DC Wave Questions

apparently you have not seen the equations governing reactance to make the statements you do about

deh said

zero-

to zero.

fld said

nor have you ever designed a switch carrying power loads, to say that in non-DC rated switches, arc quenching does not rely on current reversal. Or to ground fault design, I might add.

deh said

do

fld said

As I said, your position works only if you are in one corner of one part of all electrical phenomena, and if you use technicians tools rather than engineers and scientists tools.

You will just have to live with what the big boys > >"Floyd L. Davids> >> > Strictly speaking, I believe the reactance (part of impedance)

appropriate

variation".

and

by

the

direction

purpose.

have

you really don't know much about power switches, do you?

to

the

and

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do

views

see

Dr. Polemic wrote in news: snipped-for-privacy@4ax.com:

Yea, I'd have to call BS on that one...

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Your descriptions apply to *your* comments, not mine!

zero.

So your one single point of exposure defines the entire field?

I don't think so at all. You are trying to say that specific instance is the general case. I was saying that it isn't, and that the general case is *much* larger.

That describes *your* position very well!

Actually, getting too deep into either one, or into any single field in either one, is what causes these assumptions like yours, that specific instances are the entire general case.

One of the problems with academia, for example, is this specialization. Whereas someone who works in the field runs into whatever each project coughs up. The exposure is significantly greater. And no that does not mean that academics is bad, wrong, poor, unnecessary, less that useful or any other silly thing you are likely to try twisting it into. It does mean that it necessarily, for any one individual, has a narrower scope, and people with field experience have a broader view, generally (which also often lacks as much depth too). Both are necessary.

Well, I certainly do lack depth in that particular subject! But knowing about power switches doesn't define understanding AC vs DC, even if that is your field of expertise. In fact, it might be the cause of your confusion.

Power switches may in fact operate at the moment of direction reversal, but that is merely one specific example of the broader "relative to the static state" general description that I gave. The switch can happen at any time there is no current flow (or rather, when the phase angle and rate of change is appropriate) across the "contacts". But that can be at some DC potential which is equal on both sides of the switch, or at a zero voltage, either of which is *not* at a current direction reversal. Maybe those circumstances don't happen with AC distribution power switching, but they most certainly do in other fields.

The requirement is *not* that a direction reversal be taking place. That is just a collateral circumstance that happens to exist in AC power distribution systems at the same time the necessary phase relationship exists.

The very same general principle is used in video switching... except not at a time when there is any change in current direction!

Floyd L. Davidson wrote: (snip)

Unless it is a solid. Then it sublimates. Boiling only happens to liquids.

think gold will

evaporate, though;

What he said was: "Danged, several weeks of work shot because it just hadn't occurred to him that ni-cad would boil at room temperature." I suppose I could say that tungsten exaporates at room temperature and then say that I didn't say that the filament wan't held at room temperature; I just meant that the room was at room temperature.

--- As John Popelish remarked, boiling is only possible if the medium in which the boiling is occurring is a liquid, so if the water has turned into ice at 0°C, sublimation is the mechanism which water molecules will use to evaporate from their parent structure.

Since this a technical forum and we _do_ have ground rules, I believe we generally agree that, unless otherwise specified, standard pressure is defined as 760 millimeters of mercury and standard temperature is defined as zero degrees celcius. While the boiling point of water is dependent on pressure, the freezing point, I believe, is not.

At least, not to a great extent. I don't have any data to support that position, but I'd love to see some, if it's out there.

-- John Fields Professional Circuit Designer

Handbook of Chemistry and Physics, Twenty Fifth Edition, Table p.1696.

All you have to do is go ice skating! You skate on a thin layer of water, produced by the pressure of the skates. Water is also one of the few liquids that expands when it freezes, which is fortunate for life on this earth! :-)

I believe that in this forum we assume temperature is a variable that must be accommodated in design, unless otherwise stated. I cannot imagine why any unstated temperature would be assumed to be 0 oC. I suppose sea-level atmospheric pressure is often assumed, but where it matters, it should not be assumed at all.

You might want to consider the "triple point" of water, below which pressure "melting point" is meaningless and the "freezing point" varies considerably with pressure.

See:

are? And

There seems to be a consensus that, since no signal is absolutely stable with time, then DC must not exist. That does simplify life.

John

Using the usual meaning of "freezing" which is the transition from liquid to solid, that graph shows "freezing" occurring at 273K over a million to one range in pressure. I would say that the statement "While the boiling point of water is dependent on pressure, the freezing point, I believe, is not" is essentially true- to all except a nitwit like you.

Atta boy, Kevin. Ratch

solid, that graph shows "freezing" occurring at 273K

It does not. The straight part of the liquid/solid phase boundary covers less than 5 orders of magnitude. "Over a million to one" would be more than 6 orders of magnitude.

on pressure, the freezing point, I believe, is not"

In a discussion that has involved sublimation, to exclude that part of the phase space would be essentially silly.

Off your meds again, Fred? I expect you to be more careful with your graph reading before breaking into your frothing-at-the-mouth modes.

...

What happened to the ground rules you mentioned? Being correct isn't one of them?

Tell us more about AC, so we can laugh again. Then come back to this, for more!

What's the matter John, are you bitter that several people, who do understand the theory and practice, have said you are wrong...

John Fields wrote: (snip)

If you are willing to consider extreme conditions, not only does the freezing point change, but there are many ice phases, each structurally distinct and with temperature and pressure boundaries.

Ladies and Gentlemen--jackbruce9 has left the building. ;-))

Tut

DIE THREAD!!!!!!!

Didn't see this response, so piggy-backing my reply.

There are literally hundreds of references on the web about DC, AC and Transient Analyses. Browse some of the simpler overviews, and you will see that the mathematical differences are clearly defined, and that's what it's all about. The math determines the signal type. It is my belief that the widespread disagreement is due to participants that just like to argue a lot.