DC Wave Questions

[Kitchen Man]

But rather than look at DC as current going all going in one
direction, and AC as anything else, it is *far* easier to view
it as AC is any current that is changing, and DC is anything
else (i.e., the current is steady).

Technically those definitions are exactly the same, but one
leads to a lot of confusion.

Thanks, Floyd, for that excellent and understandable post.

 

[Kitchen Man]

Nice parse-job.....here's my original entire comment in context:


You conveinently left out the "OR...." part.

If we may plunge for a moment into basic boolean logic, the "OR" part
is no longer necessary once one part of the proposition is shown to be
true. Thus, not only was his omission convenient, it was proper.

You actually proved my
point that DC is DEFINED (i.e. by convention) as "zero frequency".
Is it that weird to posit that the superior concept with respect to
considering any signal as AC or DC, be the actual NET current flow? I
could see your point if signals were classified as either "ZF" ("zero
frequency") or "NZF" (non-zero frequency") but we are dealing with "DC"
or "AC"

If nothing else, your stubborn adherence to a flawed terminology and
lack of openness to furthering your understanding will make you look
like an idiot in a job interview, should you ever decide to pursue
career advancement in the electronics industry. Please note that I am
not saying you are an idiot, just that you will look like one in an
interview. The interviewers will assume you know very little about
the basics of the craft if you carry on like this, or at the very
least will see you as a detriment to teamwork. HTH.

 

[daestrom]

[email protected] wrote:

The circuit is pretty much unconventional (but sure smart!). No, it
will not output +5V. The circuit is meant to detect only negative
voltages and can only output zero or negative voltage. But I suggest
that your try building it and see what happens. You might just get
lucky.


You're welcome. I hope you now understand that your +5V to +15V voltage
is better called "varying DC". I've never seen an EE book that will say
"DC Sine Wave" for the voltage you described, and rightly so because a
sine wave implies reversing directions.

Or, one might refer to this as 10VDC with an AC waveform superimposed. The
AC waveform varies sinusoidally with 10 V peak-peak. One can then solve two
circuits, the DC one with just R and 10VDC, and the AC one with R-L-C.
Combining the currents from the two solutions should be equivalent to the
original circuit.

I agree, that 'DC sine wave' is a misnomer. It makes it sounds like the
speaker doesn't know AC from DC. In order to not sound foolish, it would be
better to use one of the alternatives suggested.

daestrom

 

[John Fields]

It is equally a shame that there are those that are sometimes
incapable of offering correction gracefully, eh, John? If it pains
you so much to engage in your ungracious edifying, perhaps you would
do well to bugger off, and leave the stress of educating imbeciles to
those with more patience.

---
Well, Al, correction (no matter how gently offered) is often met with
varying degrees of resistance, particularly by those who have become
convinced that their way should be temporarily accepted as the 'right'
way, for their convenience, regardless of whether their way conforms
to universally accepted standards.

Case in point, the OP, whose attitude seems to be (and I paraphrase)
"You know what I mean, so why should I have to say it your way?"

As for me, I'm perfectly capable of conducting myself politely in the
presence of polite company. I'm also perfectly capable of atrocious
behavior and have no qualms about stooping to that level if, in my
opinion, the situation warrants it.

Finally, I don't see how you came to the conclusion that it pains me
to engage in the edification of imbeciles. Actually, it's quite
gratifying to be able to take on the challenge of breaking through the
barrier of ignorance and realize that you've shown someone how to use
a tool they didn't even know they owned.

 

[John Fields]

On 10 Jun 2005 23:06:10 -0700, [email protected] wrote:

If nothing else, your stubborn adherence to a flawed terminology and
lack of openness to furthering your understanding will make you look
like an idiot in a job interview, should you ever decide to pursue
career advancement in the electronics industry. Please note that I am
not saying you are an idiot, just that you will look like one in an
interview. The interviewers will assume you know very little about
the basics of the craft if you carry on like this, or at the very
least will see you as a detriment to teamwork. HTH.

 

[Floyd L. Davidson]

Put an ammeter there and it says zero. That's zero. Electrons bouncing
around in the conductor have an average net displacement, over time, of 0.

