Help designing a low-noise TIA

[Jan Panteltje]

On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
<e4757abc-552f-4d44-ad56-001129e4c529@googlegroups.com>:

Hi all,

I am posting to this forum at the suggestion of George Herold from Teachspin,
he says you are the people to help me out. I understand a decent amount
about circuits, but not enough to design the low-noise TIA I would like to
build.

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect
that was one of the
first proofs that electrons inside metals carry the current.

In this experiment, a coil of wire is spun to high speeds and then braked rapidly.
The electrons keep moving and create a small pulse of current. Originally,
Tolman and Stewart used a ballistic galvanometer to act as a charge
amplifier and integrate the current to find the total charge.

I=E2=80=99d like to use a TIA to convert the small current pulse into a voltage,
then record that voltage as a function of time. The problem is that the
coil acts as a giant antenna and picks up all sorts of unwanted noise, so
I=E2=80=99d like to get rid of that noise. In particular, it is really good
at finding 60 Hz signals in the room.

Right now we=E2=80=99re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200 Ohm resistance,
500 mH inductance) to one input and put the other input across 200
Ohms to ground. The large amplification leads to huge amplification of the
noise, and it is hard to see our signal. We expect the current pulse to
be 1 nA of current, almost square wave in shape, and it should last the duration
of the braking, about 0.5 seconds.

Any suggestions appreciated!

--Matt Sullivan
Ithaca College Physics

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

So the experiment coil was loaded with about 40 Ohm.


It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...

In place of voltmeter perhap use a storage scope....
have a small one just right for this sort of thing:
http://panteltje.com/panteltje/pic/scope_pic/index.html

Or just digitize it at decent speed and then process it later,
a hum filter may work, better is to find a place away from mains cables and traffic,
how about a deserted island, now there you can have hula girls and bananas and sit in the sun zipping ..
oh well, get a budget for the trip, who knows...


The original article goes into depth about screening, very nice job, canceling the H and V earth magnetic fields.

Hey. ..

 

[whit3rd]

On Tuesday, June 4, 2019 at 6:06:22 PM UTC-7, John Larkin wrote:

A ballistic galvonmeter measured current, but that doesn't mean we
have to. I think the physics produces voltage.

A ballistic galvanometer is very slow; it measures integral of current,
i.e. charge.

A transimpedance amp might work, but so might a zero-ed active capacitor divider
(capacitor negative feedback becomes a hold capacitor). You could reverse the
polarity and run the experiment twice, to get rid of the inevitable offset voltage.

It just has to integrate for a half second during the deceleration, then hold for long
enough to get a reading. Relays for that kind of timing are easily arranged.

 

[whit3rd]

On Wednesday, June 5, 2019 at 11:29:50 AM UTC-7, Jan Panteltje wrote:

On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

So the experiment coil was loaded with about 40 Ohm.

A load seems unnecessary now (a century later). Just feed through a switch
directly into (-) input of an op amp, capacitor in feedback. That gives you circa
zero ohms, of course. The capacitor holds the charge, so output voltage is
equal to Q/C, with the switch ( relay?) open it can hold that value indefinitely.
Before applying the brake, a short across the hold capacitior (another switch: probably
a relay is best) will ensure that it starts off discharged.

There's still the coil resistance, of course.

Tolman was getting a nanocoulomb; a few hundred pF of capacitance will give a nicely
measurable voltage. His notes mention that the rotating apparatus works best if made of
wood; I wonder if a toy-top-drive, i.e. a pull string, would be the appropriate motor?
Probably a small voltmeter can be incorporated into the rotor, with batteries and such.

 

[John Larkin]

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
e4757abc-552f-4d44-ad56-001129e4c529@googlegroups.com>:

Hi all,

I am posting to this forum at the suggestion of George Herold from Teachspin,
he says you are the people to help me out. I understand a decent amount
about circuits, but not enough to design the low-noise TIA I would like to
build.

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect
that was one of the
first proofs that electrons inside metals carry the current.

