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Analog dynamic range, accuracy and number of bits

  • Thread starter Habib Bouaziz-Viallet
  • Start date
J

josephkk

Jan 1, 1970
0
Case? I'm telling you how people define and measure PF in the real
world. If you disagree on anything substantive, say so.

It is pretty simple John Larkin, You tried to say that PF is signed,
wikipedia, and its cited sources all disagree with that. The NEC (NFPA
70) disagrees with that, ANSI C2 (NESC) disagrees with that. You choose
what to say now.

?-)
 
J

josephkk

Jan 1, 1970
0
The ratio, actually. PF = real_power/apparent_power

where real power is in watts and apparent power is in volt-amps.

Not arguing with that, arguing over whether that is a signed quantity,
which cannot be from the definition.

?-)
 
J

josephkk

Jan 1, 1970
0
If you take simultaneous E and I samples at some sensible rate,

Auto-zero and then multiply the E and I samples. Lowpass filter to get
power, integrate to get energy.

Compute RMS current and voltage by squaring/filtering/rooting.

Multiply RMS current by RMS voltage to get VAs.

PF = power/VAs.

The only glitch here is that we lost the leading/lagging sign of the
PF. That can be fixed with some more signal processing.

But that is NOT part of the standard definition of power factor. See NFPA
70 (NEC), ANSI C2 (NESC), IEEE 100 for proper definitions. None of them
produce signed values.

?-)
 
J

josephkk

Jan 1, 1970
0
Interesting! Thanks, John. Sorry that was so basic. FWIW, I
defer to people who really know when power distro comes up - it's
not my field at all. I keep thinking it's mainly
impedance mismatch, when it's not really...

John Larkin is NOT someone to defer to in power distribution in anything
bigger than a VME box. Not that he wrong, but that he is NOT expert in
that field. I blow his doors off and i do not consider myself all that
expert in spite of having dealt with designs for 480 V, 2 MVA systems,
12.47 kV 50 MVA systems, and other things of similar size and many more
down to 120/240 V 50 A services, and down to PoE (about 50 VA max) and
SMPTE-170 video (1V P-P 75 ohms) and even smaller signals in the same
location. This a few feet apart, all of these, in the same location.

?-)
 
It is pretty simple John Larkin, You tried to say that PF is signed,
wikipedia, and its cited sources all disagree with that. The NEC (NFPA
70) disagrees with that, ANSI C2 (NESC) disagrees with that. You choose
what to say now.

Is COS(theta) signed?
 
J

John S

Jan 1, 1970
0
Oh my fucking god, you can't even get that correct...

Jamie

That would really worry me if I thought you knew what you were talking
about.

Start from first principles and develop the equations yourself to prove
I am wrong. Show your work.
 
J

John S

Jan 1, 1970
0
E gets confused with electric field--having a quantity and its line
integral called by the same symbol is, *ahem*, suboptimal.

Technical vocabulary is funny, especially in EE and other engineering
fields. Normally it's sort of folksy but very descriptive, e.g.
"soakage" or "walkoff". Sometimes it's quite irrational,
though--everybody says "voltage" for "potential", but if you say
"amperage" for "current", everybody laughs at you.

The Brits used to call it "electric tension". Do you UK folks really
say "the tension at this point is fifteen millivolts?"

Cheers

Phil Hobbs

Dr. H. Paul Shuch wrote that he avoids using the expression "voltage" to
differentiate between parameters and units of measure. He says that the
parameter EMF (electric potential) is measured in the unit volt.

Sounded good to me, so I once tried displaying "EMF = xxx volts" on an
LCD. They said no way. Show it as "Voltage = xxx volts".
 
F

Fred Bartoli

Jan 1, 1970
0
John Larkin a écrit :
How many electronic power meters have you designed, and how many have
you sold, to how many customers? I've done 10 or so, sold to about a
hundred utilities, universities, aerospace companies, apartment
owners. All but the latter cared about PF and, specifically, about its
sign.

Do you have any power meters? Do they report PF? Do they hide the
leading/lagging thing?

I don't know how power meters report, but...

1
Int 2.Veff.Ieff.Sin(2.pi.t).Sin(2.pi.t + phi).dt = Veff.Ieff.Cos(phi)
0

Nothing new there. According to the power/VA definition, indeed you can
have PF ranging from -1 to +1. No pb with that.

But now, for one value of PF (positive or negative) you have two
possible phase values, one positive and one negative and if you wanted
to unambiguously qualify the current vs voltage relation you'd need to
tell both signed PF and leading/lagging.
 
J

Jamie

Jan 1, 1970
0
Jim said:
Their customers are _required_ to do so. Larkin's just throwing his
usual sand in the air, trying to pretend expertise.

