Sensing small inductances

On Sun, 25 Aug 2019 15:17:02 -0400, Joseph Gwinn
<joegwinn@comcast.net> wrote:

On Aug 25, 2019, Jan Panteltje wrote
(in article <qjuf09$uj9$1@dont-email.me&gt:

On a sunny day (Sun, 25 Aug 2019 11:07:04 -0500) it happened amdx
nojunk@knology.net> wrote in<qjubn7$aqf$1@dont-email.me>:

On 8/25/2019 12:24 AM, Jan Panteltje wrote:
On a sunny day (Sat, 24 Aug 2019 23:31:00 -0400) it happened bitrex
user@example.net> wrote in<Vhn8F.85134$9i3.23186@fx42.iad>:

http://panteltje.com/panteltje/pic/lc_pic/

Print and put in values.

Get a real monitor and /or see an eye doctor.

I can read them, but it isn´t always easy.
If you tell your camera that the picture is largely white, it will take far
better photos (by rendering the paper as white, versus 18% gray). Sometimes
one must lie to the camera to get it to do this, but a few experiments will
tell the tale.

Joe Gwinn

Use a good pen or pencil on white grid paper, and draw and letter
carefully.

I had to take two semisters of engineering drawing in college. We all
hated it and it was very valuable.

https://www.dropbox.com/s/qx9tabzj8ruit1f/Mirror_8.JPG?raw=1

 

[amdx]

On 8/25/2019 1:18 PM, Jan Panteltje wrote:

On a sunny day (25 Aug 2019 10:38:32 -0700) it happened Winfield Hill
winfieldhill@yahoo.com> wrote in <qjuh2o0v42@drn.newsguy.com>:

jlarkin@highlandsniptechnology.com wrote...

Jan Panteltje wrote:
amdx wrote
Jan Panteltje wrote:
bitrex wrote

http://panteltje.com/panteltje/pic/lc_pic/

Print and put in values.

Get a real monitor and /or see an eye doctor.

Your schematics are unreadable. I don't even try.

I'm often curious, but can not read them.
Jan, why are they so dark, with such a poor
contrast ratio? How do you even do that?

I dunno, I have no problem reading those in my browser,
or Linux 'xv' viewer or whatever,

Often I wonder (video is my background) if people even know how to adjust a monitor,
These pictures are of schematics I use to build the stuff,

I doubt you go back to your monitor when you build, you use your paper
schematic. If you are going to post schematics and we want you to,
why not make them readable by all those people that don't know how to
adjust their monitors. It's really not hard.
Is it just that you have had so many people tell you about the quality
of your schematics that you're not going to let them tell you what to
do? What, your 13 yrs old.

so 100% of info is there or it would have to be so obvious I omitted it.
I do not sell kits.
All the babble .. read the asm source it clearly shows in ASCII what is connected to what.
If anybody actually builds this thing they can ask.
The explanation text in the link I gave is 100% simple for anybody known in the art,

And if you cannot read it or understand it, so be it,

As to the art, if you cannot read a component value and understand what sort of magnitude say 'resistor' must be there
you need to do more experimenting, not so many silly simulations.

You're deflecting, your schematics are hard to read

Next somebody will say: 'Oh and I cannot read PIC asm..'
There is no end to not understanding
somebody once wrote something like 'hydrogen is the most present thing in the universe but for stupidity'
https://quoteinvestigator.com/2014/01/09/hydrogen/
different versions of it.

I am not referring to you, I know you know the stuff.
Jo.La. has a bunch of payed slaves working out details for him...
Some other one is into crystal radios and refuses to look up super-heterodyne
even offered me a deal LOL.
No hope there.

Hawaiian War Chant
https://www.youtube.com/watch?v=QY0ThFAp0Bc

Now help me on my inductor ferrite choice!
With love, Mikek

 

On Sun, 25 Aug 2019 13:59:58 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 24 Aug 2019 23:31:00 -0400, bitrex <user@example.net> wrote:

Microcontroller-based strategies like this work OK for high-Q inductances:

http://www.pa3fwm.nl/technotes/tn11b.html

But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.

I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")

and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.

It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.

For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.