In this experiment, a coil of wire is spun to high speeds and then braked rapidly.
The electrons keep moving and create a small pulse of current. Originally,
Tolman and Stewart used a ballistic galvanometer to act as a charge
amplifier and integrate the current to find the total charge.

I=E2=80=99d like to use a TIA to convert the small current pulse into a voltage,
then record that voltage as a function of time. The problem is that the
coil acts as a giant antenna and picks up all sorts of unwanted noise, so
I=E2=80=99d like to get rid of that noise. In particular, it is really good
at finding 60 Hz signals in the room.

Right now we=E2=80=99re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200 Ohm resistance,
500 mH inductance) to one input and put the other input across 200
Ohms to ground. The large amplification leads to huge amplification of the
noise, and it is hard to see our signal. We expect the current pulse to
be 1 nA of current, almost square wave in shape, and it should last the duration
of the braking, about 0.5 seconds.

Any suggestions appreciated!

--Matt Sullivan
Ithaca College Physics

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

So the experiment coil was loaded with about 40 Ohm.


It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.

You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...

The physics creates voltage. Why would anyone want to measure current?

This will be a very difficult thing to measure.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[whit3rd]

On Wednesday, June 5, 2019 at 3:57:11 PM UTC-7, John Larkin wrote:

The physics creates voltage. Why would anyone want to measure current?

This will be a very difficult thing to measure.

The voltage is in the range of errors in op amps, the current is far higher than
errors in op amps.

Also, the 'braking' results in a pulse; one wants to integrate the pulse,
not look at its dynamics, and current is easily integrated, onto a capacitor.

 

[John Larkin]

On Wed, 5 Jun 2019 17:48:09 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, June 5, 2019 at 2:29:50 PM UTC-4, Jan Panteltje wrote:
On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
e4757abc-552f-4d44-ad56-001129e4c529@googlegroups.com>:

Hi all,

I am posting to this forum at the suggestion of George Herold from Teachspin,
he says you are the people to help me out. I understand a decent amount
about circuits, but not enough to design the low-noise TIA I would like to
build.

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect
that was one of the
first proofs that electrons inside metals carry the current.

In this experiment, a coil of wire is spun to high speeds and then braked rapidly.
The electrons keep moving and create a small pulse of current. Originally,
Tolman and Stewart used a ballistic galvanometer to act as a charge
amplifier and integrate the current to find the total charge.

I=E2=80=99d like to use a TIA to convert the small current pulse into a voltage,
then record that voltage as a function of time. The problem is that the
coil acts as a giant antenna and picks up all sorts of unwanted noise, so
I=E2=80=99d like to get rid of that noise. In particular, it is really good
at finding 60 Hz signals in the room.

Right now we=E2=80=99re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200 Ohm resistance,
500 mH inductance) to one input and put the other input across 200
Ohms to ground. The large amplification leads to huge amplification of the
noise, and it is hard to see our signal. We expect the current pulse to
be 1 nA of current, almost square wave in shape, and it should last the duration
of the braking, about 0.5 seconds.

Any suggestions appreciated!

--Matt Sullivan
Ithaca College Physics

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!
Yeah! I think this is a fun experiment.

And extremely difficult. The people who have done this successfully
seem to have really worked at it.

I found another version that oscillated the coil rotationally on a
torsion bar and used a lock-in. That was hard too.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[George Herold]

On Wednesday, June 5, 2019 at 6:57:11 PM UTC-4, John Larkin wrote:

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
e4757abc-552f-4d44-ad56-001129e4c529@googlegroups.com>:

Hi all,

I am posting to this forum at the suggestion of George Herold from Teachspin,
he says you are the people to help me out. I understand a decent amount
about circuits, but not enough to design the low-noise TIA I would like to
build.

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect
that was one of the
first proofs that electrons inside metals carry the current.

In this experiment, a coil of wire is spun to high speeds and then braked rapidly.
The electrons keep moving and create a small pulse of current. Originally,
Tolman and Stewart used a ballistic galvanometer to act as a charge
amplifier and integrate the current to find the total charge.

