Maker Pro
Maker Pro

DC Wave Questions

P

Pooh Bear

Jan 1, 1970
0
2 questions about a fully DC Sine Wave....let's suppose you have a DC
Sine wave which varies from +5V to +15V peak-to-peak going into a load
with R, L, and C components.....

Question #1:
Is the load's impedance a function of R, L, and C (and wave frequency)
or is it simply just R (i.e. Z=R)? In other words does non-resistive
impedance (L + C) really only matter with an AC signal OR anytime
voltage varies periodically (even if it is all DC)?

What you describe is a 10V pk-pk sinewave sitting 'on top' of 10V DC.

The load current will depend on the RLC configuration. E.g. if there is series C then there
will be no DC load current. Only the AC component will be affected by reactance either way.
Question #2:
Would a "regular" negative peak detector ciruit, like shown here:

http://www.elektroda.net/cir/index/Detector Circuits/NEGATIVE PEAK DETECTOR.htmgative

work for the DC Wave described? Will it output +5V or do negative peak
detectors only work for AC signals?

404 error.

Graham
 
Actually, you haven't provided anything useful along the lines of
"tips" and you avoided responding to a previous reply of mine....but
anyway, what you say is interesting:
You are wrong in assuming the current flows in only one direction

O.K., then please let me know how current would not flow in only one
direction in the following example:
 
Again, is the term "DC Sine Wave" problematic because it is
Yes. DC by definition is zero frequency

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

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

Mac

Jan 1, 1970
0
Um, no. DC is Direct Current, i.e., current that flows in one
direction. For example, the output from a rectifier is DC but it
certainly isn't "zero frequency."

No, it is NOT DC. Sometimes when speaking casually people call it DC, but
more often it will be called rectified AC.

I agree with you that DC stands for Direct Current. But what is the
logical meaning of that? Who knows. The bottom line is that when a
waveform varies with time, it is NOT DC in popular useage.

I'm setting followups to sci.electronics.design.

--Mac
 
J

John Popelish

Jan 1, 1970
0
I will absolutely buy what you said, but understand the import of what
you're saying....you're saying that the language of "AC" and "DC" has
essentially been somewhat bastardized from its original meanings to
also mean zero-frequency and non-zero-frequency signals.

Now you are cooking with gas. Old words take on new meanings as our
needs change. Those words were coined when our understanding and use
of electricity was pretty primitive.
Therefore, to
describe a 10Vpp signal with a 10VDC offset as an "AC" signal is
actually contrary to the original connation of "alternating current"
since it (net) results in a signal which yields only a mono-directional
(i.e. direct) current flow (albeit time variant).

What you say about current applies only to a resistor connected across
that voltage. Connect a capacitor across it and the DC part is
ignored and AC (alternating current) passes through the capacitor as
if the wave were perfectly centered on zero volts.
So in a sense, you
could say I am holding "pure" to the original (circa 1890's) definition
of AC/DC while its use has been "officially" corrupted

I prefer "expanded", "enhanced", "extended" or "refined".
to cover the
concepts of "zero frequency" and "non-zero-freuency".

Agree?

Sure. The important thing is that the speaker and listener are using
similar definitions of the words in use, or there is bound to be a
misunderstanding.
 
M

Mac

Jan 1, 1970
0
If the low peak of the sine wave (and the rest of the the sine wave for
that matter) is "fully" above the "zero" reference point, then isn't it
true that the current DOES NOT alternate? That is to say, that current
only flows in one direction....i.e. "direct current"? Isn't it also
true that if the low peak of the sine wave is -0.00001V then the sine
wave results in current flowing in both direction (albeit for a
nanosecond)....i.e. "alternating current".....I'm not arguing that my
use of nomenclature is "pure" or conventional....but I don't see how it
is fundamentally wrong, without merit, or lacking a reasonable
basis.....

To an electrical engineer, at least, DC means time invariant. I suppose DC
and AC have become misnomers. For example, a sinusoidal Voltage waveform
across an open circuit would be called AC even though no current flows.

And the voltage across a battery's terminals would be called DC even if
there is no load, and hence no current.

If you talk to EE's, you will have to get used to them using the terms
this way.

I am not sure where to set followups to, so I guess I'll just post to all
four groups, and leave followups unset.

