e
I very much doubt that he actually thinks it is literally "without limit". A few hundred amps makes a very big mess of things.
The voltage drop on an arc of constant length does decrease as the current increases. The rate of decrease slows at higher currents. At extremely high currents, the size of the plasma ball will suddenly decrease as will the voltage as a black hole is formed. This usually leads to the end of the universe.
Oh, don't be a PITA.
John
Argument?
John
Which is exactly why it's a good idea to connect an iron in series.
John
Or, more succinctly:
Negative resistance From Wikipedia, the free encyclopedia (Redirected from Negative differential resistance)
He probably assumed that it was obvious. I've heard the term used occasionally (e.g. w.r.t. tunnel diodes or UJTs), and I've never seen anyone feel the need to add the "differential" or "slope" part.
Sure it would (unless you genuinely believe that, by "without limit", he was claiming that the current would rise to infinity).
For a constant supply voltage, positive resistance results in negative feedback and stable equilibrium, while negative resistance results in positive feedback and unstable equilibrium.
Now _that's_ being picky. "Has negative resistance" is commonly understood (by folks who could understand in the first place) to include systems that have a negative slope somewhere in it's i vs. v curve.
_Since_ you're being so picky, they'll have an I vs. V relationship to which the term "resistance" doesn't really apply.
Not so. At least not in the real systems that I know of. There may be a
1:1 arc current vs. voltage drop relationship, which _should_ be an equilibrium point, but it'll be dynamically unstable, leading either to an arc that won't sustain or one that goes to high currents quickly. Ballasting it with sufficient series impedance such as a resistor (or an inductor in an AC system) will make for a steady arc. (Note that ballasting it with _insufficient_ series resistance will give you two equilibrium points, one stable, one not).For a graphical explanation, see p 32 of "Fundamental Electronics and Vacuum Tubes", by Arthur L. Albert, Macmillan 1947 (sorry, no ISBN :-).
If you know of a real, working system that makes this work by controlling the voltage at the arc I'd love to expand my knowledge.
-- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
I hate it when that happens.
Then howcome it's been called "negative resistance" since as long as I can remember, but today is the first time I've ever heard the term "negative resistance slope"?
Thanks, Rich
While it's blowing, yes.
Hope This Helps! Rich
What argument? Negative resistance has been "negative resistance" since the invention of the arc.
What planet have you been on for the last 100 or so years?
Thanks, Rich
Why do you call this a "view"? The facts are, the arc will conduct as much current as the universe can supply. Maybe you mean "It wouldn't be 'without limit' because the power plant would melt" or some such, but that's not a limitation of the arc.
Quit being a PITA.
Thanks, Rich
I made a carbon arc one time with "D" cell carbons, and Mom's iron in series. I just wired the whole iron in series, so when it got to the hottest setting, it turned itself off. Later, after I had moved out and bought my own iron, one of the guys in the dorm borrowed it, bypassed the thermostat, and melted my iron. )-;
Cheers! Rich
...except that he is not.
Seems a bit of PKB going on here.
Why not?
Perhaps. It seems to be snipe season around these parts.
When AlwaysWrong is "right", you'd better rethink your position.
In article , snipped-for-privacy@austininstruments.com says...>
Why, thank you! I love you too.
To be consistent with Sylvia* you'd have to say positive resistance slope instead of resistance.
*But it's nice to see a girlie around here.-- Reply in group, but if emailing add one more zero, and remove the last word.
I work on 3 foot long argon arcs with up to 65 amps and 560V across them, using hot cathodes. Most of the time it has a positive slope. Ie, I increase current 1 amp, the voltage across the tube goes up about half a volt. However The I/V line is not always flat, and does not always have a positive slope. In fact, it depends the gas pressure. For low pressure arcs, there is a place on the graph known as the inversion point where you pass through that region and the tube voltage starts to go down with respect to current increasing. We can tell where the tube is in its lifetime curve by sweeping the current and seeing where inversion starts. Tubes that have gas buried in the tube walls from years of operation will start showing the inversion earlier as you turn the current down.
A common design for a large frame argon ion laser specified minus 7 ohms as the design impedance for the power supply to counteract.
Steve
Ever heard the Lenny Bruce routine?
"... f*ck you Mom, f*ck you Dad..." ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
Stop being practical and making sense and using plain English. That's not allowed on usenet!
John
The high-power CW (ie, not damped-wave) transmitters in the early days, before big power tubes, were interesting. Both Poulsen arcs and Alexanderson alternators could generate hundreds of kilowatts in the VLF range.
Why squabble like spoiled kids, when there's so much interesting stuff out there?
John
Yep. Girls can be smart, too!
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
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