The great little AADE meter has an oscillator circuit that always
oscillates, and a uP based frequency meter. It works very well for a
simple instrument, and does a few nH pretty well. The schematic is
online somewhere.

Making an oscillator is morally equivalent to boosting an inductor's
Q, and has the same problems at low Q.

Q is a function of frequency so whether the inductor needs its Q
boosted, or not, depends on what frequency you want it to oscillate at.

Most simple oscillator circuits don't tend to have enough loop gain to
make random scramble-wire inductance that might have a self-resonant
frequency in the hundreds of MHz ring reliably in a resonant tank down
at single-digit MHz frequencies a cheap uP could handle with its (cheap)
on-board peripherals.

A couple topologies like say the Pierce with things tuned exactly right
seem to sometimes, but naturally at <<< than the self resonant freq with
a low Q down there the freq stability over time and noise performance is
junk.

Inductors have ohmic losses and shunt capacitance that will fool any
simple instrument. I like to connect a function generator and a scope
across an inductor and sweep the frequency, to spot the region where
actual L dominates, then park in the middle of that region and
calculate L. And see the other stuff.

Really small Ls can be TDRd too.


Both fine techniques for the bench but not workable for a
production-thing with a tighter budget.

However what I'm mainly interested in being able to detect relative
differences between random-wires inductances with precision, and less
concern about absolute accuracy as compared to some reference standard.

Sounds like you could build an oscillator and measure frequencies.

Only slightly related, here's my latest oscillator design:

https://www.dropbox.com/s/5z3lgsovd7yqr9y/Trig_Osc_40M.jpg?raw=1

This (and some FPGA logic) replaces an obsolete Maxim tapped delay
line. It only needs to oscillate for five cycles.

 

[bitrex]

On 8/25/19 2:59 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 25 Aug 2019 14:06:54 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:34 PM, Jan Panteltje wrote:
On a sunny day (Sun, 25 Aug 2019 10:17:07 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
qig5med1kr6iqm86vk2gkogq157162qvp1@4ax.com>:

On Sun, 25 Aug 2019 17:02:59 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 25 Aug 2019 11:07:04 -0500) it happened amdx
nojunk@knology.net> wrote in <qjubn7$aqf$1@dont-email.me>:

On 8/25/2019 12:24 AM, Jan Panteltje wrote:
On a sunny day (Sat, 24 Aug 2019 23:31:00 -0400) it happened bitrex
user@example.net> wrote in <Vhn8F.85134$9i3.23186@fx42.iad>:

http://panteltje.com/panteltje/pic/lc_pic/


Print and put in values.

Get a real monitor and /or see an eye doctor.

Your schematics are unreadable. I don't even try.

You could learn something, but WTF do I care,
I do not use your products.


engineers looking at schematics like good gracious! why it's just awful!
/hand to forehead, swoon

I thought women were supposedly the dramatic ones

I thought engineering drawings were supposed to be clear and precise.
I assume he draws like that on purpose.

ps - your misogyny is apparent again

No, more like my sarcasm. It's not a thing I would say, but it is a
thing oppressed right-wing minorities like former Google employee James
Damore would write a whole paper on

 

On Sun, 25 Aug 2019 18:18:44 -0400, bitrex <user@example.net> wrote:

On 8/25/19 2:59 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 25 Aug 2019 14:06:54 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:34 PM, Jan Panteltje wrote:
On a sunny day (Sun, 25 Aug 2019 10:17:07 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
qig5med1kr6iqm86vk2gkogq157162qvp1@4ax.com>:

On Sun, 25 Aug 2019 17:02:59 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 25 Aug 2019 11:07:04 -0500) it happened amdx
nojunk@knology.net> wrote in <qjubn7$aqf$1@dont-email.me>:

On 8/25/2019 12:24 AM, Jan Panteltje wrote:
On a sunny day (Sat, 24 Aug 2019 23:31:00 -0400) it happened bitrex
user@example.net> wrote in <Vhn8F.85134$9i3.23186@fx42.iad>:

http://panteltje.com/panteltje/pic/lc_pic/


Print and put in values.

Get a real monitor and /or see an eye doctor.

Your schematics are unreadable. I don't even try.

