definitions of AC and DC at all if he thinks so poorly of the terms? Because when people see him first disparaging someone else's definitions and then offering definitions of his own, they're going to think he believes his own definitions are good ones.
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On 6/13/05 10:01 PM, in article snipped-for-privacy@4ax.com,

Horse pucky. I think I can afford to miss the tutorials on your website.
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Pure DC, or something close to it, is actually pretty rare stuff.
Even on battery power plants, which are extremely good filters, there is some AC on the leads of just about anything powered from the battery unless either the battery or the load is all but embedded in the other.
For example, the 48 volt battery plants that telephone companies have, use some rather large cables to supply voltage to equipment. Yet a filter is required at every fuse bay to decouple the AC noise on the supply cable from the equipment in the bay. Even then, the supply lines have an astounding amount of AC noise on them.
That was particularly true back in the days of mechanical switches, when a telco switch was filled with "DC" switched lines that had mechanical contacts, and most of the loads being switched were inductive.
There is even more of the same going on in modern digital switching systems, minus the inductive kick, but those are filtered much more effectively because unlike the old mechanical monster, these new ones will malfunction themselves if the noise isn't filtered out.
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Floyd L. Davidson wrote:

<snip>
And is pretty cold - ask Thevenin.
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Sue

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On 6/14/05 2:28 AM, in article snipped-for-privacy@barrow.com, "Floyd L.

I agree with your examples of DC power supplies and AC noise. Been there, done that.
Defining how may angels can dance on a DC power cable without having to redefine it is pointless, however. Everyone I knew in the telco industry had good, workable terms for the cause of the need for filters, not only at the FB, but at the equipment rack too; it was noise, trash, crap. spikes....., but the 48V and 130V "power" were always DC and we knew the noise had to be dealt with as AC riding the DC. No other esoteric, mindless definitions are needed even though the terms AC and DC may be misnomers. They are historic and work very well.
Don
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Don Bowey wrote: No other esoteric, mindless

The only tiny problem is that the definitions are wrong.
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Don Lancaster
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Please give us the correct definitions. In an earlier post you said:
'"DC" is simply the first (or "offset" term in the Fourier expression of any repetitive waveform.
"AC" are all of the remaining components.'
But then in your next post you said:
'"AC" or "DC" are gross and meaningless oversimplifications.'
Does this comment apply to your own earlier definitions? Are you saying that even you can't give definitions to AC and DC that aren't "gross and meaningless oversimplifications"?
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