Hi there,A voltage composed of a DC voltage and two sinusoidal with different frequencies:
u(t)= -3+3sin(100πt)-4sin(400πt)
What will a True-RMS-voltmeter show, if set to "DC" and "AC"?
I suppose in DC it will show -3, am I right?
How do I calculate the AC?
U_rms=sqrt((-3)^2+(3^2)/2+(-4^2)/2) = 4.6368Hi there,
You do not need to calculate each part individually, you can do it all at once.
RMS is defined as the root of the mean of the square of the signal.
Thus you would first square the entire signal, then find the mean, then take the square root, that gives you a result which should always be positive. For a complex signal you often have to solve for the integration times first. Do you know how to do all this?
A hint is the RMS value lies between 4 and 5 volts RMS.
When i insert the value I calculated in sqrt(DC^2+AC^2), I do get 4.6368 so it seems like I got the right answer. But im still not sure if set to DC, will it show -3 or 3?Hi,
WOW, a resounding *YES*, very good work there for the 4.6 result.
That was the second way to do it.
But why did you divide by 2 in the second part?
Note that you must get the same result (4.6) if you do:
sqrt(DC^2+AC^2)
When i insert the value I calculated in sqrt(DC^2+AC^2), I do get 4.6368 so it seems like I got the right answer. But im still not sure if set to DC, will it show -3 or 3?
by Aaron Carman