You could learn something, but WTF do I care,
I do not use your products.


engineers looking at schematics like good gracious! why it's just awful!
/hand to forehead, swoon

I thought women were supposedly the dramatic ones

I thought engineering drawings were supposed to be clear and precise.
I assume he draws like that on purpose.

ps - your misogyny is apparent again


No, more like my sarcasm. It's not a thing I would say,

So why did you say it?

You meant it.

 

[bitrex]

On 8/25/19 5:57 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 25 Aug 2019 13:59:58 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 24 Aug 2019 23:31:00 -0400, bitrex <user@example.net> wrote:

Microcontroller-based strategies like this work OK for high-Q inductances:

http://www.pa3fwm.nl/technotes/tn11b.html

But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.

I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")

and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.

It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.

For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.

The great little AADE meter has an oscillator circuit that always
oscillates, and a uP based frequency meter. It works very well for a
simple instrument, and does a few nH pretty well. The schematic is
online somewhere.

Making an oscillator is morally equivalent to boosting an inductor's
Q, and has the same problems at low Q.

Q is a function of frequency so whether the inductor needs its Q
boosted, or not, depends on what frequency you want it to oscillate at.

Most simple oscillator circuits don't tend to have enough loop gain to
make random scramble-wire inductance that might have a self-resonant
frequency in the hundreds of MHz ring reliably in a resonant tank down
at single-digit MHz frequencies a cheap uP could handle with its (cheap)
on-board peripherals.

A couple topologies like say the Pierce with things tuned exactly right
seem to sometimes, but naturally at <<< than the self resonant freq with
a low Q down there the freq stability over time and noise performance is
junk.

Inductors have ohmic losses and shunt capacitance that will fool any
simple instrument. I like to connect a function generator and a scope
across an inductor and sweep the frequency, to spot the region where
actual L dominates, then park in the middle of that region and
calculate L. And see the other stuff.

Really small Ls can be TDRd too.


Both fine techniques for the bench but not workable for a
production-thing with a tighter budget.

However what I'm mainly interested in being able to detect relative
differences between random-wires inductances with precision, and less
concern about absolute accuracy as compared to some reference standard.

Sounds like you could build an oscillator and measure frequencies.

the client was hoping to measure small changes in inductance directly
from frequency counting but the raw differences at the lower frequencies
aren't large enough for his hardware to detect well. the tank needs to
be high Q to oscillate at all, reliably, but a high Q tank oscillation
frequency is insensitive to small changes in the inductance, unless the
inductance is very small with respect to the capacitance. but too large
a cap with respect to the inductance wrecks the Q, also. it's an
irritating prison of constraints that are annoying to try to work
around, to force it that way.

I think changing the whole resonant frequency by doing capacitor swap
and a "differential" measurement doing the math in software as Jan
suggested will likely work.

Only slightly related, here's my latest oscillator design:

https://www.dropbox.com/s/5z3lgsovd7yqr9y/Trig_Osc_40M.jpg?raw=1

This (and some FPGA logic) replaces an obsolete Maxim tapped delay
line. It only needs to oscillate for five cycles.

 

[bitrex]

On 8/25/19 6:49 PM, jlarkin@highlandsniptechnology.com wrote:

engineers looking at schematics like good gracious! why it's just awful!
/hand to forehead, swoon

I thought women were supposedly the dramatic ones

I thought engineering drawings were supposed to be clear and precise.
I assume he draws like that on purpose.

ps - your misogyny is apparent again


No, more like my sarcasm. It's not a thing I would say,

So why did you say it?

You meant it.

I'll gladly tell my girl friend a right wing engineering professional on
the internet said I was a misogynist, I expect she'll probably roll her
eyes and laugh in the way she usually does when from time to time I show
her some of the right-wing rants that pop up here lol. Hold up I'm gonna
show her the whole thread right now. brb.

 

On Sun, 25 Aug 2019 19:07:33 -0400, bitrex <user@example.net> wrote:

On 8/25/19 5:57 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 25 Aug 2019 13:59:58 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 24 Aug 2019 23:31:00 -0400, bitrex <user@example.net> wrote:

Microcontroller-based strategies like this work OK for high-Q inductances:

http://www.pa3fwm.nl/technotes/tn11b.html

But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.

