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Calculating RMS Value of a 2V Amplitude, 2s Period, 50% Duty Cycle Square Wave

elektrokiler 27056 11
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How do I calculate the RMS value of a 2 V square wave with a 2 s period and 50% duty cycle?

The RMS value is 1.41 V, not 1 V. For a 50% duty-cycle rectangular wave, the effective value is found from the heating effect: over 2 s, the waveform is 2 V for 1 s and 0 V for 1 s, so the equivalent DC voltage satisfies (U^2/R)·2 s = (2^2/R)·1 s, giving U = 2/√2 = 1.41 V [#1880578] The integral form gives the same result: U_rms = sqrt((1/T)∫u^2 dt), and with duty cycle d = 0.5 this becomes U_rms = Umax·√d [#1885885][#17245805] The 1 V result mentioned in the thread is the average value, not the RMS value [#1880130][#1880578]
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  • #1 1880103
    elektrokiler
    Level 18  
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    Question as above. Amplitude Um=2V, period T=2s, duty cycle 50%.
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  • #2 1880130
    Filip
    Level 23  
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    total from ) to T UM/T dt == 1V
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  • #3 1880144
    elektrokiler
    Level 18  
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    Are you sure? The RMS formula for any periodic waveform looks a little different.
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    #4 1880578
    Aleksander_01
    Level 43  
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    Hello
    Colleague Filip calculated well ... but the average value of the voltage.
    From the definition of the rms value, this voltage (a rectangle with a duty cycle of 50%) must give off the same amount of heat as a DC voltage in the same period (I messed up a bit, but I'll give you a picture below that will explain everything). So P=U*I, I=U/R that gives P=U^2/R, and the heat generated is energy, so we multiply the power by time, which in our case is 2 seconds. It was for direct current.

    Now we calculate for a rectangle with a filling of 50%, i.e. for one second we can assume the waveform as a constant voltage of 2 V.
    The thermal energy generated in both cases must be equal, so (U^2/R)*2seconds = (u^2/R)*1second (the second second is zero, so we don't take it into account). Now simple mathematical relations and we get the formula U=u/2^0.5, which means that the rms value of a square wave with a duty cycle of 50% and an amplitude of 2 V is 1.41 V.

    or

    U=((1/T)*integral from 0 to T zu^2 after dt)^0.5 (for more advanced).

    We associate the average value of the current with the amount of flowing charge, i.e. with the surface area in a given period.
    We associate the effective value with the heat generated in a given period.

    Goodbye (it's nice to go back to school)
    Attachments:
    • Calculating RMS Value of a 2V Amplitude, 2s Period, 50% Duty Cycle Square Wave wartość skuteczna.jpg (15.2 KB) You must be logged in to download this attachment.
  • #5 1881187
    octanq
    Level 12  
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    In my maths terms, the rms value is the average of the absolute value of the function** (I change all negative values to positive ones), i.e. in this case in the U[V]-t[s] axis system:

    from t=0 to t=1s: U is constant and equals 2V (U=Um=2V),
    from t=1s to t=2s: U=0, ***

    change all negative values to positive ones (remains unchanged)

    and now I calculate the average normally, so in this case the average will be 1V, because for the first second it was 2V, and for the second: 0V.

    ** this def. is equivalent to the formula given by Aleksander_01 (squared first, then square root - positive values remain);
    *** I'm not sure if this is how the waveform looks like, but I'm giving the principle (isn't it about alternating current?);
    -
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  • #6 1881333
    jony
    Electronics specialist
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    And I always thought that the RMS value of a symmetrical square wave with 50% duty cycle equals its amplitude, which is 2V
    Attachments:
    • RMS.doc (43 KB) You must be logged in to download this attachment.
  • #7 1881374
    Aleksander_01
    Level 43  
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    Hello
    Jony I read your previous posts and you seem like a sensible guy, and here is this post. You probably haven't thought about what you're writing, after all, it's not about a symmetrical waveform (then, yes, the rms value is equal to the max value, i.e. in our case 2 V). Look carefully at your attachment (last item - square wave).
    I'd like to believe that you just made a mistake, which happens to everyone.
    Your previous posts prove that you have proper knowledge (and here's a gaffe).
    Regards
  • #8 1881428
    jony
    Electronics specialist
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    Yes Aleksander_01 you are totally right my mistake :cry: sorry. The effective value is 1.41
  • #9 1885804
    elektrokiler
    Level 18  
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    I didn't express myself very clearly, but my friend Aleksander_01 understood what the mileage was (unsymmetrical). Before I wrote this post, I counted from the formula (integral over the period under the root), which was also given by my colleague Aleksander_01, but somehow I get a different result. Could you show what and how?
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    #10 1885885
    Aleksander_01
    Level 43  
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    I figured if it was symmetrical it wouldn't be a problem.
    You know the formula, then we substitute: for T we substitute 2 because the period lasts 2 seconds, we write the integral from zero to T / 2 (that is one second, we only care about this part of the waveform), then it is u^2 so for u we put 2 because the amplitude is 2 V. And we count. And it comes out 2^0.5.

    You can create the pattern yourself, you just need to know the principle that I described in the previous post. In your case, it will be: PT=pT, ((U^2)/R)T=((u^2)/R)T/2 and from this equation comes this integral.
    Regards
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  • #11 1890634
    elektrokiler
    Level 18  
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    Thanks a lot buddy Aleksander_01 . I'm not very good at math and this is where it showed itself...
  • #12 17245805
    ryszard1955
    Level 20  
    Posts: 257
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    In sum:

    Usk=Root(dT/T)*Umax where dT/T is the duty cycle, Umax is the amplitude

Topic summary

LABEL_AI_GENERATED
The discussion revolves around calculating the RMS (Root Mean Square) value of a square wave with a 2V amplitude, a 2-second period, and a 50% duty cycle. Various participants provide insights into the calculation methods. The RMS value for a square wave with a 50% duty cycle is derived from the relationship between the power dissipated in a resistive load and the effective voltage. The consensus is that the RMS value is approximately 1.41V, which is calculated using the formula U = Um / √2, where Um is the amplitude. Some participants initially confused the RMS value with the amplitude, leading to clarifications and corrections throughout the discussion.
AI summary based on the discussion. May contain errors.
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