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Multisim Transient Analysis for LC parallell circuit

  1. Feb 26, 2013 #1
    1. The problem statement, all variables and given/known data

    The main problem is that I need help using Multisim for transient analysis of a simple LC parallell circuit. I am doing something wrong.

    C= 3*10^-5 F
    L= 3*10^-3 H

    The Capacitor is charged to 10V

    What happens to the energy of the capacitor when we connect it in parallel with the inductor. Trace the voltage of the parallel connection and the current of the inductor until about 2ms after connecting.

    Use Simulink.


    2. Relevant equations

    T=2*pi*sqrt(LC) = 1.89 ms

    f= 1/T = 1/(2*pi*sqrt(LC)) = 531 Hz

    3. The attempt at a solution

    I have created this circuit:

    31G6nWe.jpg

    I suspect something is wrong already here, because the program will not let me rename nets.

    sjX2ecH.jpg

    "Preferred net name cannot be modified when a global connector is in connection to the net."


    I go to:
    Simulate->Analyses->Transient Analysis

    I set the stop time to about 5 periods. 0.01s.

    Now.. why is there no voltage variable for either component?

    U5o5SF7.jpg

    I add I(L1) and simulate.

    W1BH4qQ.jpg

    Can somebody please point out where I am going wrong..? I am sure there are multiple mistakes, I am not too good with Multisim yet.
     
  2. jcsd
  3. Feb 26, 2013 #2

    gneill

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    Staff: Mentor

    I'm not familiar with the details of using Multisim, but it appears to me that your circuit has both ends of both components shorted together and grounded. I can't imagine getting any reasonable results from that.

    Try eliminating one or the other of the paths to ground.
     
  4. Feb 26, 2013 #3
    Alright, I added a battery with no output, and now I can measure more things, but even if I only select the current through the inductor I get a flat graph.

    9Ebnw56.jpg
    TRLmVh5.jpg
     
  5. Feb 26, 2013 #4

    gneill

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    Staff: Mentor

    Eliminate the battery. Eliminate the wire. NO connection.
     
  6. Feb 26, 2013 #5
    But.. aren't they in series now..?

    LiHnd5H.jpg
     
  7. Feb 26, 2013 #6

    gneill

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    Staff: Mentor

    With only two components, there is no distinction between series and parallel connection.
     
  8. Feb 26, 2013 #7
    Bingo. That's what I thought, but since the task specified parallel I tried to come up with something.

    The problem with the current graph being flat is still there, would love for some Multisim advice on this!

    Thanks for the help thus far!
     
  9. Feb 26, 2013 #8

    gneill

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    Staff: Mentor

    I'll see if I can find someone who knows Multisim to have a look-in.
     
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