I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")

and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.

It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.

For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.

The great little AADE meter has an oscillator circuit that always
oscillates, and a uP based frequency meter. It works very well for a
simple instrument, and does a few nH pretty well. The schematic is
online somewhere.

Making an oscillator is morally equivalent to boosting an inductor's
Q, and has the same problems at low Q.

Q is a function of frequency so whether the inductor needs its Q
boosted, or not, depends on what frequency you want it to oscillate at.

Most simple oscillator circuits don't tend to have enough loop gain to
make random scramble-wire inductance that might have a self-resonant
frequency in the hundreds of MHz ring reliably in a resonant tank down
at single-digit MHz frequencies a cheap uP could handle with its (cheap)
on-board peripherals.

A couple topologies like say the Pierce with things tuned exactly right
seem to sometimes, but naturally at <<< than the self resonant freq with
a low Q down there the freq stability over time and noise performance is
junk.

Inductors have ohmic losses and shunt capacitance that will fool any
simple instrument. I like to connect a function generator and a scope
across an inductor and sweep the frequency, to spot the region where
actual L dominates, then park in the middle of that region and
calculate L. And see the other stuff.

Really small Ls can be TDRd too.


Both fine techniques for the bench but not workable for a
production-thing with a tighter budget.

However what I'm mainly interested in being able to detect relative
differences between random-wires inductances with precision, and less
concern about absolute accuracy as compared to some reference standard.

Sounds like you could build an oscillator and measure frequencies.

the client was hoping to measure small changes in inductance directly
from frequency counting but the raw differences at the lower frequencies
aren't large enough for his hardware to detect well. the tank needs to
be high Q to oscillate at all, reliably, but a high Q tank oscillation
frequency is insensitive to small changes in the inductance, unless the
inductance is very small with respect to the capacitance.

A high-Q LC oscillator follows the resonance equation even closer than
a low-Q one. w = 1/root(LC)

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

A high-Q LC oscillator follows the resonance equation even closer than
a low-Q one.

w = 1/root(LC)

With infinite Q.

For ordinary inductors, the ratio of the actual resonant frequency to the
thoretical resonant frequency is root(1 - 1/(4Q^2)). In practise, a Q of 10
gives an actual frequency of 99.87% of theoretical.

See Radiotron_Designers_Handbook_1954.pdf 90.6MB

<http://preview.tinyurl.com/hmnpj2r>

See EQ 3 on page 449. This explains the variation in resonant frequency
with Q. I have not been able to find this information anywhere else.

 

[bitrex]

On 8/25/19 7:45 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 25 Aug 2019 19:07:33 -0400, bitrex <user@example.net> wrote:

On 8/25/19 5:57 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 25 Aug 2019 13:59:58 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 24 Aug 2019 23:31:00 -0400, bitrex <user@example.net> wrote:

Microcontroller-based strategies like this work OK for high-Q inductances:

http://www.pa3fwm.nl/technotes/tn11b.html

But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.

I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")

and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.

It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.

For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.

The great little AADE meter has an oscillator circuit that always
oscillates, and a uP based frequency meter. It works very well for a
simple instrument, and does a few nH pretty well. The schematic is
online somewhere.

Making an oscillator is morally equivalent to boosting an inductor's
Q, and has the same problems at low Q.

Q is a function of frequency so whether the inductor needs its Q
boosted, or not, depends on what frequency you want it to oscillate at.

Most simple oscillator circuits don't tend to have enough loop gain to
make random scramble-wire inductance that might have a self-resonant
frequency in the hundreds of MHz ring reliably in a resonant tank down
at single-digit MHz frequencies a cheap uP could handle with its (cheap)
on-board peripherals.

A couple topologies like say the Pierce with things tuned exactly right
seem to sometimes, but naturally at <<< than the self resonant freq with
a low Q down there the freq stability over time and noise performance is
junk.

Inductors have ohmic losses and shunt capacitance that will fool any
simple instrument. I like to connect a function generator and a scope
across an inductor and sweep the frequency, to spot the region where
actual L dominates, then park in the middle of that region and
calculate L. And see the other stuff.

Really small Ls can be TDRd too.


Both fine techniques for the bench but not workable for a
production-thing with a tighter budget.

