DC Wave Questions

I simply feel it's prudent to carefully consider all responses, as I've grown rather un-fond of the taste of my foot in my mouth. I agree that the poster's attitude is obtuse at best, but flinging off-hand insults is risky. I should know.

Besides, right now I'm the new guy in a new job after 30 years in electronics, so I have to practice restraint. Practice, practice, practice! :-)

And purity and other factors.

I've been following the many discussions that evolved from the OP's original post, and I must congratulate both of you, kinyo and daestrom, for opening your minds a little (not too much, lest reality set in and you realize that you are/were, in fact, at work) and being the most helpful in terms of answering the OP's original question.

Now, I have no formal education* in electronics, having learned by reading and the tried and true method of trial and error (mostly error :) ). All the books, magazines, and various other sources of information on electricity and electronics define AC as a _CURRENT_ that periodically reverses direction and DC is a _CURRENT_ that does not change direction, as many of the other posters have stated.

Now, yes, I agree that "DC sine wave" is not a proper description, but when I first read it, I took it to mean Direct _CURRENT_ (as opposed to one that takes the scenic routes) with a voltage that varies in a sine wave like manner. "10VDC with a 5V p-p waveform superimposed" is, IMO, the most descriptive.

• Not 100% correct. My advanced training in the US Army was in the electronics field as a front-line troubleshooter, basically a "box swapper." Although I did not receive board-level repair training, I did have to endure seven months of theory ranging from the basic theory of electricity and electronics, through R, L, and C (and ELI the ICEman), tubes (yes, we were taught how they worked; seems tubes are not affected by the EMF pulse generated by a nuclear bomb blast) and transistors, amps and such, RF and radio, digital electronics theory, basic digital circuits, and on up through computer basics and operation.

Heck, we troubleshooted (trouble-shot?) an entire system on paper, as the trainer was not available to us. We used laminated drawings of the equipment panels, and used dry erase markers to indicate switch positions and indicator status. Try _that_ sometime.

Now for the "not 100% correct" part. Our class leader, a sergeant, had previous training on similar equipment in a different MOS... er... job. I held a class average roughly 0.5 point below his for the theory part of the course, as I already knew _MOST_ of the basics (I only had a 94 average for the basics). Made him look a bit bad, though. The last two months of the nine-month course was hands on troubleshooting, basically find the bad box and swap it out, or find the bad cable/connection/etc. and fix it. Ol' Sarge clobbered me here, as in my hobby I had never done troubleshooting on this scale (I'd only done troubleshooting on the simple circuit boards I'd made at home previous to my enlistment). I did learn a lot, though. Now if I could just remember exactly what it was I learned those years ago.:)

Peace and Long Life.

RoyalHeart

The difficulty is understanding just what Don was getting at. His first post in its entirety was:

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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.

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--------------------------------- "AC" or "DC" are gross and meaningless oversimplifications.

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If he thinks "AC" and "DC" are gross and meaningless oversimplifications, why would he offer alternative definitions of AC and DC to those given by Penoyer which Don thinks are "Total and utter horseshit"? Why offer definitions of AC and DC at all if he thinks so poorly of the terms? Because when people see him first disparaging someone else's definitions and then offering definitions of his own, they're going to think he believes his own definitions are good ones.

On Mon, 13 Jun 2005 21:28:49 -0500, operator jay wrote: [snip]

There are really only two definitions put forth in this thread. One is that AC refers to all non-zero frequency components of a signal, and DC refers to the zero frequency (average) component of a signal.

The other camp believes that DC means a current whose direction doesn't change, and AC means a current whose direction does change.

For me, the fact that a Voltage can be called DC proves that the other camp is not right, or not entirely right. In fact, the OP was talking about a DC Voltage. There was no mention of current at all.

--Mac

When the context is clear, people sometimes use the same word (especially, informally) to mean one of several different things in different contexts. The problem with the original post was that the poster meant the opposite of what most of us would have assumed the context implied, so we tried to explain that to him. Then he told us either we were wrong or that it didn't matter, if we were capable of figuring out what he meant. Some people are harder to help than others. ;-)

Not to mention with *what* it is!

I knew a fellow one time who put together a nice little experiment where he bolted everything together with nice shiny nickel-cadmium plated screws.

He then proceeded to boil the ni-cad coating off the screws, which plated the expensive ceramic insulators and shorted out his thermionic diode.

Danged, several weeks of work shot because it just hadn't occurred to him that ni-cad would boil at room temperature.

He eventually made it work though, using stainless steel hardware, and when he wrote a thesis about what his diode did and didn't do, they awarded him a PhD in Nuclear Engineering.

I doubt that it *boils* at room temperature; evaporates slowly, maybe. At least, not at the temperature of any rooms I've been in.

Horse pucky. I think I can afford to miss the tutorials on your website.

least, not at

Oh, it boiled off! Damned fast too! And no, you wouldn't fit into the 18" vacuum jar this was in.

The way to get ni-cad to boil at room temperature is simply reduce the pressure to something significantly below its vapor pressure. We did it knowingly with gold too once, and that was nothing short of beautiful as far as the results went. The entire inside of the bell jar was very faintly plated with gold. That particular experiment was testing the voltage breakdown of ceramic wafers, so in addition to the gold plating there was the bluish white glow from a high voltage arc too. Really great visual effects!

That was 40 years ago...

Pure DC, or something close to it, is actually pretty rare stuff.

Even on battery power plants, which are extremely good filters, there is some AC on the leads of just about anything powered from the battery unless either the battery or the load is all but embedded in the other.

For example, the 48 volt battery plants that telephone companies have, use some rather large cables to supply voltage to equipment. Yet a filter is required at every fuse bay to decouple the AC noise on the supply cable from the equipment in the bay. Even then, the supply lines have an astounding amount of AC noise on them.

That was particularly true back in the days of mechanical switches, when a telco switch was filled with "DC" switched lines that had mechanical contacts, and most of the loads being switched were inductive.

There is even more of the same going on in modern digital switching systems, minus the inductive kick, but those are filtered much more effectively because unlike the old mechanical monster, these new ones will malfunction themselves if the noise isn't filtered out.

And is pretty cold - ask Thevenin.

least, not at

So, tell me, what is the vapor pressure of Cadmium at 20 degrees C?

--- Nickel-cadmium usually refers to the metals used in fabricating a family of secondary cells used in redchargeable batteries, while cadmium, by itself, was once used to plate mechanical fasteners. It has dropped out of favor and its use may now be prohibited for that purpose due to its toxicity and effect on the environment.

-- John Fields Professional Circuit Designer

So, the first Fourier term is always zero. Got it.

Damn, this thread will hit 200 posts soon. The less the content, the bigger the thread.

John

No, the "intrinsic" _meaning_ (in case you'd care to check the original post) of "boiling" or "freezing" doesn't change, no matter what the temperature and pressure you're applying.

You're confusing _meaning_ with _parameters_. I have seen water freeze and boil simultaneously in a single container. Anybody can do this - just get a decent bell jar and a good vacuum pump. The "boiling point" certainly changes with ambient pressure, but that does not change the intrinsic nature of _what boiling is_. I think this might have been Mike Berger's point here.

Thanks, Rich

He has tutorials? You've got to be kidding.

John

least, not at

I don't know. Look it up.

Takes a nice little vaccuum pump to do it though.

least, not at