DC Wave Questions

Sure... now, can you define "zero"?

E =IR

Since our resistance is fixed, it's the exact same issue, though perhaps easier to understand, with voltage. (I gave some consideration as to whether to post that with voltage or current references, and since "AC" and "DC" use the term "current", decided to go with current to avoid the easier path to the same statement you are making.)

Yes, the load impedance is a function R, L, C and frequency. L and C do matter anytime the voltage varies even on non-periodic wave and even if the voltage is always positive. On a pure DC voltage (constant, non-varying), L will represent a short-circuit while C will represent an open-circuit.

If the R+L+C are all in series, the +5V to +15V sine wave will, during the transient phase, first charge the capacitor to +10V, then (during the steady-state phase) the current will start to behave as a normal sine wave (reversing directions) even if the driving voltage never goes negative.

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.

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.

issues.

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

FWIW, most waveforms can be created as the sum of sine waves. I wrote an interesting computer demo once that showed how a sine and it's harmonics could be added graphically to form a better and better approximation of a square wave, running through what looked like Butterworth etc. responses.

Who do you want operating on your gall bladder? Someone who knows what he is doing or someone who is making it up as he goes along?

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

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.

Thanks, Floyd, for that excellent and understandable post.

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.

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.

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

--- 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 Professional Circuit Designer

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.

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

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.

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.

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?

2. >

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.

--- 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.

-- John Fields Professional Circuit Designer

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.