DC Wave Questions

Yes, your term "DC sine wave" is objectionable because it is fundamentally wrong.

I'm sure that one of your assumptions is that AC voltages flow through a capacitor. They do not. Now you go hit the books and discover how a varying voltage gets from one side of a capacitor to the other. Then you will be close to seeing your error.

Don

Here's one last tip to help you with the homework assignment I gave you earlier: You are wrong in assuming the current flows in only one direction.

Don

Let me try this:

would you object to

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

if you buy that, would you then accept it to be partially condensed into:

"a sine wave which (net) results in a non-polarity-alternating current"

if you buy that, would you then accept this:

"a sine wave which (net) results in a direct current"

and then

"a (net) direct current sine wave"

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. 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). 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 to cover the concepts of "zero frequency" and "non-zero-freuency".

Agree?

Maybe you shouldn't believe everything you read. DC has:

1. Constant amplitude (that's not to say you can't change it.
2. Frequency of 0 Hz. Also, a non 0 frequency does not imply polarity changes.

Tam

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:

O.K., then please let me know how current would not flow in only one direction in the following example:

Yes !

Graham

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"

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

That's an AC wave with a DC offset.

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

Again, the dispute wasn't what is conventionally or officially correct.....the original post refered to "a fully DC sine wave"....some pinhead gave a stickler reply saying..."there's no such thing as a DC sine wave" despite being provided all the actual numerical specs of the wave.....this dispute can be traced back to this pinhead's childish reply and his objection to the casual usage of the term DC (which was done, arguably, in a technical correct fashion).....

That is not always true.

Take

2) Another identical resistor of resistance R, but in series with an inductor L.

Make R=sqrt(L/C)

and put 1 and 2 in parallel and measure the impedance across that combination. The impedance is always R, and is independent of frequency.

A useless fact I would admit!!

There is no such thing as a "DC sine wave." I suspect you mean what would more correctly be described as a 10 volt peak-to-peak sine wave with a +10 volt DC offset.

The principle of superposition applies: the currents and voltages in the circuit will be the sum of those that would result if the DC voltage and the AC sine wave were applied to it seperately.

That circuit (I've fixed the link) exploits the fact that the LM139 comparator has an open-collector output. It runs off a negative rail, and cannot produce a positive output voltage.

you

communication with others.

AC-component

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

The only difference between your "DC sine wave" and an your "AC sine wave" is where you happen to choose your reference point. Most of us don't consider a wavefornm to magically shift from AC to DC simply by a change of reference.

Robert

The *pinhead* you describe was *right*.

You are describing an AC signal with a DC *component*. OR a DC signal with an AC component ! It's very easy to separate the two and analyse accordingly.

Graham

Question 1: A capacitor "capacitates" whether it sees AC or DC. An inductor "inducts" whether it sees AC or DC. A resistor resists whether it sees AC or DC. You might find it beneficial to think of what happens to each component on a component level rather than thinking of total impedance. Understand what each component does, and circuit impedance will make more sense.

Question 2: 404 file not found error That said, you can peak detect on a varying DC sine. As someone else said, its AC with a DC offset.

Ed

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......