Is this an AC ammeter, or a DC ammeter? (And isn't that just a voltmeter
anyway, in most actual cases????) Hmmm...

You can't escape the fact that voltage and current are joined at
the hip, they are for all practical purposes different expressions
of the same thing. Whatever affects one *has* to have affected the
other.

Current is a different issue from voltage because voltage is a relative
quantity.

No more or less than current. They are joined at a hip called
Ohm's Law.

It is a type of measurement of a change in field between two
locations. Current is a rate of flow of charge at a single location (well,
typically, through a single Gaussian surface), and is measurable at that
location, and does not have the ambiguity that voltage has. It does not
need a reference. If I say that my toaster is running at 120V and 8A, you
may ask "120V relative to what" and I'll answer "neutral". You would not
ask "8A relative to what".

8 Amps from where? To where? Through were?

Relative to where?

Since we can discuss current using only voltage as the variable
(resistance being a constant in this example), *anything* you
can say about voltage is directly related to current.

One of the overall things that you *have* to keep in mind is
that periodic reality checks are necessary. One of them is the
fact, repeated by many in this thread, that "DC sine wave" is a
contradiction of terms. If your definition makes it possible,
your definition *can't* be right.

My point still stands, that if the current is changing, it is by
definition AC, and current not changing is DC. Trying to look
at it as DC is all in one direction and anything else is AC,
doesn't work.

 

[Don Lancaster]

A rectified AC waveform contains DC and AC components but if the
current isn't changing direction, it isn't alternating current. And,
if it isn't AC, it's DC.

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.



--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Floyd L. Davidson]

DC, of course, cannot exist at all ever. Because it would have
to be unvarying through infinite time.

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?

 

[operator jay]

0.

"Put and ammeter there" and if it says +300mA to +800mA back and
forth, then it's Alternating Current, innit?

It is not changing polarity. I would hesitate to call it alternating
current. On the "dc sine wave" issue, I wouldn't even get into that debate.
To me the terms involved are open to too many interpretations. As evidenced
in this thread, I suppose.

j

 

[Floyd L. Davidson]

It is equally a shame that there are those that are sometimes
incapable of offering correction gracefully, eh, John? If it pains
you so much to engage in your ungracious edifying, perhaps you would
do well to bugger off, and leave the stress of educating imbeciles to
those with more patience.

Is patience required though?

I'm always reminded of a young lady I met once, many years ago
employed by Northern Telecom Inc to provide training on a
mainframe computer program to USAF personnel. This lady showed
up and started teaching the GI's, one at time. She first
latched onto a 16 year Staff Sargent (that suggests he might not
have been too bright). He'd been working with
telecommunications for all 16 of those years and didn't know
that a Class C Autovon line was the kind he could call home on
for free (every Airman figured that out in 6 days).

So, we thought the lady probably ought to be warned. And not
being a GI myself, it was sort of agreed that I'd tell her. We
had not counted on this lady being, ahem... perceptive. Not to
mention independent, ornery, and several other adjectives.

I hinted to her that the Sarge was the worst case example, and
maybe she shouldn't waste too much time on him. She growled at
me, and said something about my head and a dark place, and said
she had "A degree in teaching fucking idiots."

Apparently patience is not part of the requirement?

Somewhat ruffled at a gal 10 years younger than me getting the
best of me in that way, I decided to get back! There was this
almost friendly young Security Policeman who came by now and
then to check our credentials to be in a secure area. Of course
every SP lives for the day he can "jack up" somebody. So I
suggested we had a really good candidate to play games with! He
figured that was just a great idea, and followed me as I led him
to where he could perform this duty for his country.

But, alas, he came around the corner and this asshole young
lady looked at this asshole young Security Policeman, and he
looked at her... and I saw the look in their eyes and knew all
was lost. It was like in a movie! They locked on, you could
hear the bells ring! You could see them shiver! It was a
*classic* love at first sight! Danged guy spent the next *two*
*hours* talking to her, and they dated the entire time she was
there.

Patience... did teach me something!

