Re: Average, RMS and Power Factor made easy!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>

Terry
The 0.7071 factor for pk to rms value is ONLY VALID for sinusoidal periodic
waveforms.  Square waves are a different fish to fry...

I'll look in my Yokogawa references and see what the rms equations are for
a periodic square wave...  I believe the HP meter over the Tek any day of the
week in this case.

Regards

Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>
> Hi Darren,
>
> At 10:17 AM 1/19/2001 +1030, you wrote:
> >
> >
> >On Tue, 16 Jan 2001, Tesla list wrote:
> >
> >> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
> >>
> >> Hi Darren,
> >>
> >> I was using 0 to 1 volt 50% duty cycle square waves.  The 0.707 thing only
> >> applies to nice sine waves.
> >>
> >> Cheers,
> >>
> >>      Terry
> >>
> >
> >
> >Normally I'd say that too since many people abuse the 1/sqrt(2) factor for
> >non-sinewaves. However if you do the calculation on this square wave you
> >will indeed get the RMS value to be 0.707 V for 50% duty..
> >
> >Original wave:  0 V   50% of the time,  1 V 50% of the time
> >
> >Squared wave:   0 V^2 50% of the time,  1 V^2 50% of the time
> >
> >Mean of the squared wave: 0.5 V^2  (fairly obvious)
> >
> >I.e. mean squared value 0.5 V^2
> >
> >Therefore RMS value 0.707 V
> >
> >It's just luck that the 1 V peak sinewave has the same RMS value as a 0 V
> >-> 1 V  50% squarewave.
> >
> >
> >Have fun,
> >Darren Freeman
> >
>
> Gosh!  I hooked up the Tek Scope and the HP meter to measure the 0 to 5
> volt square wave calibration signal from the scope and got...  Two
> different answers!!
>
> The Tek scope gives 3.51 VRMS (suspiciously close to 0.7071 x 5) while the
> HP meter gives a value of 2.46775 VRMS (the meter loads the signal a bit)
> So the scope is following the "rules" to get 3.5355... while the HP is
> finding the equivalent voltage to generate the same power in a resistor
> 2.500...
>
> http://hot-streamer-dot-com/temp/RMS-Duh.jpg
>
> So just when I thought I had the RMS thing all figured out, I am all lost
> again :-p
>
> Cheers,
>
>         Terry