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Electrical friction?

G

George Herold

Jan 1, 1970
0
So the thread by Vlad about the Johnson noise of magnetic core losses got me thinking about other types of damping. And I was wondering if there is an electrical equivalent of friction? It seems to me that it could be a constant voltage loss. So maybe just some diodes in an LC circuit?

It seems to work, here’s a spice file.
Any thoughts or other ideas are welcome.
(Something that worked at less than 100 V would be nice.)

George H.

Version 4
SHEET 1 1012 680
WIRE 144 -592 -48 -592
WIRE -48 -560 -48 -592
WIRE 288 -464 192 -464
WIRE -48 -432 -48 -480
WIRE 400 -432 320 -432
WIRE 544 -432 464 -432
WIRE 288 -416 288 -464
WIRE 144 -384 144 -592
WIRE 192 -384 192 -464
WIRE 0 -336 -224 -336
WIRE 128 -336 80 -336
WIRE 288 -336 208 -336
WIRE 320 -336 320 -432
WIRE 320 -336 288 -336
WIRE 400 -336 320 -336
WIRE 544 -336 544 -432
WIRE 544 -336 464 -336
WIRE -224 -288 -224 -336
WIRE 544 -256 544 -336
WIRE 288 -240 288 -336
WIRE -224 -144 -224 -208
WIRE 288 -144 288 -176
WIRE 288 -144 -224 -144
WIRE 544 -144 544 -176
WIRE 544 -144 288 -144
WIRE 288 -112 288 -144
FLAG -48 -432 0
FLAG 288 -112 0
FLAG 288 -416 0
SYMBOL voltage -48 -576 R0
WINDOW 0 -74 28 Left 2
WINDOW 3 -235 -36 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 5 0 1n 1n 1 200 1)
SYMBOL res 96 -352 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 1
SYMBOL cap 272 -240 R0
WINDOW 3 27 56 Left 2
SYMATTR InstName C11
SYMATTR Value 1m
SYMBOL ind 528 -272 R0
WINDOW 0 30 34 Left 2
SYMATTR InstName L1
SYMATTR Value 1m
SYMBOL sw 224 -336 R90
SYMATTR InstName S1
SYMATTR Value MYSW
SYMBOL voltage -224 -304 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 1000
SYMBOL diode 464 -352 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D1
SYMBOL diode 400 -416 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
TEXT -200 -32 Left 2 !.tran 0 2 .9 1m
TEXT 64 -32 Left 2 !.model MYSW SW(Ron=1 Roff=1Meg Vt=.5 Vh=-.4)
 
S

Sylvia Else

Jan 1, 1970
0
With friction (in its ideal form), there is no movement until the
applied force reaches some threshold, and then there is acceleration
that is proportional to the applied force minus the threshold force.

If we consider the voltage to be the force, and current to be the
velocity, then the behaviour is nothing like resistance.

It is, however, like a simplified diode (constant, but non-zero, forward
voltage drop) in series with an inductor.

Sylvia.
 
J

John S

Jan 1, 1970
0
With friction (in its ideal form), there is no movement until the
applied force reaches some threshold, and then there is acceleration
that is proportional to the applied force minus the threshold force.

If we consider the voltage to be the force, and current to be the
velocity, then the behaviour is nothing like resistance.

In the sense that heat is produced as a result of both, it is not
"nothing like resistance".
 
R

Robert Macy

Jan 1, 1970
0
With friction (in its ideal form), there is no movement until the
applied force reaches some threshold, and then there is acceleration
that is proportional to the applied force minus the threshold force.

If we consider the voltage to be the force, and current to be the
velocity, then the behaviour is nothing like resistance.

It is, however, like a simplified diode (constant, but non-zero, forward
voltage drop) in series with an inductor.

Sylvia.

I posted an answer to George a few hours ago, didn't see it.

