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Homework Help: Finding RMS value of strange column function

  1. Dec 8, 2011 #1
    1. The problem statement, all variables and given/known data
    This is the given function:
    RMS.png


    2. Relevant equations
    The RMS equation goes like this:
    [tex]
    \sqrt(\frac{\int(f(t)^2 dt)}{b - a})
    [/tex]


    3. The attempt at a solution

    The first part of the exercise was to find the mean value.
    This is A/4.

    The RMS value should be higher than the mean value, but I need the function to use the equation and I can't "see it" from the picture.
     
  2. jcsd
  3. Dec 8, 2011 #2

    NascentOxygen

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    Staff: Mentor

    RMS == the square root of the average of ( the square of the signal).

    You are given a graph of the signal. On the same axes you can plot the signal squared, then determine the average of this. Then ...
     
  4. Dec 8, 2011 #3
    Ah, thank you for putting it into perspective

    RMS value = A/2
     
  5. Dec 8, 2011 #4

    NascentOxygen

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    And it's not called a strange column function. It's called pulsed DC. Or 25% duty cycle switched DC. :smile:
     
  6. Dec 8, 2011 #5
    duly noted ^^
     
  7. Dec 8, 2011 #6
    And what happends if the "pulsed DC" varies between +1 and -1 V ? The signal squared = 1V anyhow (except for a few 0V periods)

    rms2.png
     
    Last edited: Dec 8, 2011
  8. Dec 8, 2011 #7
    Never mind. I got it :)

    I made it too complicated at first
     
  9. Dec 8, 2011 #8

    NascentOxygen

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    Then it's called a strange column function.

    What you have sketched doesn't tally with your verbal description. For what you sketched, its RMS value will be equal to that of a 60% duty cycle switched DC, since a level of -1 contributes the same as does +1, in determining RMS value.
     
  10. Dec 8, 2011 #9
    the second picture is another problem which I had to determine the mean and RMS value.

    the problem description does not mention any DC or functional description of the graph
     
  11. Dec 9, 2011 #10

    NascentOxygen

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    Staff: Mentor

    You could call it a stepped waveform. Maybe a staircase.
     
  12. Dec 9, 2011 #11
    I'll keep that it mind, thanks :)
     
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