However what I'm mainly interested in being able to detect relative
differences between random-wires inductances with precision, and less
concern about absolute accuracy as compared to some reference standard.

Sounds like you could build an oscillator and measure frequencies.

the client was hoping to measure small changes in inductance directly
from frequency counting but the raw differences at the lower frequencies
aren't large enough for his hardware to detect well. the tank needs to
be high Q to oscillate at all, reliably, but a high Q tank oscillation
frequency is insensitive to small changes in the inductance, unless the
inductance is very small with respect to the capacitance.

A high-Q LC oscillator follows the resonance equation even closer than
a low-Q one. w = 1/root(LC)

Right what I mean is that you can "nudge" the frequency of a low-Q
oscillating tank made with an inductor that has intrinsically low Q in
that frequency area, around easier to wider deviation by say physically
stretching or compressing an air-core coil, assuming there's enough
overall amplifier gain in the bandwidth of interest to keep it spinning,
because the loop gain skirt is relatively broad. this also means that
its long term frequency stability and short-term phase noise sucks.

Or you can use negative resistance or something to boost the lossy
inductor's intrinsic Q up, and thusly the Q of the tank. however since Q
is a function of frequency a fixed negative R only really works good in
the area of a single resonant frequency. A high-Q tank's gain skirt
plunges very quickly off-resonance, the ESR-lossy rapidly dominates
again and it drops out of oscillation.

 

[bitrex]

On 8/25/19 9:41 PM, bitrex wrote:

On 8/25/19 7:45 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 25 Aug 2019 19:07:33 -0400, bitrex <user@example.net> wrote:

On 8/25/19 5:57 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 25 Aug 2019 13:59:58 -0400, bitrex <user@example.net> wrote:

On 8/25/19 1:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 24 Aug 2019 23:31:00 -0400, bitrex <user@example.net> wrote:

Microcontroller-based strategies like this work OK for high-Q
inductances:

http://www.pa3fwm.nl/technotes/tn11b.html

But don't work too good for little random-wire very lossy
inductances,
of values around 0.5uH to 5uH, at the lower excitation
frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.

I was thinking the small inductance could have its effective Q
boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they
all
obv. tend towards being unstable and are "fiddly" and I'm
uncomfortable
using them in "real work")

and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase
detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.

It might need little external hardware other than the Q-booster
in some
implementation. Clock out to the tank and leading/lagging phase
signal
back in to the uP to an onboard comparator/phase detector and
integrator.

For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.

The great little AADE meter has an oscillator circuit that always
oscillates, and a uP based frequency meter. It works very well for a
simple instrument, and does a few nH pretty well. The schematic is
online somewhere.

Making an oscillator is morally equivalent to boosting an inductor's
Q, and has the same problems at low Q.

Q is a function of frequency so whether the inductor needs its Q
boosted, or not, depends on what frequency you want it to oscillate
at.

Most simple oscillator circuits don't tend to have enough loop gain to
make random scramble-wire inductance that might have a self-resonant
frequency in the hundreds of MHz ring reliably in a resonant tank down
at single-digit MHz frequencies a cheap uP could handle with its
(cheap)
on-board peripherals.

A couple topologies like say the Pierce with things tuned exactly
right
seem to sometimes, but naturally at <<< than the self resonant freq
with
a low Q down there the freq stability over time and noise
performance is
junk.

Inductors have ohmic losses and shunt capacitance that will fool any
simple instrument. I like to connect a function generator and a scope
across an inductor and sweep the frequency, to spot the region where
actual L dominates, then park in the middle of that region and
calculate L. And see the other stuff.

Really small Ls can be TDRd too.


Both fine techniques for the bench but not workable for a
production-thing with a tighter budget.

However what I'm mainly interested in being able to detect relative
differences between random-wires inductances with precision, and less
concern about absolute accuracy as compared to some reference
standard.

Sounds like you could build an oscillator and measure frequencies.

the client was hoping to measure small changes in inductance directly
from frequency counting but the raw differences at the lower
frequencies aren't large enough for his hardware to detect well. the
tank needs to
be high Q to oscillate at all, reliably, but a high Q tank oscillation
frequency is insensitive to small changes in the inductance, unless the
inductance is very small with respect to the capacitance.

