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Electrical friction?

Discussion in 'Electronic Design' started by George Herold, Jul 11, 2013.

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  1. 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
    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)
  2. Sylvia Else

    Sylvia Else Guest

    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.

  3. John S

    John S Guest

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

    Robert Macy Guest

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

    What I had was 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.
  5. [Snip]

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


  6. --- 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,
    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.

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

    George H. (Sorry for the long relpy)
  7. Yeah something like that... I had two diodes in parallel (one reversed)

    George H.
  8. 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.
  9. 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 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
  10. JW

    JW Guest

    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...
  13. John S

    John S Guest

    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.
  14. 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.
    (I'll check out your spice file later.)
    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...")
    Seems like some analog computer guy must have done friction long ago.
    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.
  15. 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.
  16. <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.
  17. Guest

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

    An interesting concept, this 'fristor'.

  18. Robert Baer

    Robert Baer Guest

    Ever hear of hot electrons?
  19. Guest

    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?

  20. Robert Baer

    Robert Baer Guest

    The topic was "electrical friction"...
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