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Determine the RMS amplitude of the squarewave signal.

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    Determine the RMS amplitude of the squarewave signal.

    Came across this question on a practice test. Here is the corresponding picture and full question.

    Click image for larger version. 

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    Determine the RMS amplitude of the square wave signal, as displayed by an oscilloscope with a vertical sensitivity of 0.5 volts per division.

    The answer is 0.5V apparently, but I thought that the answer would be 0.35V. My thought process:

    The peak to peak voltage would be 1V, and the positive peak would be 0.5V. Thus if I was asked for the peak voltage, I would have stated the answer was 0.5V. Since I was asked for the RMS voltage, I instead took that 0.5V and divided it by the square root of 2, which is 0.35V.

    Am I correct, or is the test answer correct? If I am wrong, could someone please explain where I went wrong in my thought process?

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    Essentially, the RMS value is the DC equivalent value which will produce the same heating effect. The RMS value is the square root of the mean (average) value of the squared function of the instantaneous values.

    After some calculus, which you can look up if interested, a sine wave results in VRMS=VPEAK/√2

    For a square wave this results in VRMS=VPEAK

    Thinking about it in basic terms of a heating effect, you have a constant unchanging magnitude, with only polarity changing periodically, so it is a direct equivalent of a DC voltage.

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    Quote Originally Posted by Erased View Post
    Essentially, the RMS value is the DC equivalent value which will produce the same heating effect. The RMS value is the square root of the mean (average) value of the squared function of the instantaneous values.

    After some calculus, which you can look up if interested, a sine wave results in VRMS=VPEAK/√2

    For a square wave this results in VRMS=VPEAK

    Thinking about it in basic terms of a heating effect, you have a constant unchanging magnitude, with only polarity changing periodically, so it is a direct equivalent of a DC voltage.
    Ah, this makes a lot of sense. Thank you for the clarificafion!

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    Quote Originally Posted by Erased View Post
    Essentially, the RMS value is the DC equivalent value which will produce the same heating effect. The RMS value is the square root of the mean (average) value of the squared function of the instantaneous values.

    After some calculus, which you can look up if interested, a sine wave results in VRMS=VPEAK/√2

    For a square wave this results in VRMS=VPEAK

    Thinking about it in basic terms of a heating effect, you have a constant unchanging magnitude, with only polarity changing periodically, so it is a direct equivalent of a DC voltage.
    A square wave is the result of a bridge rectifier, which many technicians use to simulate DC, then smarter technicians apply a capacitor to get a smoother DC signal, even smarter techs use a regulated DC power supply.

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