--Mac
 
M

Mac

Jan 1, 1970
0
I concede my terminology is anti-convention, and "wrong" (with respect
to convention) BUT I disagree with you here:


If you were given a sheet of paper a week ago, with only the phrase "a
fully DC sine wave" on it, and you were asked to come up with as many
realistic possible meanings, I have to believe that you could have only
come up with one (and rather quickly)

If true, then your statement:


would hold true about "a fully DC sine wave" with respect to
convention/"old definition" but not with respect to "communication" or
ambiguity....while not "pure" or conventionally correct, is there
really any other possible interpretation of "a fully DC sine wave" and
therefore wouldn't you agree that being a "hyper-stickler" on this
point is really not justifiable?

Again, isn't there more ambiguity (poorer communication) in your
description:


versus:

a "fully DC sine wave" versus "a partially DC-offset AC sine wave"

Ban and others are trying to educate you. You are resisting fiercely.

As I said elsewhere, DC and AC have become (or perhaps always
were) misnomers. In electrical engineering circles, the terms can be
applied to ANY signal, even if there is no current at all.

DC can be thought of as the average value of a waveform, or the zero
frequency component, or the offset, in case of a sinewave.

Your term "DC sine wave" makes you sound ignorant of engineering
terminology. If that is not a good enough reason for you to drop it, then
maybe you should avoid future posts to sci.electronics.design, where many
or most of the posters are electrical engineers.

--Mac
 
W

w_tom

Jan 1, 1970
0
The term DC sine wave is much like Magellan still claiming
the world is flat after he circumnavigated the earth.

Your wave could be a sine wave with a DC offset voltage. Or
what you are calling DC might be either a step function or an
impulse. DC would make the capacitors and inductors
irrelevant in your original question. Your question is about
L, R, and C. Therefore DC is not part of the discussion.

Now, what kind of waves (sine, exponential, step, impulse,
etc) - waves singlely or combined - do you want to ask your
LRC questions about? There is no possible answer if asking
about a DC sine wave. Move on to ask about waves that really
do exist.
 
Go back to the original few posts to see how it got started....despite
being explicit about the specs of the wave, someone childishly objected
to my casual usage of "DC sine wave".....would it have been
objectionable had I used "a fully DC-offset sine wave"?......again,
I've never claimed that I was using "official" or
conventionally-correct teminology or nomenclature....I just really
object that anyone would object to what I was saying, when its meaning
was explicitly stated (using actual numbers) and the phrase "fully DC
sine wave", although conventionly queer, is not at all cryptic or hard
to figure out......if I were a chemist and someone said "200 degrees
above the freezing point of water", I wouldn't mock them, just
respectfully point out that it's more common to say "20 degrees above
the boiling point of water".....I would consider the person ignorant of
the conventional terminology, but I would consider the person dead-on
if he were talking about 232 degrees F.
 
Go back to the original few posts to see how it got started....despite
being explicit about the specs of the wave, someone childishly objected
to my casual usage of "DC sine wave".....would it have been
objectionable had I used "a fully DC-offset sine wave"?......again,
I've never claimed that I was using "official" or
conventionally-correct teminology or nomenclature....I just really
object that anyone would object to what I was saying, when its meaning
was explicitly stated (using actual numbers) and the phrase "fully DC
sine wave", although conventionly queer, is not at all cryptic or hard
to figure out......if I were a chemist and someone said "200 degrees
above the freezing point of water", I wouldn't mock them, just
respectfully point out that it's more common to say "20 degrees above
the boiling point of water".....I would consider the person ignorant of
the conventional terminology, but I would consider the person dead-on
if he were talking about 232 degrees F.
 
B

Ban

Jan 1, 1970
0
Go back to the original few posts to see how it got started....despite
being explicit about the specs of the wave, someone childishly
objected to my casual usage of "DC sine wave".....would it have been
objectionable had I used "a fully DC-offset sine wave"?......again,
I've never claimed that I was using "official" or
conventionally-correct teminology or nomenclature....I just really
object that anyone would object to what I was saying, when its meaning
was explicitly stated (using actual numbers) and the phrase "fully DC
sine wave", although conventionly queer, is not at all cryptic or hard
to figure out.....

