Why does rectifier Vout measured with multimeter differ from scope measurements?

[king.oslo]

Hello there,

I hooked up the oscilloscope to my rectifier. The multimeter says input is 18.8V, which is correct according to the datasheet of the transformer. I connect the oscilloscope to the input of the rectifier, and it says it is ~56V peak to peak.

I then measure output from the rectifier using multimeter (16.5V) before hooking it up to the oscilloscope. The waveform looks correct, but it says the voltage is 27 peak to peak.

Why am I getting these readings on the scope?

 

[BrownOut]

Because the mulitmeter is measuring RMS, which is .7*v(peak). So, 27*.7=18.9, pretty close.

 

[king.oslo]

Ok, thanks! I will read about it on wikipedia, and learn about it! M

 

[Nigel Goodwin]

Because the mulitmeter is measuring RMS, which is .7*v(peak). So, 27*.7=18.9, pretty close.

Most meters don't measure RMS, they measure average, and scale it assuming a sinewave.

 

[BrownOut]

Doens't matter in this case. RMS is being reported.