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Electronics => Beginners => Topic started by: Axtman on March 13, 2014, 03:48:04 am

Title: P to P measurements with an RMS meter?
Post by: Axtman on March 13, 2014, 03:48:04 am

How can I measure peak to peak voltage with an RMS multimeter? 

Title: Re: P to P measurements with an RMS meter?
Post by: w2aew on March 13, 2014, 12:14:48 pm

The answer is - you really can't.  IF the signal you are measuring is a sinewave that is within the frequency range of your RMS voltmeter, then you can calculate the peak to peak value by multiplying the RMS voltage by 2.828. 

Title: Re: P to P measurements with an RMS meter?
Post by: ConKbot on March 13, 2014, 12:15:51 pm

If its a sine wave youre measuring, mulitply by 2*sqrt(2), or 2.8284.  For RMS to Vpeak its RMS*sqrt(2) but since you want peak-peak, its 2x that.

If its not a sine wave, then make a voltage doubler,
(http://i.imgur.com/mLSXkV2.png)
(the transformer in the image is the AC source, substitute with whatever you want to measure) and add ~0.6 to 1V for the voltage dropped over the diodes. The drop would nominally be 1.4V for the 2 diodes, but with no load being drawn, then the Vf of the diodes will drop a lot.

Title: Re: P to P measurements with an RMS meter?
Post by: Wytnucls on March 13, 2014, 12:25:31 pm

Some true RMS multimeters have a 'Peak" feature, giving you peak to peak values.
Here is an example: (the 71B meter on the left was defective)

Title: Re: P to P measurements with an RMS meter?
Post by: ttp on March 14, 2014, 05:45:13 am

Nice to know, I got 71D.