"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

On Tue, 24 Feb 2004 18:28:57 -0600, "Steve Nosko"
wrote:
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.

And then you offer in contradiction:

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

Such is reality. There is no such thing as symmetry, except on the
academic page. However, I am not so pedantic as to suggest that
shortcuts don't abound; simply pedantic enough to point out you don't
make claims to accuracy (admittedly none were offered that I was
responding to) through fudge factors when so many alternatives remove
doubt.

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.

Of course, but it is eminently doubtful if you can actually express it
mathematically. Far more here own o'scopes than works of multiple
regression. Graphical analysis is first year engineering stuff out of
drafting class.

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)

Hi Steve,

Yikes? Look at your own response to shudder. ;-)

You offer the doubt and then correct your error in the space of three
sentences. From that I must suppose it was a rhetorical question, but
the "yikes" heading it promises more clarity in response to what you
apparently complain of. After all, a complex, compound sentence with
ellipses and nested parenthetical statements? You lose points for
unpaired braces and lack of punctuation throughout and at the end.

Do the power meters on the outside of our houses take all those
factors into consideration and REALLY show TRUE watt hours?
For at least a Century now.

The power companies offer as close to pure symmetry as you could buy.
They also offer long term time accuracy to far better than any source
short of WWVL.

73's
Richard Clark, KB7QHC

OOPS!

"Richard Clark" wrote in message
...
On Tue, 24 Feb 2004 18:28:57 -0600, "Steve Nosko"
wrote:
I assumed Richard's intent here is that you only have to do the
calculation for one full period ...symmetrical, then only one half
period...

And then you offer in contradiction:

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

This was a stupid thing to add at this point since it addresses
something which I did not explain, so I'm sure it looks weird. I didn't
even say what was in my mind. Namely, that with the DC + AC you still need
to do one full period of the periodic part.

What I was poorly referring to was this:
If you can break down the signal into component parts such as:
DC
Periodic part #1
Periodic part #2
etc
Then there is a formula for the total RMS which is the square root of
the sum of the squares. It is in one of the papers I linked previously.
That is one way to do an AC+DC situation. Second formula in the Intl Rect
paper:
http://www.irf.com/technical-info/an949/append.htm


[...] There is no such thing as symmetry, except on the
academic page. [...] you don't
make claims to accuracy (admittedly none were offered that I was
responding to) through fudge factors when so many alternatives remove
doubt.

I think is it safe to say that we each determine our own tolerance for
error. Five percent for power is ok for my purposes. SO approximating
waveform functins is just fine.


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.

Here, I'll take issue. I believe that the basis for the many
"correction factors" for RMS of various shapes is indeed the mathematical
integration of a function rather than the "Simple concept" of a graphical
solution (if that is what you meant). There is a mathematical integral of a
sine wave.

I think you'd be hard pressed to prove that the average of a sine wave is
2/pi exactly using graph paper. You could certainly say it sure looks close
to 2/pi, but is it exactly pi?... can't say for sure.

Case in point is the phase controlled sine wave made by SCR light
dimmers. I find it hard to believe you can graphicaly come up with the
formula:

Sqr-root[ D/2 + sin[pi(1-D)] cos[pi(1-D)]/2pi

I must also add that the graphical solution and mathematical integration
are different implementations of the same concept. I don't intend to say
that one is wrong and one is right.

Now, for Richard, C. Is the thing coming out of the AC outlet an exact
sine wave...no. It is very noticably flattened on the top by all the power
supplies drawing peak currents near the peak. There must be other
corruptins as well. However, if I assume it is a sine wave, will my
calculations come out very close, I believe Yes.

Now in all fairness, I won't dispute that you can use the graphical
method to find the RMS to any desired accuracy, just not exact...without
being able to integrate the waveform.


Of course, but it is eminently doubtful if you can actually express it
mathematically. Far more here own o'scopes than works of multiple
regression.

Graphical analysis is first year engineering stuff out of
drafting class.

Integration is first year engineering stuff out of calc class. At least
it was for me. I am still amazed that I remember doing tripple integrals
then, and thinking...Gee, this ani't so hard after all!. Couldn't do one to
save my life now.


[...] you simply measure the caloric result and ignore
shape altogether.

I always thought that the common method of measuring RF power was pretty
cool! The Thermistor or bolometer. Here you balance a bridge with DC or
low freq AC. It heats the thermistor to the correct resistance. Then, when
you add RF power, the thing heats up more and changes resistance. So, you
remove some DC power to get back to the correct resistance and that amount
is easy to figure. That is how much RF you put in. Cool. I think it is
correct to say that you absolutely cannot measure power *directly*. You
must measure something else which is affected/caused by the power...comment?


[..] migrated from Power to some other consideration

Not trying to migrate. I just think its a cool method.



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, like me, Richard Clark makes a really long answer that says...Yes.

Got me!
I have NO idea how the watt-hour meter works...and don't want to try
to understand at this point.

73,
--
Steve N, K,9;d, c. i My email has no u's.

Steve Nosko wrote:
"I assumed Richard`s intent here is that you only have to do the
calculation for one full period...symmetrical, then only half
period..."

Maybe an advantage of graphical representation is manifestation of the
absurd. If the wave is not symmetrical around the zero volt axis, or if
one alternation has greater squared values, it may be apparent. You may
be able to see this in the mathematical expression for the waveform too.

The effective value of both alternations must be equal for the
determination of the value of only one alternation to suffice.

