root-mean square value for sinusoidal signal that superimposed onto the dc signal

Discussion in 'Homework Help' started by coolgirl, Dec 17, 2009.

  1. coolgirl

    Thread Starter New Member

    Dec 17, 2009
    hello....i have a problem in solving the questions related with the signal..Let, say a sinusoidal signal of magnitude A and period T is superimposed onto a dc signal of magnitude B to produce a resultant sine wave which have peak value as (B+A).The resultant wave start at B instead zero value..So,how to find root-mean-square value for the resultant wave???:confused:Please help me to solve this problem...:(
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    You just add the DC value to each point, and then work the RMS from there. :) You have to add it BEFORE the averaging, just can't tack it on at the end.

    From a practical standpoint, you can get rid of superimposed DC by using capacitor coupling (or transformer coupling) in many cases. Then it's just the RMS value.
  3. kdillinger

    Active Member

    Jul 26, 2009
    It is the square root of the sum of the squares. Square the DC term and add it to the square of the RMS term then take the square root of that total.

    RSS - Root sum square
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    The answer is


    I got this by squaring


    Discard the resulting purely AC terms (which average to zero), then take the square root of the remaining DC terms.
    I verified this with several example simulations in LTspice.
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    Which is the same as kdillinger's rendering .....

  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    It was a homework problem. I was explaining how to get there mathematically.