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Re: AVERAGE Power/Phase angle confusion



Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <free0076-at-flinders.edu.au>



On Tue, 9 Jan 2001, Tesla list wrote:

> Original poster: "harvey norris by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <harvich-at-yahoo-dot-com>
> 
> 
> I am picking this thread apart only one or two piece
> by refutation: necessary for this group to resemble a
> resemblance of electrical knowledge!
> --- Tesla list <tesla-at-pupman-dot-com> wrote:
> > Original poster: "by way of Terry Fritz
> > <twftesla-at-uswest-dot-net>" <free0076-at-flinders.edu.au>
> > 
> > 
> > 
> > On Mon, 8 Jan 2001, Tesla list wrote:
> > 
> > > Original poster: "harvey norris by way of Terry
> > Fritz
> > <twftesla-at-uswest-dot-net>" <harvich-at-yahoo-dot-com>
> > > 
> > > 
> > > --- Tesla list <tesla-at-pupman-dot-com> wrote:
> > > > Original poster: "Gary Johnson by way of Terry
> > Fritz
> > > > <twftesla-at-uswest-dot-net>" <gjohnson-at-ksu.edu>
> > > > 
> > > > Sorry to pick nits, but a recent reference to
> > RMS
> > > > power set me off, rather
> > > > like fingernails on a slate blackboard.  Our
> > meters
> > > > measure measure average
> > > > voltage and current on the dc ranges, rms
> > voltage
> > > > and current on the ac
> > > > ranges, but only AVERAGE power (never RMS
> > power).
> > > Are not these the same thing? If we integrate the
> > > Power equation curve for a half cycle is not the
> > area
> > > under this curve the sime area as if the rms
> > voltage
> > > and rms amperages were multiplied?
> > 
> > Not if they are out of phase.
> BS or horse manure,or textbook misinterpretation
> whichever variety you prefer. Let me ask the ENTIRE

You don't understand what you are talking about.

> TESLA LIST a simple question. I have a .45 Henry Coil
> system of 38 ohms, and a 56 Henry coil of 1000 ohms.
> Which system is more reactive than the other,or which
> is more "out of phase"  by the cherished mathematical
> standards whereby the myth of differing phase angles

Differing phase angles is no myth - ask someone who knows
how to use a CRO to set up a system of viewing the voltage across an
inductor and the current through it. And the 56 henry coil is more
reactive, it has a reactance of 21.1 kilohms at 60 Hz. The resistance
values aren't used in determining reactance.

> is established? The experts know the answer to this
> simple question in which the answer is so obvious it
> deserves no mention! The 1000 ohms I measure from a 56
> Henry coil at wall voltage AC consumes 5 ma from the
> wall AC 120 volt input, that is the recorded amperage
> by the meter, rms reading or what/not in the reactive 

I agree, if you add 1000 ohms resistance to 21.1k inductive, you end up
with approximately 21.1k ohms at a phase angle of 87 degrees inductive. I
trust that you won't argue with that (ooer, there's a phase angle!!). Then
the current drawn from the wall is just 120/21.1k = 5.69 mA at a phase
angle of 87 degrees lagging the voltage across the inductor (the mains
supply).

> amperage reading state. In its condition of drawing a
> reactive current 90 degrees out of phase with the 120
> volts input across that 1000 ohms, only a possible 120
> ma would occur if the coil was in perfect resonance,

How would you end up with a resonance with the mains??

> but in this reactive current measurement instance the
> 5 ma is shown by the meter as the resultant amperage
> experienced by the meter showing the amount of current
> present in that impedance; once again THAT is  the
> amount of current conduction ALREADY predicted by what
> the mathematical phase angle trigonometric
> calculations will deliver and the meter is only
> verifying that result and not lying to you!!!!  

But I'm not disagreeing with the meter reading, it's what is expected. The
problem is that you insist on neglecting the power factor when calculating
power, not in the operation of meters. We both agree that ammeters
measure the actual current flowing and nothing else.

> That is what is ALREADY predicted to be the
> amperage consumption which is exactly what the meter
> reads by the appropriate phase angle considerations. I
> assumed that was enough to end the thread, but maybe
> not...
> 

I thought it was ended, but you're still not convinced.

> 
>  And the area needs to
> > be taken over a full
> > period and divided by the period to take into
> > account harmonic distortion 
> > and find the average. The average power is called,
> > funnily enough, average
> > power. Definitely NOT RMS power, that would be
> > something entirely
> > different.
> I give up?
> > > > Average power is the
> > > > product of rms voltage, rms current, and power
> > > > factor. 
> > 
> > > I definitely disagree here. If you are making AC
> > > MEASUREMENTS on any circuit, those measurements
> > > themselves are already the result of the phase
> > angle
> > > conditions. If I am measuring a fairly resonant
> > 
> > Definitely not, two-wire devices like multimeters
> > can't measure the phase
> > difference between two signals now can they?
> Yes they can without falling into the trap of this
> argument..., there was never two signals to begin
> with, only the figment of mathematical imagination
> that calls the OHMS laws conduction value the "in
> phase" signal. This non argument is based on
> inadequate mathematical knowledge.  

Please don't insult me. This is what we are arguing about:

Somebody said that P = V I  where P is average, V is RMS and I is RMS

I ended up saying that this is only true for a resistive load. You must
also multiply by cos(theta) and this fixes it for non-resistive loads.

If you like what I just said, then we are in agreement. I think we may be
arguing about different things we think the other person has said. If you
do find a problem with the above statement, then we have a problem, since
the paragraph above this one is 100% correct.

> The amount of amperage consumed by the
> meter itself does not give a linear indication of the
> predicted phase angle but that again is the job of
> trigonometry to ascertain the phase angle. The PHASE
> ANGLE is the deduction MADE AFTER THE METER READING,
> NOT BEFORE! The inverse interpretation that many hold

The phase angle may be deduced from the meter reading, and the phase angle
results in the meter reading. It is because the voltage and current are
not in phase. The phase angle is not a myth, it is not some formula
someone came up with, you can witness it in all its reality on a CRO. Try
it. Please don't insult me or the mathematicians who make life easier for
all of us although many people don't know it.

> in common is wrong. Sorry for the cherished beleifs
> held in your knowledge box, but you should have never
> read something into the mathematics that was never
> there in the first place. No need for further comment

Like I said grab a CRO, it's there. Better yet, learn some differential
calculus and then read a first year university circuit theory book. You
won't even need a CRO then, you'll believe it anyway.

> on this thread.... 
> Sincere in common Sense  HDN

Does that mean that engineers lack common sense? Or that they don't know
what they are doing?



I tried. Really, I tried. Others can see that I tried. Now I'm tired and
I'm going home. Being stuck in a robotics lab for this long writing emails
isn't productive and just makes me more tired.


Darren Freeman