# Oscilloscope and DMM: Vrms and Veff

Discussion in 'Homework Help' started by ellulclaire, Nov 19, 2009.

1. ### ellulclaire Thread Starter New Member

Nov 19, 2009
1
0
e) Adjust the amplitude control of the function generator until the signal has a 6V peak-to-peak swing. The resultant form will have the following mathematical equation:
v = Vm sin2(pi)ft = 3sin2(pi)500t

f) The sinusoidal signal 3sin2(pi)500t has an effective value determined by:
Veff = 0.707(3V) = 2.121V
Connect the DMM directly across the function generator in the ac rms mode and adjust the oscilloscope output until Veff = 2.121V. Then connect the output of the function generator directly to the scope and note the total peak-to-peak. Is the waveform the same as that obtained in part (e)? Explain.

Can someone pls tell me whether they should be the same or dfferent? Thanks!

2. ### Papabravo Expert

Feb 24, 2006
11,939
2,559
From the description you have provided it looks like they should be the same. The motivation for the computation is to correctly gage the power in an AC circuit when an RMS voltage is multiplied by an RMS current.

Notice what would happen if you used average voltage and average current.

3. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,349
731
If you have a True RMS multimeter, then the values should be the same.

If you have a lower end multimeter, the value could be off by a bit.