DC Wave Questions

Now, you're trolling.

Fuck off and read a f****ng book.

Then, ask in sci.electronics.basics, _after_ you "get" some BASICS.

Sheesh! Rich

you

If that happened to me, I would snitch out the teacher to the principal, or snitch out the professor to the dean, because the teacher/prof is obviously incompetent, and has no business teaching wholesale bullshit to impressionable students.

'nuff said?

Go read a _real_ book.

Sheesh! Rich

AC/DC is a false dichotomy. Some signals can have both components. Rectified AC is not just DC and it is not just AC, either. It has both DC and AC components.

As I said above in this post, the rectified signal has AC and DC components. When you filter out the AC using a capacitor, the DC begins to dominate. When the AC is small enough, you may decide to call it DC. Practically this presents no problem. Very small AC signals are often ignored.

This does not match with very long established useage AT ALL. For decades, the terms AC and DC have been applied to voltage signals where there may not even be a current. AC and DC are misnomers. The simple definition you put forth above is just wrong, at least as far as engineering parlance is concerned.

--Mac

I can't vouch for the historical facts, but as far as zero frequency and non-zero-frequency goes, you are pretty much correct.

Another point to note is that many signals have both AC and DC. It is not a dichotomy. The signal you mentioned at the start of this thread has both AC and DC.

Historically, I think what happened is that the terms originally were used to describe two competing power sources (the war between those who wanted a DC power grid and those who wanted an AC power grid was surprisingly fierce). Later, the terms started getting used to describe signals, and that is probably when the shift to the ZF- and NZF-meaning happened.

Also, there may be people out there who still think of AC and DC in the original sense (I'm not sure about this, but maybe people who work with power stuff exclusively), but among electrical engineers, the signal perspective prevails.

--Mac

Well, look at it this way: almost all of us had to read your post twice and think about it to make sure we understood the most likely meaning of it.

If you worded it differently, the meaning would be crystal clear, and we would only have to read it once. So in a sense, it is inconsiderate and a waste of our time to post it in such a way that we can't immediately understand. You can easily be forgiven for doing this once out of ignorance.

Anyway, I agree that some people were rude to you. But you haven't exactly showed yourself to be receptive to advice, either.

--Mac

Pretty much. Even in other languages I believe that terminology is basic - certainly German is the same (Gleichstrom. Wechselstrom.)

Try a simple experiment. Build a simple oscillator powered off of two 9V batteries ie +/- 9V.

Now measure the output. with the scopes gnd probe on the point between the two batteries, and again with the gnd probe at either exterme of the batteries.

In the first case you will measure a signal that oscilates around 0, in the other two cases it will be entirely above or below 0. The wave has not changed. It would make absolutely no sense to describe it in one case as AC and in the others as DC. As much to the point describing as DC would make understanding it more difficult.

Just as there is no absolute inertial reference frame, there is no absolute voltage reference.

Robert

Yes, I would object. You can't predict that without knowing the whole circuit. Connect your DC sine wave to a reactance and current (and energy) will indeed flow in both directions.

It is fundamentally meaningless. A sine wave is a defined mathematical function:

y = a sin(x)

I think what you are talking about is a sine wave with an added DC component:

y = (a sin(x) + b)

which is not purely a sine wave, nor is it purely DC. It's "a sine wave plus DC" if you like.

Referring to "a DC sine wave" is analogous to referring to "a curved straight line".

No, not just convention, this is engineering. The language we speak is mathematics. I think I just showed you why.

I could only think of only one thing: "This guy is not an engineer, or scientist, or mathematician!"

--- That's because you want to excuse yourself for your faux pas by saying that if someone else committed it you would ignore it as long as you could understand what they were saying, so everyone should follow your example. What you don't seem to understand is that unless they were using the language properly, your take on what they meant to say might be wrong. Your use of "DC sinewave" instead of "sinusoidally varying DC" or "a sinusoidally varying unipolar voltage" is precisely that sort of an occurrence and your use of "DC sinewave" was critcised because there is no such thing as a DC sinewave. This is a technical forum and, rather than argue with the people who have taken time out of their lives to correct you, you should do as the Romans do and adopt the language we use instead of trying to force us to try to understand what you're trying to say on _your_ terms. Remember, it was you who was looking for answers, not us.

---

--- I'm sure you do.

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--- You may be relating to how you feel when you're corrected. I find that many people accept correction graciously, and the sooner the better in order to help them to keep from making fools of themselves over and over again.

---

--- I've never noticed that, and I doubt whether you have either or that you have anything to prove that 80% number. Sounds more to me like you have an axe to grind.

---

--- And just what gifts do you have to offer us for suffering through _your_ presentation?

-- John Fields Professional Circuit Designer

I couldnt open the link however quite a few negative peak detectors i have seen do assume the negative peak goes below 0v, and so wil probably not give the output you expect (wich would be +5v), but would be easy to make a circuit that does. it also depends what you tie the reference point to.

I think also the simple dictionary meaning of DC is being taken too literaly here, if it was taken fully it would aply only to currents and not voltages if there was an infinite impedance load wich would be meaningless. I gues it was mostly aplied to power distribution systems at the time it was first used to distinguish between the two oposing methods of AC and DC.

However sinewaves are not DC !(wich the term DC sinewave is trying to imply) as a sinewave is centered about zero volts.

what you have is an arbitrary waveform consisting of dc and a sinewave. this does not make the sinewave a dc sinewave, but just a sinewave with dc added. if you want help here i gues youl just have to go along with this, there seems little benefit to you to argue about it wich seems to be going on at length.

Colin =^.^=

("DC sine wave")....

Just because someone else used the term doesn't make it right ! There's plenty of rubbish spouted on the net.

Graham

If you learn the math the definition of AC and DC is totally irrelevant. Your original Question #1 indicates that you don't know the math. That is fine; it is something you can learn, but no amount of quibbling over semantics is going to change the principles of circuits.

Forget the encyclopedia, learn differential equations instead. Encyclopedia are for junior high school kids.

Indeed - depending on the configuration of the R, L, C combination there may no DC component *at all* and the current would be purely a.c.

Graham

terminology ("DC sine wave")....

plenty of rubbish spouted on the net.

Once in a while someone coins a new term like Heinleins' waldo... but I don't think its going to happen here.

What has been described is similar to the waveform one would see on the grid of a class A tube circuit. (but negative voltage of course)

There are a number of waveforms that go in only one direction relative to ground such as sawtooth waves, square waves, and triangle waves. To refer to these as say a "DC triangle wave" would be equally confusing without further qualification.

The closest descriptor that I can think of offhand that might meet with general acceptance would be "bias signal".

I object to all of the above. Go read Scroggie's "Second thoughts on Radio Theory".

------------- Don't freak out, a sine wave with a DC offset so that it is all pulsating DC is not at all unusual, every transistor amp has one since transistors can only accomodate one polarity of current.

-Steve

------------------ It's not "rectified AC", as that would be fullwave rectified, and not a sine at all. Any current graph can contain a DC and an AC component, and the calculus shows this. Any capacitor will pass the AC component and not the DC, as in a simple transistor amp. Why are you having trouble with this, a sine is a shape, not a polarity!!

-Steve

In this case, the OP actually used the words "sine wave", which would appear to preclude any such flexibility, anyway.

Where it matters, I prefer the use of "steady" or "varying"

"AC" and "DC" have overtones of Edison, Tesla, Ol' George Westinghouse, and the unfortunate Mr. Kemmler.