A high-Q LC oscillator follows the resonance equation even closer than
a low-Q one. w = 1/root(LC)


Right what I mean is that you can "nudge" the frequency of a low-Q
oscillating tank made with an inductor that has intrinsically low Q in
that frequency area, around easier to wider deviation by say physically
stretching or compressing an air-core coil, assuming there's enough
overall amplifier gain in the bandwidth of interest to keep it spinning,
 because the loop gain skirt is relatively broad. this also means that
its long term frequency stability and short-term phase noise sucks.

Or you can use negative resistance or something to boost the lossy
inductor's intrinsic Q up, and thusly the Q of the tank. however since Q
is a function of frequency a fixed negative R only really works good in
the area of a single resonant frequency. A high-Q tank's gain skirt
plunges very quickly off-resonance, the ESR-lossy rapidly dominates
again and it drops out of oscillation.

a more elegant solution on paper is to use a negative capacitance
instead of a negative resistance to boost the Q of a lossy tank. but all
real-world negative impedance circuits love to mis-behave, all of these
negative impedance circuits are academic exercises and useless for real
work as-drawn:
<https://en.wikipedia.org/wiki/Negative_impedance_converter#Negative_impedance_circuits>

 

[Jeroen Belleman]

bitrex wrote:

a more elegant solution on paper is to use a negative capacitance
instead of a negative resistance to boost the Q of a lossy tank. but all
real-world negative impedance circuits love to mis-behave, all of these
negative impedance circuits are academic exercises and useless for real
work as-drawn:
https://en.wikipedia.org/wiki/Negative_impedance_converter#Negative_impedance_circuits

It's all a matter of perspective. If you work out the impedance
of an oscillator circuit from the viewpoint of the resonator,
you'll get a negative resistance.

I don't see the point of negative capacitance. Increasing the
Q implies reducing or compensating losses. A reactive component
doesn't do that.

Jeroen Belleman

 

[piglet]

On 25/08/2019 04:31, bitrex wrote:

Microcontroller-based strategies like this work OK for high-Q inductances:

http://www.pa3fwm.nl/technotes/tn11b.html

But don't work too good for little random-wire very lossy inductances,
of values around 0.5uH to 5uH, at the lower excitation frequencies that
microprocessors can easily provide from direct pin-switching system
clock-derived outputs. e.g. inductaors that have self-resonant
frequencies in the 100s of MHz.

I was thinking the small inductance could have its effective Q boosted
via boostrapping, perhaps (I'm kinda down on negative impedance
circuits, now, you can make some cute circuits with them but they all
obv. tend towards being unstable and are "fiddly" and I'm uncomfortable
using them in "real work")

and then you could measure a certain range of small inductances by
applying a clock to a tank circuit thru a resistor, and putting the
original clock plus the output from the tank into a phase detector a la
a PLL and look at the integrated leading or lagging phase "up/down"
signal to infer the inductance.

It might need little external hardware other than the Q-booster in some
implementation. Clock out to the tank and leading/lagging phase signal
back in to the uP to an onboard comparator/phase detector and integrator.

For my particular solution needs whatever form it takes, it would be
best to trade of absolute accuracy for precision/repeatability.

A problem with measuring inductance by making the DUT part of an
oscillator tank and measuring frequency is the square root relationship
works against you by compressing sensitivity.

What you could try is adapting the Boonton 72 capacitance meter topology
to measure inductance. A fixed frequency low current source feeds the
DUT into a calibrated resonant LC in the test instrument, amplify and
measure with quadrature synchronous detector. RF techniques rather than
time domain!

The Boonton 72 can resolve tiny capacitance changes so I expect a C to L
transformed version might also be capable of resolving tiny inductance
changes?

piglet

 

[bitrex]

On 8/26/19 2:32 AM, Jeroen Belleman wrote:

bitrex wrote:
[Snip!]
a more elegant solution on paper is to use a negative capacitance
instead of a negative resistance to boost the Q of a lossy tank. but
all real-world negative impedance circuits love to mis-behave, all of
these negative impedance circuits are academic exercises and useless
for real work as-drawn:
https://en.wikipedia.org/wiki/Negative_impedance_converter#Negative_impedance_circuits


It's all a matter of perspective. If you work out the impedance
of an oscillator circuit from the viewpoint of the resonator,
you'll get a negative resistance.

only if it's already oscillating - if the coil is so low Q that it won't
even start then there's no negative-nothing, nowhere!