Steve also wrote:
"There ia a formula for the total rms which is the square root of the
sum of the squares.""

Sounds familiar. Sounds like Pythagoras.

Best regards, Richard Harrison, KB5WZI

On Wed, 25 Feb 2004 12:22:32 -0600, "Steve Nosko"
wrote:

[...] you simply measure the caloric result and ignore
shape altogether.

I always thought that the common method of measuring RF power was pretty
cool! The Thermistor or bolometer. Here you balance a bridge with DC or
low freq AC. It heats the thermistor to the correct resistance. Then, when
you add RF power, the thing heats up more and changes resistance. So, you
remove some DC power to get back to the correct resistance and that amount
is easy to figure. That is how much RF you put in. Cool. I think it is
correct to say that you absolutely cannot measure power *directly*. You
must measure something else which is affected/caused by the power...comment?


Hi Steve,

There are many classes of caloric devices, two of which you identify
that are common within the Metrologist's art, and wholly absent from
amateur activities. So here I must make a slight correction of your
description. Power meters contain two (2) such devices which form the
balanced halves of a bridge. One side is exposed to the RF, the other
side is exposed to the simpler DC or AC power that is known to a high
degree of accuracy. What you describe is the detector implementation
of the same devices (which exhibit non-linearity to perform
detection). They would, in the fashion you describe, offer good
"relative" power indication, but not absolute power (except through
substitution methods). As such, they are fairly common in precision
VSWR instrumentation especially when they are driven by 1KHz modulated
power sources, and in turn drive special AC VTVM's scaled to present
dB and VSWR to very high resolution.

A list of the methods:
The Crystal: 1N21/23/25/26...
The Bolometer (low power caloric)
The Barretter (a Bolometer): Sperry 821, PRD 630A
The Wollaston wire (a Barretter): actually a 0.01A glass fuse
The Carbon filament (a Barretter)
The Thermistor (a Bolometer): Western Electric 28A
The Thermocouple
The Thermopile (lotsa Thermocouples)

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 25 Feb 2004 12:22:32 -0600, "Steve Nosko"
wrote:

[...] you simply measure the caloric result and ignore
shape altogether.

I always thought that the common method of measuring RF power was
pretty
cool! The Thermistor or bolometer. Here you balance a bridge with DC or
low freq AC. It heats the thermistor to the correct resistance. Then,

Yea... Then I give only a partial description since trying to give
it completely would take pages, I decided to "overview" it.

However...


... and wholly absent from
amateur activities.

OOPS! "wholly"?? I've got one. A really nice (but un temp
compensated) thermistor mount) (but don't tell anyone that I have nothing
to drive it with -- the rest of the bridge.)

So here I must make a slight correction of your
description. Power meters contain two (2) such devices which form the
balanced halves of a bridge.

I gotta go back & look, (this was from the 60's) but there are two and
they are in series for the low freq and parallel for the RF. On the low
freq side it is a 200ohm mount. Now I hafta' remember how the RF was
handled .... musta' been to only one...let me think about this...


One side is exposed to the RF, the other
side is exposed to the simpler DC or AC power that is known to a high
degree of accuracy. What you describe is the detector implementation
of the same devices (which exhibit non-linearity to perform
detection). They would, in the fashion you describe, offer good
"relative" power indication, but not absolute power (except through
substitution methods).

OOPS again! You DO get absolute because you know how much low freq
power you remove. Isn't that the principle of the HP437 & 438's? or are
they doing something else...diode ... er...uh crystal if you're across the p
ond? I always thought they were, caloric, as you say.

--
Steve N, K,9;d, c. i My email has no u's.


As such, they are fairly common in precision
VSWR instrumentation especially when they are driven by 1KHz modulated
power sources, and in turn drive special AC VTVM's scaled to present
dB and VSWR to very high resolution.

A list of the methods:
The Crystal: 1N21/23/25/26...
The Bolometer (low power caloric)
The Barretter (a Bolometer): Sperry 821, PRD 630A
The Wollaston wire (a Barretter): actually a 0.01A glass fuse
The Carbon filament (a Barretter)
The Thermistor (a Bolometer): Western Electric 28A
The Thermocouple
The Thermopile (lotsa Thermocouples)

73's
Richard Clark, KB7QHC

On Thu, 26 Feb 2004 15:20:06 -0600, "Steve Nosko"
wrote:
OOPS again! You DO get absolute because you know how much low freq
power you remove. Isn't that the principle of the HP437 & 438's? or are
they doing something else...diode ... er...uh crystal if you're across the p
ond? I always thought they were, caloric, as you say.

Hi Steve,

They are Bolos (caloric) using PRD type elements. From your
description (barring the equipment name), it sounded like the typical
detector application. I can see you originally described a self
balancing bridge:

The HP bridge is powered three ways. It has a DC source to offer
temperature compensation and range changes (zero setting). It has an
AC Oscillator (~10 KHz) source in quadrature (topographically
orthogonal, across the bridge instead of over it). Basically, the
bridge temperature components (the Bolometer) act as an oscillator
level stabilizing feedback loop (much like the famous HP 200 which
used a lamp's negative resistance). The third power input is the
unknown RF which unbalances the heat causing the feedback to
re-regulate where the drive level changes (which is monitored by the
meter as the indication of the RF power applied).

The sum of the operation was that the bridge always operates at null
with the same heat burden for any applied RF power (within constraints
of course).

And yes, they are characterized as 200 Ohm mounts.

73's
Richard Clark, KB7QHC