Generating Harmonics from Non-linear devices

Discussion in 'Homework Help' started by Energetic, Jan 10, 2011.

  1. Energetic

    Thread Starter Member

    Jan 3, 2011
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    Hi,

    I have to show two non linear devics generating harmonics in multisim. I have managed to acheive this with a diode for one but have not managed to replicate this with an inductor, transformer, or any other supposed harmonic generating non linear device.

    I have tried various voltages, frequencies and circuits but no joy. Can anyone recommend a suitable component and at what frequency and voltage etc i will be able to see harmonics on my spectrum analyser.

    Cheers ears...
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What about an amplifier that clips?
    That will give a lot of distortion and harmonics.

    Bertus
     
    Energetic likes this.
  3. Papabravo

    Expert

    Feb 24, 2006
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    Gee I thought inductors and transformers WERE linear devices. Have I been misinformed??
     
  4. Energetic

    Thread Starter Member

    Jan 3, 2011
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    Perhaps that is one reason i've been having so much trouble with this!! My textbook states:

    Circuit elements in which the current flow is disproportionate to the applied voltage are said to have a non linear response to their inputs. These include rectifiers, diodes, transistors, valves and iron cored inductors/transformers.


    I have shown it using a transistor in the end.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When a transformer is driven into saturation, it will produce harmonics.

    Bertus
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    Yes it will, because it is a "real" component. Many simulations are done with ideal components and many "real" components are linear over some operational range.

    The definition given by the "textbook" is problematical because it defines linear in terms of a relationship between voltage and current. A reactive component can be linear in the "differential equation" sense while not having a linear relationship between voltage and current.

    Integration and differentiation are in fact linear operations. Multiplication, absolute value, dead band, and limiting are quite clearly not linear operations.
     
  7. Energetic

    Thread Starter Member

    Jan 3, 2011
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    The first two sentences are helpful, thanks, the rest is gobbledigook to me sadly. I am not yet strong enough in the ways of the force.

    I have seen a similar definition to that in several places. Why is there never just one straightforward answer in this business?
     
  8. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The key word in your textbook statement is "disproportionate". If the relationship between the applied voltage and current over the entire range of values is a constant factor then the device is linear. If not, then there is a non-linear condition.

    A voltage amplifier is linear if the output voltage waveform is a faithful reproduction of the input waveform but with a greater magnitude which is in constant proportion (related by the voltage gain) to the input magnitude.
     
  9. Georacer

    Moderator

    Nov 25, 2009
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    A clipping amplifier is a good choice for your exercise, but you could still use the transformer is you can specify a saturation current in its options and turn it into a "more realistic" device.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    It is true that if you don't know what integration and differentiation are then understanding how a capacitor or an inductor behaves will be more difficult. You should understand multiplication. Absolute value, dead band, and limiting are things you can to to a signal that produce non-linear behavior. Read up and learn.

    The answer to the last question is straightforward. Nature does not work that way.
     
  11. Energetic

    Thread Starter Member

    Jan 3, 2011
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    Just started differentiation today, brilliant fun! I will, as you say, read up and learn, but first i will go to the pub and have an ale or 3...

    Cheers!
     
  12. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    You might find that the consumption of alcohol impairs your ability to differentiate ....:rolleyes:
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    Go to bed early.
    Get up late.
    Work like hell,
    And integrate!
     
  14. Georacer

    Moderator

    Nov 25, 2009
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    Oh, no! Loosewire's gone viral! Oh, the humanity...
     
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