🚀 go-pugleaf

On 9 Aug 1995, Walter Gray wrote:

> In article <408rk1$6gh@sol.ccs.deakin.edu.au>, andrew@deakin.edu.au (Andrew Cerasuolo) writes:
> >Hi to all,
> >Can anyone help me with calculating the average or true rms (Root Mean Square)
> > value of a pwm signal.
> >i.e.
> >	______         _____	   ___
> >	|    |	       |   |        ^
> >	|    |	       |   |        C	
> >________|    |_________|   |_____  ___
> >	
> >	|<A >|<-- B--->|<A>|     
> >
> >where A & B are times, f = 1/(A+B)  .
> >C is a voltage from 0 to whatever volts.
> >I know that as the frequency of the signal increases the average/rms is 
> >increases but is there a mathematical formula for this relationship ?.
> >Any answers would be appreciated, Ciao Andrew.
> >--
> >Andrew Cerasuolo                 The above comments are mine solely and
> >Biol. & Chem. Sciences Workshop, not that of Deakin University.
> >Deakin University, Geelong,     
> >Vic 3217, Australia              andrew@deakin.edu.au
> 
> 
> mean = C*A/(A+B)
> rms = C*sqr(A*B)/(A+B)
> 
> To those who got the wrong answer, remember that rms is the root
> mean of squares ABOUT THE MEAN!

Huh? I agree with the mean value you get, but how does that rms relate
to the mean? I squared the function, integrated from 0 to A, multiplied
by 1/(A+B), and took the square root of the whole thing to get:

	rms = c*sqr(A/(A+B))

Maybe I've hosed the arithmetic or something, but I can't see my error.
Or maybe I just don't know what you mean by "ABOUT THE MEAN". (The
method I'm using here produces the correct result for sinusoids).

--
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Steve White, Lab Technician @ Human Interface Technology Lab
e-mail: stevew@hitl.washington.edu       voice: 206.616.1411
http://www.hitl.washington.edu/  (My page under consruction)
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