I=E2=80=99d like to use a TIA to convert the small current pulse into a voltage,
then record that voltage as a function of time. The problem is that the
coil acts as a giant antenna and picks up all sorts of unwanted noise, so
I=E2=80=99d like to get rid of that noise. In particular, it is really good
at finding 60 Hz signals in the room.

Right now we=E2=80=99re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200 Ohm resistance,
500 mH inductance) to one input and put the other input across 200
Ohms to ground. The large amplification leads to huge amplification of the
noise, and it is hard to see our signal. We expect the current pulse to
be 1 nA of current, almost square wave in shape, and it should last the duration
of the braking, about 0.5 seconds.

Any suggestions appreciated!

--Matt Sullivan
Ithaca College Physics

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

So the experiment coil was loaded with about 40 Ohm.


It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.

Yeah, Matt, you've got a ~250 ohm source impedance,
you might as well take advantage of that.

You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...

The physics creates voltage. Why would anyone want to measure current?

This will be a very difficult thing to measure.

100 years ago current was the most sensitive thing to measure,
it's easy to get stuck in the past. :^)

George H.
(I think I suggested to Matt that if he wanted to measure current
he should use a TIA... so this may be my mistake....
A TIA needs a 'good' current source, with high input impedance.)



I ti

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Wed, 5 Jun 2019 17:04:04 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Wednesday, June 5, 2019 at 3:57:11 PM UTC-7, John Larkin wrote:

The physics creates voltage. Why would anyone want to measure current?

This will be a very difficult thing to measure.

The voltage is in the range of errors in op amps, the current is far higher than
errors in op amps.

The source looks like about 200 nV, 250 ohms, and some inductance. It
is not a current source. Calling it voltage or calling it current
doesn't matter, but the physics computes voltage.

That TIA probably won't work. A TIA doesn't magically make noise go
away.

I'd go for a good diffamp and use its CMRR to reject some noise. There
will be a lot of noise.

Also, the 'braking' results in a pulse; one wants to integrate the pulse,
not look at its dynamics, and current is easily integrated, onto a capacitor.

Why not digitize it and process mathematically? Why not look at
dynamics? That would be a good reality check. An integral is just one
number, and there are lots of good and bad ways to get there.

The fixed coil takes out ambient mag fields, so it's got to be
processed too.






--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[George Herold]

On Wednesday, June 5, 2019 at 2:29:50 PM UTC-4, Jan Panteltje wrote:

On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
e4757abc-552f-4d44-ad56-001129e4c529@googlegroups.com>:

Hi all,

I am posting to this forum at the suggestion of George Herold from Teachspin,
he says you are the people to help me out. I understand a decent amount
about circuits, but not enough to design the low-noise TIA I would like to
build.

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect
that was one of the
first proofs that electrons inside metals carry the current.

In this experiment, a coil of wire is spun to high speeds and then braked rapidly.
The electrons keep moving and create a small pulse of current. Originally,
Tolman and Stewart used a ballistic galvanometer to act as a charge
amplifier and integrate the current to find the total charge.

I=E2=80=99d like to use a TIA to convert the small current pulse into a voltage,
then record that voltage as a function of time. The problem is that the
coil acts as a giant antenna and picks up all sorts of unwanted noise, so
I=E2=80=99d like to get rid of that noise. In particular, it is really good
at finding 60 Hz signals in the room.

Right now we=E2=80=99re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200 Ohm resistance,
500 mH inductance) to one input and put the other input across 200
Ohms to ground. The large amplification leads to huge amplification of the
noise, and it is hard to see our signal. We expect the current pulse to
be 1 nA of current, almost square wave in shape, and it should last the duration
of the braking, about 0.5 seconds.

Any suggestions appreciated!

--Matt Sullivan
Ithaca College Physics

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

Yeah! I think this is a fun experiment.
Matt, if you want to see Jan's circuit, you need to find a little triangle
up in the RH corner and select 'show original'.