AFAIK the utilities can only correct for motor loads, and that
requirement is now, by statute, passed on to the customer, as well as
added charges for uncorrected loads.

...Jim Thompson
I don't know where you get your ideas from, but we are not required to
power correct our lines.

The only charge you receive is that of the extra energy that is used
if you don't power correct. And we do have 2 of them in use. THere is
no charge just for not using them.

Jamie
 
J

josephkk

Jan 1, 1970
0
If it's conveyed as speech or text, PF is usually expresed as
"leading" or "lagging." If it's in a 16-bit register, or an ascii
numeric string in a Telnet packet, the lead/lag is usually expressed
as a sign. But it matters, and the statement in Wiki that it's in the
range 0 to 1 isn't enough for a utility to know which way to kick in a
PF correction. You couldn't sell them a PF acquisition box that only
reports an unsigned value from 0 to 1.

The sign convention is that leading is negative.

So you are redefining it as signum(sin (theta)) * cos (theta).

?-)
 
J

Jamie

Jan 1, 1970
0
josephkk said:
John Larkin is NOT someone to defer to in power distribution in anything
bigger than a VME box. Not that he wrong, but that he is NOT expert in
that field. I blow his doors off and i do not consider myself all that
expert in spite of having dealt with designs for 480 V, 2 MVA systems,
12.47 kV 50 MVA systems, and other things of similar size and many more
down to 120/240 V 50 A services, and down to PoE (about 50 VA max) and
SMPTE-170 video (1V P-P 75 ohms) and even smaller signals in the same
location. This a few feet apart, all of these, in the same location.

?-)
That's a basic electrician knowledge base.

Jamie
 
J

josephkk

Jan 1, 1970
0
Then you have to hang "leading" or "lagging" somewhere off to the
side.

Works fine for me.
That's the same as a sign. Some people and systems literally use
the sign. My VME power modules don't hang an ASCII string off in 7
bytes of registers to spell out "leading" or "lagging"; we use a 2's
complement (signed fractional) integer.

That may be done, but it is not per the definition. Alternately you can
partition a bit-field and achieve the same goal more transparently. The
difference being lead/lag and magnitude will then not be 2's complement.

?-)
 
J

josephkk

Jan 1, 1970
0
Explain what "leading" and "lagging" mean, and why they don't matter
to you.

They have their usual meanings in my book. They are NOT part of the
definition of PF.

@Bob K7IQ a negative value for PF would physically mean that real power is
flowing in the direction opposite to expected. This happens when a motor
has a change in load or supply such that the power angle crosses 0 degrees
form normal operation. It does happen in real power distribution systems,
it is a necessary part of fault current calculations for protective
relaying. There are ANSI C37.2 relay functions that specific for this
situation.

?-)
 
J

josephkk

Jan 1, 1970
0
John Larkin a écrit :

I don't know how power meters report, but...

1
Int 2.Veff.Ieff.Sin(2.pi.t).Sin(2.pi.t + phi).dt = Veff.Ieff.Cos(phi)
0

Nothing new there. According to the power/VA definition, indeed you can
have PF ranging from -1 to +1. No pb with that.

But now, for one value of PF (positive or negative) you have two
possible phase values, one positive and one negative and if you wanted
to unambiguously qualify the current vs voltage relation you'd need to
tell both signed PF and leading/lagging.

Correct. Thank you Fred.
 
J

josephkk

Jan 1, 1970
0
Yes, I remember now using E a lot in college. I don't recall U so much,
but then I did undergraduate as a chemist where we were looking at work
function and chemical potentials. I mostly have forgotten more of that
than I remember.

I do still remember the difference between H2O and H2SO4...

Rick

Smarter than little Willie then.

;-)
 
J

josephkk

Jan 1, 1970
0
don't remember seeing ohm's law written other U=I*R in all my school
years

current isn't written as A(mpere) or C(urrent) either but I

-Lasse

Pretty much true, but i have seen current as J. Not quite the same thing
though, kind of a generalization for use with plasmas and Maxwell's laws.

?-)
 
J

josephkk

Jan 1, 1970
0
They say lots of weird things. I blame Lucas for the poor lighting
and all that warm beer they drink. It really messes with their minds!
;-)

They paid enough that they didn't have to watch their p's and q's
properly.

?-)
 
J

josephkk

Jan 1, 1970
0
So why do they want to replace the disk meters with digital ones? You
could add a VERY simple optical monitor to the disk meter to read the
number of revolutions and provide all the other benefits of digital
without the mess of the ADCs, etc. I suppose the old meters can be a
bit more expensive than the fancy, dancy digital ones?

Rick

Two things:

The way the certification process works.

They want new features that are not possible by just instrumenting
rotating disk types.

?-)
 
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