Steve Nosko wrote:

The term "RMS POWER" while not technically correct for anything
practical is tossed about and I suspect it is 'meant' to mean true or
average power as generally understood by those schooled in the field.

It was somewhat in that sense that I was trying to use the term about 15
years ago. But I was shot down for a number of reasons... with all of
which, I now agree.

1. When used without any qualifier, "power" always means the value
averaged over one or more complete cycles, so it is redundant and
confusing to add "RMS" where in fact no qualifier is necessary. This is
the strongest technical reason for not using it.

2. I was using "RMS power" to mean exactly what Steve says: "average
power as generally understood by those schooled in the field", or "power
averaged by the correct use of the RMS method". However, that attempt to
condense a much bigger concept into two words just does not work.

It's even worse than a simple failure to communicate. The mere mention
of "RMS power" is guaranteed to hijack the whole discussion, and the
point you actually wanted to make will be lost forever.

3. Any term that is used in the "hi-fi" industry - even by the so-called
"good guys" - is automatically tainted.

In the end, I decided that using "RMS power" was causing *many* more bad
effects than good... and after 15 years, I'm still being punished for it
:-)

Those are the reasons why I now come down firmly on the side of "just
call it power".


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Tue, 05 Oct 2004 08:53:31 -0700, Bill Turner
wrote:

On Mon, 04 Oct 2004 17:45:56 GMT, Gary Schafer
wrote:

Consider 1 volt peak x .707 = .707 volts rms. .707 volts x .707 volts
= .5. Divide that by 1 ohm and you have 1/2 watt.

Ok so far.


Using rms factors, convert the rms values to peak. .707 volts x 1.414
= 1 volt peak. OK.

OK so far.


Now try and find peak power like you would find peak voltage from a
known rms value.
Do that with the power value that you want to call rms power and you
have .5 x 1.414 = .707 watts. Not the 1 watt peak you were looking
for.

You used the wrong factor. To convert RMS power to peak power (sine
wave only) the factor is 2, not 1.414. The peak power in your example
is actually one watt, just as expected.


Your answer is what my point is all about. 2 is not an rms factor.
Nowhere do you use 2 to find an rms value. But 2 is used when
associated with average values.

As Steve said in another post, power is often referred to as rms power
as it is derived from rms voltage. But it is important to realize that
there is a difference even though it may not be stated.

If it were really rms power then you should be able to find peak power
by multiplying by 1.414 as you do with rms voltage. But that doesn't
work because power is not an rms value.

73
Gary K4FMX

People who use the term "rms power" are braggarts, attempting to show-off
how psuedo scientifically and engineering-ly educated, politically-correct,
and clever they are.

Whereas all they accomplish is to display to the mostly sensible world their
abysmal ignorance.

Articles in Audio Hi-Fi magazines fall below even lower standards of silly
journalism. There ought to be a law against it !

There's only one sort of "power" and that is simply "power". I have serious
doubts about such vague and indeterminate notions as "reflected" power.

In all my experience I have never found any use for such terms.
----
Reg.

In article , "Reg Edwards"
writes:

People who use the term "rms power" are braggarts, attempting to show-off
how psuedo scientifically and engineering-ly educated, politically-correct,
and clever they are.

Whereas all they accomplish is to display to the mostly sensible world their
abysmal ignorance.

Articles in Audio Hi-Fi magazines fall below even lower standards of silly
journalism. There ought to be a law against it !


While it's a misnomer, there's a reason the audio folks use the term "RMS
power".

Back when stereo was hi-fi, amplifiers were simply rated in watts output. The
test method was simple: you fed a sine-wave audio tone into the amp and
measured the continuous output power into a matched resistor load. A "50 watt"
amplifer could deliver 50 watts of audio power continuously.

Then a bunch of things happened.....

First off, there was stereo. Audio amplifiers became 2 channel, usually with a
common power supply. Manufacturers found they could get more power if only one
channel was operating - particularly if the power supply was skimpy to begin
with. So they tested that way, and doubled the result.

Then came solid state. Some early designs could deliver amazing levels of power
into very low impedance loads - for a short time, anyway. So the idea was born
to test the amps by feeding a pulsed signal rather than a continuous tone, and
using a very low impedance dummy load.Plus one channel at a time. Plus
measuring peak power, not average power. With big capacitors in the power
supply, and all the tricks optimized, some amazing power levels could be
measured.

Of course you'd never realize such power in actual operation, but the
manufacturers rationalized that music wasn't sine waves anyway.

End result was that an amp which would have been rated as maybe a "20 watt
stereo amplifier" under the old scheme (two 20 watt channels operating
simultaneously) could be rated as high as "200 watts IHF music power" or some
such. All sorts of terms were invented, mostly to favor a particular test
method.

The serious audio folks coined the term "rms power" to mean the old way of
actually feeding a continous tone to all channels and measuring the continuous
audio power developed.

73 de Jim, N2EY

Then came solid state. Some early designs could deliver amazing levels of
power
into very low impedance loads - for a short time, anyway. So the idea was
born
to test the amps by feeding a pulsed signal rather than a continuous tone,
and
using a very low impedance dummy load.Plus one channel at a time. Plus
measuring peak power, not average power. With big capacitors in the power
supply, and all the tricks optimized, some amazing power levels could be
measured.

Of course you'd never realize such power in actual operation, but the
manufacturers rationalized that music wasn't sine waves anyway.

End result was that an amp which would have been rated as maybe a "20 watt
stereo amplifier" under the old scheme (two 20 watt channels operating
simultaneously) could be rated as high as "200 watts IHF music power" or
some
such. All sorts of terms were invented, mostly to favor a particular test
method.