 

[John Fields]

My point still stands, that if the current is changing, it is by
definition AC, and current not changing is DC. Trying to look
at it as DC is all in one direction and anything else is AC,
doesn't work.

---
Your point is flawed. Alternating Current, by definition, causes
electrons to move in one direction for a time, and then to reverse
direction for a time.

The sinusoidally varying unipolar voltage under consideration _always_
forces electrons to move in one direction only.

Since the voltage varies, the current will also, but the _direction_
in which the electrons are travelling will never change.

That means that the signal is DC. A varying DC, but DC nonetheless.

 

[Don Lancaster]

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?

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.

--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Floyd L. Davidson]

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.

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.

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.

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.

 

[Floyd L. Davidson]

That isn't true.

The sinusoidally varying unipolar voltage under consideration _always_
forces electrons to move in one direction only.

A non-sequitor.

Since the voltage varies, the current will also, but the _direction_
in which the electrons are travelling will never change.

If it varies, it's AC.

That means that the signal is DC. A varying DC, but DC nonetheless.

If there is such a think as "varying DC", connect a load to
it... through a capacitor. Now, how do you describe the effect
that load has on your "varying DC". The load see's *only* AC,
even according to your definition. That AC came from somewhere,
and it certainly was not generated by the capacitor.

That's because AC is *not* defined by any change in direction,
but only by a rate of movement change.

 

[John Fields]

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.

---
No, you have a waveform with a polarity which changes _periodically_,
making it an AC signal. Do the electrons traversing the circuit
change direction? Yes. Do the electrons in a DC circuit ever change
direction? No.

Ergo, because of the periodic polarity reversals what you're looking
at is AC.
---

Looking at the Fourier terms makes this waveform perfectly clear.
Calling it "AC" or "DC" does not.

---
Why go there? Your description was adequate to indicate that polarity
reversals occur, therefore making the signal voltage alternate between
two different polarities, therefore making the current alternate
between polarities as well. That's why it's called "Alternating
Current".
---

 

[CJT]

---
No, you have a waveform with a polarity which changes _periodically_,
making it an AC signal. Do the electrons traversing the circuit
change direction? Yes. Do the electrons in a DC circuit ever change
direction? No.

Ergo, because of the periodic polarity reversals what you're looking
at is AC.
---


---
Why go there? Your description was adequate to indicate that polarity
reversals occur, therefore making the signal voltage alternate between
two different polarities, therefore making the current alternate
between polarities as well. That's why it's called "Alternating
Current".

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.

 

[Floyd L. Davidson]

---
No, you have a waveform with a polarity which changes _periodically_,
making it an AC signal. Do the electrons traversing the circuit
change direction? Yes. Do the electrons in a DC circuit ever change
direction? No.

Ergo, because of the periodic polarity reversals what you're looking
at is AC.

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.

---


---
Why go there? Your description was adequate to indicate that polarity
reversals occur, therefore making the signal voltage alternate between
two different polarities, therefore making the current alternate
between polarities as well. That's why it's called "Alternating
Current".

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

He's right.

 

[The Phantom]

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.

Didn't you just say in your immediately previous post:
----------------------------------------------------------------
""DC" is simply the first (or "offset" term in the Fourier expression
of
any repetitive waveform.

"AC" are all of the remaining components."

 

[Floyd L. Davidson]

It is not changing polarity. I would hesitate to call it alternating
current. On the "dc sine wave" issue, I wouldn't even get into that debate.
To me the terms involved are open to too many interpretations. As evidenced
in this thread, I suppose.

Where *do* you get this requirement for changing polarity? We
don't call it "Alternating Polarity", we call it "Alternating
Current". If the current is being altered, it's AC. You keep
talking about AP, and it isn't the same.

 

[Bob Penoyer]

Total and utter horseshit.

Look, if the current's not alternating its direction, it's not
alternating current. To be clear, just because its amplitude is
changing does not mean it is alternating. In particular, a rectified
AC waveform it isn't changing direction.

There are certainly AC components in the waveform. But the sum of all
the components, including the DC component, never changes direction,
so the total signal is a DC signal. Here, "DC" does NOT mean
"constant"; it means unidirectional.