It is like somebody says to you you are an intelligent idiot. Of course you
know what he means, don't you. But there is a contradiction in those words.
You expose yourself being a layman, being not educated, having slept at
physics. At the best you might have other talents, but apparently not in
engineering. Do you want to appear like that, well than just erase that
"intelligent" in front of ...
Intelligence is not making no mistake, but avoiding to make the same mistake
twice.
 
Thank you for your comment, but I respectfully disagree....I could
really care less if someone used the correct terminology in describing
something, as long as I could understand what they were talking
about....in fact, I run into this situation alot - I never, ever,
correct the use of improper terminology (until the person is
finished)....I find it to be stifling of the other person and the point
they are trying to make.....thousands of times per day, people (in
industry) with only high school diplomas (or less) in industry make
absolutely brilliant observations and suggestions, but well over 80% of
these are ignored, poo-pooed or brushed-aside, by people with advanced
college degrees....many times, in part, due to the unsophisticated way
in which the ideas are expressed.....it definitely is frustrating
trying to understand what someone is saying when they use unfamilar or
unconventional terminology, but it really can pay off big to suffer
through it......
 
D

Don Bowey

Jan 1, 1970
0
Let me try this:

would you object to

"a sine wave which (net) results in a current that only flows in one
direction"

Yes, I object.

Don
 
B

Bob Monsen

Jan 1, 1970
0
Thank you for your comment, but I respectfully disagree....I could
really care less if someone used the correct terminology in describing
something, as long as I could understand what they were talking
about....in fact, I run into this situation alot - I never, ever,
correct the use of improper terminology (until the person is
finished)....I find it to be stifling of the other person and the point
they are trying to make.....thousands of times per day, people (in
industry) with only high school diplomas (or less) in industry make
absolutely brilliant observations and suggestions, but well over 80% of
these are ignored, poo-pooed or brushed-aside, by people with advanced
college degrees....many times, in part, due to the unsophisticated way
in which the ideas are expressed.....it definitely is frustrating
trying to understand what someone is saying when they use unfamilar or
unconventional terminology, but it really can pay off big to suffer
through it......

"There's glory for you!"
"I don't know what you mean by 'glory,' " Alice said.
Humpty Dumpty smiled contemptuously. "Of course you don't—till I
tell you. I meant 'there's a nice knock-down argument for you!' "
"But 'glory' doesn't mean 'a nice knock-down argument,' " Alice
objected.
"When I use a word," Humpty Dumpty said, in rather a scornful tone,
"it means just what I choose it to mean—neither more nor less."
"The question is, " said Alice, "whether you can make words mean so
many different things."
"The question is," said Humpty Dumpty. "which is to be master—that's
all."
 
L

Leonard Caillouet

Jan 1, 1970
0
I assume that you are meaning that you have 10vpp wave with 10vdc offset.
The answer is the latter, but the terminology that you are using is
incorrect. It is not all dc. It IS a varying current with a dc component.
The impedance must account for all factors.

Leonard
 
L

Leonard Caillouet

Jan 1, 1970
0
cross posting corrected

It is not childish to correct something that does not follow convention and
does not make sense. You have been given the answer to your question
several times and continue to argue your terminology makes sense.
Apparently you do not understand that dc has a specific meaning and a sine
wave is not dc. You described a signal that had both as components. The
effect on the dc component is the resistive part, the effect on the sine
wave is the impedance part. Calculating the impedance has to account for
the non-resistive effects.

Leonard
 
R

Richard Henry

Jan 1, 1970
0
I concede my terminology is anti-convention, and "wrong" (with respect
to convention) BUT I disagree with you here:
misunderstand you

If you were given a sheet of paper a week ago, with only the phrase "a
fully DC sine wave" on it, and you were asked to come up with as many
realistic possible meanings, I have to believe that you could have only
come up with one (and rather quickly)

On the other hand, given a sheet of paper with a drawing of your waveform on
it, I don't think too many readers would have described it as "a fully DC
sine wave".
 
R

Richard Henry

Jan 1, 1970
0
Thank you for your comment, but I respectfully disagree

Another irritating newbie habit you have is replying without keeping at
least a pip of the message to which you are replying.
 
Top