That is similar to how computer speakers can get 50 to 100 watts rating out
of a wall cube and a look inside will see the speakers rated around 2 watts.

Ralph Mowery wrote:

[snip discussion of "IHF power" and other specious ratings]

That is similar to how computer speakers can get 50 to 100 watts rating out
of a wall cube and a look inside will see the speakers rated around 2 watts.

I have frequently had a good laugh at 50 to 100 watt computer speakers
fed by a single 12 VDC 750 mA wall-wart, not to mention stereo amps
with ratings plates showing 120 VAC 300 mA for an amp supposedly rated
at 100 W per channel. WHat color is the sky in _their_ universe?

--
I think anything that comes from M$ can safely be called a "coprogram".
Once it's fossilized, it's just a coprolite.
-- me, in the Monastery

On Wed, 06 Oct 2004 08:24:08 -0700, Bill Turner
wrote:

On Tue, 05 Oct 2004 17:13:54 GMT, Gary Schafer
wrote:

If it were really rms power then you should be able to find peak power
by multiplying by 1.414 as you do with rms voltage. But that doesn't
work because power is not an rms value.

_________________________________________________ ________

Here's where you are going wrong. You are only multiplying the VOLTAGE
by 1.414 and forgetting to multiply the CURRENT by 1.414. Look at the
entire formula:

P(pk) = VRMS x 1.414 x IRMS x 1.414

You can multiply the two 1.414 factors together and get - voila - 2.

So the formula becomes

P(pk) = VRMS x IRMX x 2.

And that's where the 2 comes from. What you were doing is multiplying
the peak voltage by the RMS current, which is incorrect.

Make sense?


oooooow. I think I will give up here. I made too many posts on this.

Once it becomes power it is no longer an rms value.

73
Gary K4FMX

On Wed, 06 Oct 2004 10:22:52 -0700, Bill Turner
wrote:

On Wed, 06 Oct 2004 16:17:56 GMT, Gary Schafer
wrote:

Once it becomes power it is no longer an rms value.

_________________________________________________ ________

To be unambiguous, the word "power" needs to have an adjective attached,
like "DC power", "RMS power", "Peak power", "Real power", etc, etc.

Lots of times, people get lazy and say only "power", but that leaves it
open to mis-interpretation. I'm guilty of it too.

How about "average power" the correct term.

73
Gary K4FMX

1- The term "RMS power" has no mathematical or electronically correct
meaning. It is technically meaningless. On the other hand, we often use
terms to "imply" things within a certain circle. This is very common and
accepted by many.

RAM is random access memory, but so is ROM (random access, that is) We all
know what is meant.

Though Gary used the term "RMS Power" in his math description, It is a
strange usage. Perhaps the "audio folks" coined it for some reason, but it
is not a technical term in circuits, electrical Engineering or what ever you
want to call serious electronics fields. HOWEVER, he did the correct math
and he did enough explaining that it was clear what he meant by it. I
maintain it is the meaning that is important and it is important to look
past the differences in tech-speak some may have. Discuss the concept --
work to arrive at the meaning and don't quibble over terminology if at all
possible. Too many time is see flames which jump between concept and
terminology choice. Pick a common term and move on.

Not to long ago, it was common to call average power "true power". If
circuit conditions are kept as they are for long enough, this is the power
which goes wherever. I'll leave the philosophical (sp) discussion of just
what power this is to Reg.

B- There is "Peak Power". Typically, this is the power at the peak of the
waveform (often sinewave, but not necessarily). This power DOES occur at
that time. The peak power is there. Voltage is there and current is there
at the same time and power happens. For "Peak-to-peak" it ain't so.

There is never any peak-to-peak voltage which is present at an instant
causing a peak-to-peak current to flow at that instant resulting in a
peak-to-peak power.

B2 - We usually talk about the power over one cycle because that is enough
time to know what it really is over the long term (assuming the wave sticks
around for the long term)...

3- I disagree. An adjective or modifier isn't "needed" but it sure can help
if there may be confusion as to just what the subject is.

D- What Gary said is true. "Once it becomes power it is no longer an rms
value". This is because RMS values of voltage and current are simply tools
we use to arrive at the true, average power...call it what you like We have
to because there ain't no gizmo which measures the power directly (I'll
ignore all the discussion about thermal means [or whatever] actually
measuring the power).

5- What Gary said is false - "If it were really rms power then you should be
able to find peak power by multiplying by 1.414 as you do with rms voltage.
But that doesn't
work because power is not an rms value."
--- NOPE ---
RMS has a specific meaning (in this context) and it ain't in regard to
power. It is applied to the voltage and / or current when that is what you
want to use to find power. The part about "multiplying by 1.414" can not be
applied to power. This is an invalid extension of the math behind RMS...not
applicable...apples and oranges. Applying the wrong formula to the right
(or wrong) situation.


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


"Bill Turner" wrote in message
...
On Tue, 5 Oct 2004 19:03:48 +0000 (UTC), "Reg Edwards"
wrote:

There's only one sort of "power" and that is simply "power". I have
serious
doubts about such vague and indeterminate notions as "reflected" power.

__________________________________________________ _______

Is that so? Then what do you call the instantaneous power which occurs
at the top of a cycle of AC. I call it "peak".

--
Bill W6WRT

How about:
average power =

where V and I are understood to be the effective or rms values of the
voltage and current.

http://hyperphysics.phy-astr.gsu.edu...c/powerac.html
--

"Bill Turner" wrote in message
...
On Wed, 06 Oct 2004 18:15:11 GMT, Gary Schafer
wrote:

How about "average power" the correct term.

__________________________________________________ _______

This will be the third time I've asked for an official source for this
"correct" term. If there is no reply, I shan't be asking again.

--
Bill W6WRT