:      Hello, 
: 
:    Let me introduce a problem:
: 
:    When I measure a sinusoidal wave (voltage) with a digital voltmeter, using 
: AC mode, my output is an rms value (a peak value over 2 squared). / Right? / 
:    When I measure a square wave in the same mode (AC), my output is equal 
: to a peak value, actually, to the upper flat boundary of the wave.
:    I assumed, that a digital voltmeter makes some kind of integration of the 
: input value, and divides it over the wave period. / Right?/
:    Now, I used it to measure the same  square wave as above, but distorted 
: by high-frequency harmonics. Ideally, output should be the same, but...
: The output value was only about 10% of the previous one! 
:    Why? What is the nature of this output value? What does the voltmeter 
: actually measure? And what does it show?  


Re: RMS readings

Unless the DVM *says* it's measuring RMS, it's probably Average voltage.
The input is diode rectified and measured as DC.  If it says it's RMS
and but measures square/triangle/etc.  incorrectly, it's measuring
average and multipling by a correction that's *only* true for sine waves
(i.e.  Vave*(0.707/0.63) = Vrms).  If you want correct RMS for (most)
any waveform, you need a "True-RMS" DVM/DMM which literally does the
Root-Mean-Square calculation in either analog or digital circuitry.

: 
:    Related question (less important to me):
:    What are advantages and disadvantages of digital voltmeters to compare with 
: analog ones? 

The last significant advantage of analog (IMO) ** was ** being able to
"see" the signal if it was changing over time (e.g.  checking
electrolytic capacitors).

Anymore, most DMM have bargraphs, etc. that duplicate this.

: 
:    Thank you for your attention, you could mail me your opinion at
: avm1993@zeus.tamu.edu or open a discussion here. I would appreciate either 
: way.
: 
: 
: Alexander V. Mamishev
: 
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