I don't see the point of negative capacitance. Increasing the
Q implies reducing or compensating losses. A reactive component
doesn't do that.

Jeroen Belleman

a negative capacitance has to be powered to operate; the charge goes
down but the voltage (and thus 1/2CV^2 energy) goes up, that requires it
to get some energy from somewhere the system didn't have before. No such
thing as a passive negative capacitance that behaves just like a
positive passive capacitance with its sign flipped and still conserves
the total energy of the system that I know of. so long as it's not all
returned to the source in a purely reactive system that excess is then
available to do work.

in an electronic negative capacitance circuit the physical capacitor in
the feedback loop is of course always acting like a regular capacitance
so the idea of "charge" is kind of a metaphor I think but the whole
system is behaving like a negative one.

 

[bitrex]

On 8/26/19 4:22 AM, bitrex wrote:

On 8/26/19 2:32 AM, Jeroen Belleman wrote:
bitrex wrote:
[Snip!]
a more elegant solution on paper is to use a negative capacitance
instead of a negative resistance to boost the Q of a lossy tank. but
all real-world negative impedance circuits love to mis-behave, all of
these negative impedance circuits are academic exercises and useless
for real work as-drawn:
https://en.wikipedia.org/wiki/Negative_impedance_converter#Negative_impedance_circuits


It's all a matter of perspective. If you work out the impedance
of an oscillator circuit from the viewpoint of the resonator,
you'll get a negative resistance.

only if it's already oscillating - if the coil is so low Q that it won't
even start then there's no negative-nothing, nowhere!

I don't see the point of negative capacitance. Increasing the
Q implies reducing or compensating losses. A reactive component
doesn't do that.

Jeroen Belleman

a negative capacitance has to be powered to operate; the charge goes
down but the voltage (and thus 1/2CV^2 energy) goes up, that requires it
to get some energy from somewhere the system didn't have before. No such
thing as a passive negative capacitance that behaves just like a
positive passive capacitance with its sign flipped and still conserves
the total energy of the system that I know of.

For small-signal analysis I guess it's OK to treat them that way, small
signal analysis assumes an infinitesimal signal and so the energy
required is an infinitesimal too.

 

[Jeroen Belleman]

bitrex wrote:

On 8/26/19 2:32 AM, Jeroen Belleman wrote:
bitrex wrote:
[Snip!]
a more elegant solution on paper is to use a negative capacitance
instead of a negative resistance to boost the Q of a lossy tank. but
all real-world negative impedance circuits love to mis-behave, all of
these negative impedance circuits are academic exercises and useless
for real work as-drawn:
https://en.wikipedia.org/wiki/Negative_impedance_converter#Negative_impedance_circuits


It's all a matter of perspective. If you work out the impedance
of an oscillator circuit from the viewpoint of the resonator,
you'll get a negative resistance.

only if it's already oscillating - if the coil is so low Q that it won't
even start then there's no negative-nothing, nowhere!

Sigh.

I don't see the point of negative capacitance. Increasing the
Q implies reducing or compensating losses. A reactive component
doesn't do that.

Jeroen Belleman

a negative capacitance has to be powered to operate; the charge goes
down but the voltage (and thus 1/2CV^2 energy) goes up, that requires it
to get some energy from somewhere the system didn't have before. No such
thing as a passive negative capacitance that behaves just like a
positive passive capacitance with its sign flipped and still conserves
the total energy of the system that I know of. so long as it's not all
returned to the source in a purely reactive system that excess is then
available to do work.

A negative capacitance indeed has to be a powered active circuit,
however, to provide nett energy, it is necessary to have a negative
real component in the impedance. A purely reactive impedance,
negative or not, does not provide or absorb nett work. That's the
*definition* of a reactive impedance.

in an electronic negative capacitance circuit the physical capacitor in
the feedback loop is of course always acting like a regular capacitance
so the idea of "charge" is kind of a metaphor I think but the whole
system is behaving like a negative one.

