Re: Average, RMS and Power Factor made easy!

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

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