GH

So the experiment coil was loaded with about 40 Ohm.


It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...

In place of voltmeter perhap use a storage scope....
have a small one just right for this sort of thing:
http://panteltje.com/panteltje/pic/scope_pic/index.html

Or just digitize it at decent speed and then process it later,
a hum filter may work, better is to find a place away from mains cables and traffic,
how about a deserted island, now there you can have hula girls and bananas and sit in the sun zipping ..
oh well, get a budget for the trip, who knows...


The original article goes into depth about screening, very nice job, canceling the H and V earth magnetic fields.

Hey. ..

 

[John Larkin]

On Wed, 5 Jun 2019 18:10:08 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, June 5, 2019 at 6:57:11 PM UTC-4, John Larkin wrote:
On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
e4757abc-552f-4d44-ad56-001129e4c529@googlegroups.com>:

Hi all,

I am posting to this forum at the suggestion of George Herold from Teachspin,
he says you are the people to help me out. I understand a decent amount
about circuits, but not enough to design the low-noise TIA I would like to
build.

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect
that was one of the
first proofs that electrons inside metals carry the current.

In this experiment, a coil of wire is spun to high speeds and then braked rapidly.
The electrons keep moving and create a small pulse of current. Originally,
Tolman and Stewart used a ballistic galvanometer to act as a charge
amplifier and integrate the current to find the total charge.

I=E2=80=99d like to use a TIA to convert the small current pulse into a voltage,
then record that voltage as a function of time. The problem is that the
coil acts as a giant antenna and picks up all sorts of unwanted noise, so
I=E2=80=99d like to get rid of that noise. In particular, it is really good
at finding 60 Hz signals in the room.

Right now we=E2=80=99re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200 Ohm resistance,
500 mH inductance) to one input and put the other input across 200
Ohms to ground. The large amplification leads to huge amplification of the
noise, and it is hard to see our signal. We expect the current pulse to
be 1 nA of current, almost square wave in shape, and it should last the duration
of the braking, about 0.5 seconds.

Any suggestions appreciated!

--Matt Sullivan
Ithaca College Physics

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

So the experiment coil was loaded with about 40 Ohm.


It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.
Yeah, Matt, you've got a ~250 ohm source impedance,
you might as well take advantage of that.


You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...

The physics creates voltage. Why would anyone want to measure current?

This will be a very difficult thing to measure.
100 years ago current was the most sensitive thing to measure,
it's easy to get stuck in the past. :^)

Exactly.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Mike Perkins]

On 04/06/2019 20:28, ithacacollegephysics@gmail.com wrote:

Right now we’re using an OPA 140 with 1 GOhm and 10 pF as a feedback
resistor and capacitor in parallel. We attach the coil (about 200
Ohm resistance, 500 mH inductance) to one input and put the other
input across 200 Ohms to ground

That combination gives you a voltage gain (10e9/200) of 5,000,000

The input noise is 5.1 nV/sqrt(Hz)

So we should see 25mv/sqrt(Hz)

1GOhm and 10pF = 10ms / 100Hz

So a minimum of 250mV of white noise (above 10Hz)?

Given the 1/f noise is 250nVp-p, say 40nV rms; shouldn't we see
something like 2V rms of 1/f noise at the output?

Where am I going wrong?

--
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk

 

[George Herold]

On Wednesday, June 5, 2019 at 10:42:43 AM UTC-4, ithacacoll...@gmail.com wrote:

Hi all,

Thanks for the replies! A lot to think about.

If you want to see our setup, here is a picture:
https://www.dropbox.com/s/is3vdxlcz24ohml/TS-expt.jpg?dl=0

Here is the simple circuit we are working with now:
https://www.dropbox.com/s/f9aik177qqellcj/TS-ckt.jpg?dl=0
In the simulated circuit, we've added a current source to act as the electron motion upon braking the coil.