What I had was ...one model of motion is
force is voltage
mass is inductance
damping is resistance
drag from turbulence is ???
stored energy, spring [from memory also height] is capacitance
friction is a reverse voltage, subtracted from applied force
stiction is a spike reverse voltage

A diode is allegorically more like 'slop' or backlash, because NO force is applied until the friction is overcome. Friction is a bit more like voltage of the opposite polarity to whatever is being applied.

Wait. same, forget it.
 
K

Klaus Kragelund

Jan 1, 1970
0
So the thread by Vlad about the Johnson noise of magnetic core losses gotme thinking about other types of damping. And I was wondering if there isan electrical equivalent of friction? It seems to me that it could be a constant voltage loss. So maybe just some diodes in an LC circuit?



It seems to work, here’s a spice file.

Any thoughts or other ideas are welcome.

(Something that worked at less than 100 V would be nice.)
[Snip]

What would be the point of knowing the equivalent to friction in electronics?

Regards

Klaus
 
G

George Herold

Jan 1, 1970
0
--- I believe it's called 'resistance'. -- JF

Hi John, friction is actually a little different from resistance.
I tend to think about it in terms of simple harmonic motion, so if you'll forgive the digression for a moment. For an LCR circuit the voltage going around the loop is, (Forgive me if I get the some signs wrong.. I mostly want to look at the units involved.)
C * q(t) + R * dq(t)/dt + L dq(t)^2/dt^2.
And for a mechanical system (with no friction, but with a velocity dependent ‘dash pot’. (gamma)) (mass M on a spring k.)

k * x(t) + gamma * dx(t)/dt + M dx(t)^2/dt^2

So both give harmonic motion. And we make the mapping of charge to distance,
So
x ->q
velocity -> current

Now friction gives a loss that is proportional to the distance traveled, where as resistance goes as current, which equates with the velocity.

So I was thinking that ‘electrical’ friction would look like some loss that went with the charge. (Sorry my thinking here is still a bit fuzzy.) I didn’t know how to do that, but the voltage on the cap is proportionalto the charge... So I was thinking of a constant voltage loss.. an ‘ideal’ diode. (And by ‘ideal’ I mean the freshman level of ideal.. no conduction till some voltage and then perfect conduction after that.)

If you scroll down this page till almost the bottom, you get to damped oscillations, you’ll see three plots, the first for friction, then velocity dependent damping (LCR) and the v^2.

http://www.teachspin.com/instruments/tho/experiments.shtml

The diode LC circuit looked like the friction damping... the decay is linear in time.

George H. (Sorry for the long relpy)
 
G

George Herold

Jan 1, 1970
0
Yeah something like that... I had two diodes in parallel (one reversed)

George H.
 
G

George Herold

Jan 1, 1970
0
Ahh, Well I can think of a few reasons (mostly self-centric). I guess the simplist is that it would help with the mechanical and electrical analogies..

Hey! All those analog computers that were used in the past for simulating mechanical systems.. they must have know how to do friction... I'll try googling that.

George H.
 
G

George Herold

Jan 1, 1970
0
They are cool parts, on account of the friction analogy.

OK thanks, I'll see if I can make those work too.

George H.

-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
 
J

JW

Jan 1, 1970
0
What's with the non-paragraph, non-wrap?

Using Outhouse Excuse ?:-}

...Jim Thompson

You're using Agent. If you press "H" you will see the headers and see that
it's GoogleGroups. Every day it becomes more broken...
 
G

George Herold

Jan 1, 1970
0
What's with the non-paragraph, non-wrap?



Using Outhouse Excuse ?:-}

Sorry Jim, f*ing google groups I'm afraid. So when I use chrome google puts in all these extra lines.
Today I tried with IE. No extra lines.. but it globs the whole thing together.

George H.
 
