a question about resistors in an arc experiment

Then how does it make your life better to anoint yourself arbiter of it?

Thanks, Rich

I have no power to be an arbiter; what gave you the idea that I do?

But I can certainly have personal preferences and opinions, just as you do. And in an electronics newsgroup, I prefer the electronics to be right.

John

And it would be a good counter, if what you had provided actually looked like a negative resistance in that situation. But it doesn't. Measure the current going in, and you'll find it's positive - that is, that the circuit presents a positive resistance, not a negative one.

Sylvia.

We're not talking about a negative resistance characteristic in this subthread. We're talking about total negative resistance.

Sylvia.

I don't see why a negative resistor would do that. Of course, we have the problem of hypothesising a physcial mechanism for something we're pretty sure can't exist anyway, but to the extent we can think past that obstacle, I can't see why an unattached negative resistor wouldn't just lie there quietly with no voltage and no current.

Sylvia.

In a noiseless world it would. But if somehow its terminal voltage got to be any amount nonzero, no matter how small, it would begin to source current in the direction such as to reinforce that voltage, and awwwwway we go. Any thermal or quantum fluctuation would be enough to set it off.

Spice will allow perfectly noiseless positive-feedback states to persist forever, for want of a direction to go in, the equivalent of a pencil balanced on its point for a zillion years. One sometimes has to poke in a tiny initial condition to shake things up.

Oh, I was wrong about the first circuit not working. It is a different kind of negative resistance, one that accepts a current drive and reacts with a "backwards" voltage response, but goes bonkers if driven by a voltage source. The second circuit is stable if driven by a voltage source, and reacts with a negative current, but explodes if you leave it open. Both dump power *into* the source.

Just tried it in Lt Spice. A -10 ohm resistor in parallel with a 1F capacitor will sit quietly forever. But goose it with a really tiny current pulse, just once, and the voltage takes off exponentially. Cool. LT Spice seems to use the second type negative resistor.

I still can't get my head around the fundamental reason why there's only one kind of positive resistor but two kinds of negative resistor.

John

Spice has numerical noise that often starts oscillators. Here is a Yahoo LTspice post from Helmut that describes it a bit more:

Hello Dieter,

Yes. SPICE doesn't simulate noise in a .tran analysis. It's often only the numerical "noise" in SPICE which starts the oscillation of crystal oscillators.

Maybe you want read a little bit about simulation of crystal oscillators.

Best regards, Helmut

Maybe. But that's a lot of time to spend on a newsgroup post.

What I'd like to do is highlight, right-click, see the schematic, run.

John

So you really don't know the direction of the current. Bad.

The HELP doesn't even seem to mention current probing.

John

On Jan 19, 6:37=A0pm, John Larkin wrote: [....]

I think I can add to the confusion:

We are thinking "number line like this:

-3, -2, -1, 0, 1, 2, 3, ..... really big, infinite, -really big ...

There are two ways to get to a negative number. One takes you past the "infinite" value. In truth though. we have a 2D world we can avoid hitting the singular value by going a little reactive.

................................. .................----------...... ..-...0...-------....*.....------ ...-------....................... .................................

As often happens in math, the pole is the center pole of a spiral staircase. You have to go around the pole twice to get back where you started.

I use MacroExpress to handle repetitive exercises like that.

...Jim Thompson

If there is a binary format version of the save file as opposed to ASCII, that binary can be posted in abse.

Don't you remember how much grief certain parties gave me for using the term "infinite"?

(I don't know why I call them parties, when they never seem to have any fun.)

John

You're a Crappy Headed Ho. Don't make up affectionate nicknames for my dick. You have already been told NO.

You must have me confused with someone else.

I have never posted a circuit here, much less a non-working circuit.

"ones"? Are you getting old and senile like The Donkey did now, Johnny? Ease up, Chuck... You make me want to Up-Chuck.

Be a Pro, not a ho. Tho your head ain't nappy, your brain sure is crappy.

If you touched some of my circuits, you'd be gettin' zappy.

Why is it that YOU are the only one that makes use of the term then, Johnny?

But it's so tiny and helpless! Makes everybody feel sorry for the poor little thing.

Ah, poetic too. Charming.

John

Are you negatively resisting his attempt at a retort? :-]

Because I'm too polite to use the words you use?

John