DC Wave Questions

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.

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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.

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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

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I don't know. Look it up.

Takes a nice little vaccuum pump to do it though.

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I think he is confusing boiling with sputtering.

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