G

George Herold

Jan 1, 1970
0
Try an ideal-diode bridge rectifier driving a negative current source, sothat
the diodes conduct by default. That is an ideal bipolar current sink, the
equivalent of friction. Even a real diode bridge and a current source would be
good down to a couple tenths of a volt, and go ohmic below that.
OK. (oops I drew a ring diode first.) How the bleep does current get through the bridge. Or is that what the current source is for.
I drew this,

Sig in/ out.
|
.--|>|--+--|>|--.
| |
gnd-+ +-->current sink
| |
.--|>|--+--|>|--.
|
Sig in/out

I don't think that's going to work though.

Not to worry I'll play with it over the weekend. This is only 'for fun'.

George H.
 
J

John S

Jan 1, 1970
0
Did more than one of us sleep through physics class?

http://en.wikipedia.org/wiki/Friction#Static_friction

The kind of viscous friction that you describe (for lack of a better
term) is virtually unheard of in the real world. In the real world, one
always sees Colombic friction (Wikipedia's "kinetic" friction) and nearly
always stiction.

While one can argue that the Wikipudlians don't always get things right,
this article is certainly in line with my experience making motors and
other motion control systems behave correctly, and with various articles
that I have read, both by control wonks and by tribologists.

When I went through physics in the early 60's, they did not call it
stiction. It was called static coefficient of friction as opposed to
dynamic coefficient of friction.
 
G

George Herold

Jan 1, 1970
0
The current source has to float.
Ahh, ok I was wondering if I could float a current source? ...
No don't tell me.. I must be able to make something out of opamps.
Try this. Note that the ringing decay is linear, not exponential. This
(I'll check out your spice file later.)
is friction, not viscosity like a regular resistor. It's a cool

concept; thanks for introducing it.
Ahh.. well Vald started it with core losses.
Friction seems weird though... it's got a 'scale' the size of the loss,
where as resistance is linear, ..all the way down...
(I'm trying to channel Terry Pratchet, "Elephants all the way down...")
There must be deep physical issues here. Does a fristor have Johnson
Seems like some analog computer guy must have done friction long ago.
noise? Its unit of measurement is amperes, not ohms.

I don't have any use for this idea. But that's ok. Maybe I'll understand regular friction better. I guess you could damp a resonance against small signals, but still ring for a while on big stuff.<snipping double spaced spice file.. see previous post>

George H.
 
G

George Herold

Jan 1, 1970
0
When I went through physics in the early 60's, they did not call it

stiction. It was called static coefficient of friction as opposed to

dynamic coefficient of friction.

So (I think) I'm talking about an electrical analog of dynamic friction.
Though the spice file I posted looks much more like static friction, big step changes where the current goes to zero. Maybe they are not all that different in terms of energy loss. (For a resonant circuit.)

George H.
 
G

George Herold

Jan 1, 1970
0
On 7/13/2013 2:11 PM, Phil Hobbs wrote:

<snip previous stuff.>

That's totally great! I might have to bog one together. It'd make a cool 'scope shot if nothing else.

George H.
 
There must be deep physical issues here. Does a fristor have
Johnson noise? Its unit of measurement is amperes, not ohms.

There is a generalization of the fluctuation-dissipation
theorem due to Stratonovich. It's probably applicable.

An interesting concept, this 'fristor'.

Regards,
Mikko
 
R

Robert Baer

Jan 1, 1970
0
There is a generalization of the fluctuation-dissipation
theorem due to Stratonovich. It's probably applicable.

An interesting concept, this 'fristor'.

Regards,
Mikko
Ever hear of hot electrons?
 
Ever hear of hot electrons?

In some meanings, I have. Like hot-electron bolometers, or
hot-electron effects in SQUID shunt resistors. Any electron
which is far from thermal equilibrium qualifies, I suppose.

But I'm puzzled about why do you ask?

Regards,
Mikko
 
R

Robert Baer

Jan 1, 1970
0
In some meanings, I have. Like hot-electron bolometers, or
hot-electron effects in SQUID shunt resistors. Any electron
which is far from thermal equilibrium qualifies, I suppose.

But I'm puzzled about why do you ask?

Regards,
Mikko
The topic was "electrical friction"...
 
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