"Richard Clark" wrote in message
...

The one I noted (mistake) was in your reference:
It is derived from the average of the squared current over a half cycle
which necessarily forces both a doubling, and a symmetry that is not
demanded of native RMS determinations. It then follows that the
commonplace illustration of the mains Sine wave completes the
illusion. Few EE students migrated beyond this simplicity because the
world is nasty place to measure power.

RMS by and of its mathematical nature through the squaring operation
negates any requirement for "half cycle" determinations (no issue of
negatives). It also preserves the natural order (of two forced by the
half). If you think about it, any biased sine wave impinging upon a
load imparts the power loss of the bias at the 180° portion of the
Sine cycle. RMS copes with this, the notion of half cycles does not.

I assumed Richard's intent here is that you only have to do the
calculation for one full period of the periodic component to derive the RMS
value - and if it is symmetrical, then only one half period will suffice.
This all assumes a symmetrical AC shape. .. I see no reason why this would
not be true.

However a DC biased periodic shape requires another squaring and root
operation if you capture all the components. It gets a bit more harry



The simple determination of RMS is the graphical integration of the
area under the curve. There are as many "correction factors" for RMS
as there are shapes, and they all derive from this simple concept.

Here I'll take issue with the ONE WORD "graphical". You can integrate
if you can describe the function of the wave shape mathematically.


When the computational horsepower requirement becomes enormous (there
are many here that give up too easily with complexity); it is the
provence of the "Old School" to suggest that since RMS is all based on
the notion of power, you simply measure the caloric result and ignore
shape altogether. This may be done with thermo-electric piles or
other measurable property transformers that perform the complexity of
integration through physics*. I can anticipate those who dearly
embrace the complexity that they shudder to face (such contradictions
of their love-hate relationships) when I hear Crest, or pulse/power
factor (or duty cycle) uttered. Clearly the problem will have
migrated from Power to some other consideration, but is dressed as an
RMS debate.

73's
Richard Clark, KB7QHC

Yikes! Not sure where you went on that last bit, Richard C...
Now, I ask. Do the power meters on the outside of our houses take all those
factors into consideration and REALLY show TRUE watt hours? I have one in
the basement and I think I figured out why I was seeing twice the reading I
should have (letting a light bulb sit on for awhile) ... I counted the
teeth to get the ratio of the gear train, just to find that it is printed
(somewhat cryptically) on the face) (I made a two wire / three wire
connection error)

73, Steve K9DCI