OK.

Jeroen Belleman

 

[whit3rd]

On Sunday, August 25, 2019 at 4:45:45 PM UTC-7, jla...@highlandsniptechnology.com wrote:

A high-Q LC oscillator follows the resonance equation even closer than
a low-Q one. w = 1/root(LC)

But, any LC oscillator only has 0.5% frequency change for a 1% inductance change.
It's a weaker dependence than, say, an L-R oscillator.

An oscillator, LR circuit, and thermal measure of the resistor temperature rise
would be pretty much foolproof, and if the inductive conductance is high,
the back-emf will have square-law effect on the resistor heating.

 

[Martin Brown]

On 25/08/2019 18:38, Winfield Hill wrote:

jlarkin@highlandsniptechnology.com wrote...

Jan Panteltje wrote:
amdx wrote
Jan Panteltje wrote:
bitrex wrote

http://panteltje.com/panteltje/pic/lc_pic/

Print and put in values.

Get a real monitor and /or see an eye doctor.

Your schematics are unreadable. I don't even try.

I'm often curious, but can not read them.
Jan, why are they so dark, with such a poor
contrast ratio? How do you even do that?

The lousy contrast wouldn't be so bad if the illumination was a bit more
uniform, but the combination of uneven lighting, crumpled paper and dark
top right corner defeats most histogram equalisation. The JPEG artifacts
and low light colour noise do it no favours at all.

It would also be around 200k as a greyscale PNG if correctly exposed.

Anyone who wants to read the circuit diagram should try convert to
greyscale, histogram equalisation to make the (presumed) white paper
white followed by unsharp masking to bring out the faint pencil lines.

Expect to lose some detail in the dark areas...

--
Regards,
Martin Brown

 

[Joseph Gwinn]

On Aug 25, 2019, Steve Wilson wrote
(in article<XnsAAB6DCA0C5932idtokenpost@69.16.179.23&gt:

jlarkin@highlandsniptechnology.com wrote:

A high-Q LC oscillator follows the resonance equation even closer than
a low-Q one.

w = 1/root(LC)

With infinite Q.

For ordinary inductors, the ratio of the actual resonant frequency to the
thoretical resonant frequency is root(1 - 1/(4Q^2)). In practise, a Q of 10
gives an actual frequency of 99.87% of theoretical.

See Radiotron_Designers_Handbook_1954.pdf 90.6MB

http://preview.tinyurl.com/hmnpj2r

See EQ 3 on page 449. This explains the variation in resonant frequency
with Q. I have not been able to find this information anywhere else.

I have seen it elsewhere, in old textbooks. It may be in Terman.

Joe Gwinn

 

[bitrex]

On 8/26/19 5:25 AM, Jeroen Belleman wrote:

I don't see the point of negative capacitance. Increasing the
Q implies reducing or compensating losses. A reactive component
doesn't do that.

Jeroen Belleman

a negative capacitance has to be powered to operate; the charge goes
down but the voltage (and thus 1/2CV^2 energy) goes up, that requires
it to get some energy from somewhere the system didn't have before. No
such thing as a passive negative capacitance that behaves just like a
positive passive capacitance with its sign flipped and still conserves
the total energy of the system that I know of. so long as it's not all
returned to the source in a purely reactive system that excess is then
available to do work.

A negative capacitance indeed has to be a powered active circuit,

There are some naturally-occurring structures e.g. in ferroelectric
crystals that also exhibit negative capacitance they require energy from
somewhere, too

however, to provide nett energy, it is necessary to have a negative real
component in the impedance. A purely reactive impedance,
negative or not, does not provide or absorb nett work. That's the
*definition* of a reactive impedance.

who cares what the academic definition of a "purely reactive" negative
capacitance is, they don't exist, the electronic ones can compensate
tank circuit losses just fine just like a negative resistance but they
don't have DC gain which can be a nice feature to have

in an electronic negative capacitance circuit the physical capacitor
in the feedback loop is of course always acting like a regular
capacitance so the idea of "charge" is kind of a metaphor I think but
the whole system is behaving like a negative one.

OK.

Jeroen Belleman