Understanding VAV, VRMS, & VDC Voltages

[asad1111]

i have read that vrms is the same as equivalent dc voltage but i have also read that vav and vdc are same but vav and vrms is not same vrms of sinosoid is zero but vav of sinousoid is not zero where i am wrong?

 

[vk6kro]

i have read that vrms is the same as equivalent dc voltage but i have also read that vav and vdc are same but vav and vrms is not same vrms of sinosoid is zero but vav of sinousoid is not zero where i am wrong?

You have most of that wrong.

You might like to read the Wikipedia article about this:
http://en.wikipedia.org/wiki/Root_mean_square

However, the average voltage of a sinewave (over a whole 360 degrees) is zero, but the power isn't zero because positive and negative voltages are equally effective at producing power, assuming a constant resistive load.
The average over a half wave is 0.637 times the peak value.

The RMS voltage of a sinewave is 1/_√2 times the peak voltage level or 0.707 times the peak voltage.

 

[Bob S]

V_rms = sqrt[V_meansquare(t)] =sqrt[∫V(t)²dt/∫dt] integrated over a complete cycle.

V_av = ∫V(t)dt/∫dt.

 

[jim hardy]

RMS mnemonic:
it's backwards.

instant by instant:
Square the instantaneous value
find Mean (average) of those squared values
square Root of that mean is RMS

and clearly that's a lot different from a simple average of the instantaneous values.
for one thing squaring them discards their signs.

but i think backwards so it's natural to me...