You're still doing it. Paul (I think) said "measure" and Bill, no, looks
like Len (I think) said "finding", meaning "calculating".


"Avery Fineman" wrote in message
...
In article , Bill Turner
writes:

On Sun, 07 Dec 2003 13:55:35 +0200, Paul Keinanen
wrote:

.snip
Not only can you *not* measure them separately, they can not be
physically separated either, since the parasitic capacitance is always
present between adjacent windings....


Nonsense. General Radio had a nice little formula way back
before 1956 for finding the distributed capacity of an inductor.
Len Anderson
retired (from regular hours) electronic engineer person

OOPS Bill. By the formula, change F and Xl changes! Avery said below;
"reactance changes with frequency" and is correct. Also, if you change L
then Xl changes, but that is not what he said.

--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

__________________________________________________ _______

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

How could you possibly define it otherwise?
--
Bill, W6WRT

OOPS Bill. By the formula, change F and Xl changes! Avery said below;
"reactance changes with frequency" and is correct. Also, if you change L
then Xl changes, but that is not what he said.

--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

__________________________________________________ _______

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

How could you possibly define it otherwise?
--
Bill, W6WRT

Ahhhh! So there does seem to be a mis interpretation of the formula
here.-Steve

Bill,
I believe you are placing the dependant and independent variables in the
wrong place. The Xl is the dependant variable. Xl *depends upon* F and L,
not the other way around. That is, given an L and F you calculate the X.
X is the answer.
Only if you know there are no other contributing factors can the formula
be used the other way, because it does not factor them (the parasitic
capacitance) in. That is, Given an X measurement you can not tell the
inductance, only the *equivalent total* inductive reactance.


--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid. Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

--
Bill, W6WRT

Ahhhh! So there does seem to be a mis interpretation of the formula
here.-Steve

Bill,
I believe you are placing the dependant and independent variables in the
wrong place. The Xl is the dependant variable. Xl *depends upon* F and L,
not the other way around. That is, given an L and F you calculate the X.
X is the answer.
Only if you know there are no other contributing factors can the formula
be used the other way, because it does not factor them (the parasitic
capacitance) in. That is, Given an X measurement you can not tell the
inductance, only the *equivalent total* inductive reactance.


--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid. Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

--
Bill, W6WRT

There'something sour here. Way down ...


"Paul Keinanen" wrote in message
...
[snip]
The problem with circuits containing both inductances and capacitances
is that in one kind of reactance, there is a +90 degree phase shift
and the other with -90 degree phase shift. Thus, when these are
combined, they partially cancel each other, producing different
magnitudes and some phase shift between -90 and +90 degrees. If only
the resultant magnitude is used (and the resultant phase is ignored),
this would give the false impression that the inductance changes with
frequency.

I don't quite follow where you are going here. below the self resonant
freq the angle will be +90 (minus a little for what ever resistance is
there).


The rest of this about measuring the energy from DC, I don't think is at all
practical.

[snip] the inductance could be measured in a different way.
... the energy
stored in the inductance is W = I*I*L/2. ...
...cut the DC current...dissipate the energy in some kind of
integrating load across L. Even if there is a significant
capacitance[snip]
...the energy would bounce back
between L and C, but finally it would be dissipated by the external
load. ...
Thus using this measurement method, the value of L would be the same
regardless if C is present or not....

Paul OH3LWR

OK. so then, how do you propose to measure this energy? I don't think
it is practical.


--
Steve N, K,9
d, c. i

There'something sour here. Way down ...


"Paul Keinanen" wrote in message
...
[snip]
The problem with circuits containing both inductances and capacitances
is that in one kind of reactance, there is a +90 degree phase shift
and the other with -90 degree phase shift. Thus, when these are
combined, they partially cancel each other, producing different
magnitudes and some phase shift between -90 and +90 degrees. If only
the resultant magnitude is used (and the resultant phase is ignored),
this would give the false impression that the inductance changes with
frequency.

I don't quite follow where you are going here. below the self resonant
freq the angle will be +90 (minus a little for what ever resistance is
there).


The rest of this about measuring the energy from DC, I don't think is at all
practical.

[snip] the inductance could be measured in a different way.
... the energy
stored in the inductance is W = I*I*L/2. ...
...cut the DC current...dissipate the energy in some kind of
integrating load across L. Even if there is a significant
capacitance[snip]
...the energy would bounce back
between L and C, but finally it would be dissipated by the external
load. ...
Thus using this measurement method, the value of L would be the same
regardless if C is present or not....

Paul OH3LWR

OK. so then, how do you propose to measure this energy? I don't think
it is practical.


--
Steve N, K,9
d, c. i

On Tue, 09 Dec 2003 09:19:23 -0800, Bill Turner
wrote:

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

Measurement errors? I don't know enough about your way of working to
say. But thanks for giving your worked example. It'll no doubt help to
pin down the exact area of disagreement between us.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

On Tue, 09 Dec 2003 09:19:23 -0800, Bill Turner
wrote:

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

Measurement errors? I don't know enough about your way of working to
say. But thanks for giving your worked example. It'll no doubt help to
pin down the exact area of disagreement between us.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

--
Bill, W6WRT

The inductance is not changing. What you are measuring is not pure
inductance but the coil has a stray capacitance. That is what is making the
coil seof resonate.

YOu did not say what hapens at 110 mhz, 200 mhz, and 500 mhz, if you did ,
it would measuer capacitance reactance. How do you change a coil into a
capacitor ? You don't , but the effect of reactance has.

Look at it this from a totally differant angle. You stick the leads of a DV
voltmeter in the wall socket. It does not show any deflection other than
maybe the first jump when it is plugged in. Does that mean there is no
voltage or power in the circuit, I think not. Stick your fingers in it and
see what hapens :-)

Your method is flawed in the same way, you only measured inductance ( not
really that , but the inductive reactance at a given frequency, but did not
measuer capcitance. Where did the capacitance come from ? It is what makes
the coil selfresonante. If you measuer a circuit that has inductance,
capacitance and resistance, depending on if it is series or pareallel
resonate here is what will hapen. As the frequency is increaced the
inductance reactance will increace, it will measuer resistance at the
reosnant frequency , then a large capacitance reactance and then a small
capacitance reactance or else the reverse will hapen, capacitive reactance,
resisstance, inductive reactance. However none of the actual inductance,
capacitance or resistance values will change. YOu are confusing inductacne
and reactance.

YOu are only seeing one part of the big picture. YOu have to look at
several formulars to see what is going on in a circuit that has inductance
and capacitance.