Phil, I am not sure I follow your suggestions, sorry. We'd put another coil outside the rotating coil to measure the signal from the rotating coil? Elaborations appreciated!

George, our coil is about 8" in diameter. I remember the Earth NMR from the Food Truck when it came to Ithaca College. If you look at our setup, we have something very similar: we have a second, stationary, coil directly below the rotating coil, and this coil is counter-wound. This definitely helps to reduce the 60 Hz noise (if there is other noise, it is drowned out by 60 Hz noise). At the time I thought our methods were essentially identical. Do you think a larger stationary coil surrounding the rotating coil would work better than a stationary coil of the same diameter beneath the rotating coil?

Jeorg, right now we reduce the remaining 60 Hz noise by simply averaging our voltage signal over 17 ms, so we get one data point for every 60 Hz cycle. This does reduce our noise. I planned to try to remove the 60 Hz noise via FFT and then fiter out the high frequencies, but I wanted to try and find an experimental solution first.

John Larkin, braking faster would be hard. The coil has about a pound of copper wire 8 inches from the rotation axis, and we spin it up to 6000 or 7000 rpm. It has a lot of angular momentum! Half a second is the best we've been able to do. And I am afraid we've worked pretty hard to get it spinning down even that quickly. As for the split coil, we have essentially done that with the rotating coil and the stationary coil. They can't both be rotating, or the signal we are hoping for cancels out (the electrons in the two coils are counter-rotating, so you get two pulses of current in opposite directions).

George, we did try a charge amplifier at first, which as far as I understand is the electronic analog of the ballistic galvanometer. But it was hard to get the op-amps to be stable and still be able to integrate over a whole second. So I figured we have much faster electronics now, so to get the total charge I can just integrate the current, so that's why we are trying a TIA now.

Matt, I'm still kinda confused about the coils (signal and compensating)
and the rotating contacts.. or whatever?

You've got the amp and batteries rotating on top of the signal coil?
Where is the compensating (60 Hz cancellation) coil?
And how do you contact it?

I our Earth's field thing, the two coils are in series.
I don't think the size matters that much... except the
compensation coil adds R and L to the input.

George H.

 

[Jan Panteltje]

On a sunny day (Wed, 5 Jun 2019 15:22:07 -0700 (PDT)) it happened whit3rd
<whit3rd@gmail.com> wrote in
<12a400fd-fa2d-48c6-98ce-38020a55bdea@googlegroups.com>:

On Wednesday, June 5, 2019 at 11:29:50 AM UTC-7, Jan Panteltje wrote:
On a sunny day (Tue, 4 Jun 2019 12:28:49 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in

We're trying to create a modern version of the Tolman-Stewart experiment
https://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect

From wikipedia I just did read the paper:
http://authors.library.caltech.edu/3372/1/TOLpr16b.pdf

Fun!

So the experiment coil was loaded with about 40 Ohm.

A load seems unnecessary now (a century later). Just feed through a switch
directly into (-) input of an op amp, capacitor in feedback. That gives you circa
zero ohms, of course. The capacitor holds the charge, so output voltage is
equal to Q/C, with the switch ( relay?) open it can hold that value indefinitely.
Before applying the brake, a short across the hold capacitior (another switch: probably
a relay is best) will ensure that it starts off discharged.

There's still the coil resistance, of course.

Tolman was getting a nanocoulomb; a few hundred pF of capacitance will give a nicely
measurable voltage. His notes mention that the rotating apparatus works best if made of
wood; I wonder if a toy-top-drive, i.e. a pull string, would be the appropriate motor?
Probably a small voltmeter can be incorporated into the rotor, with batteries and such.

Yes,
I find it really nice to see how they did those things with the available tools at that time.
I have used galvanometers, although that is a really long time ago.
Very nice and clever instruments.

 

[Jan Panteltje]

On a sunny day (Wed, 05 Jun 2019 15:56:17 -0700) it happened John Larkin
<jjlarkin@highland_snip_technology.com> wrote in
<jvhgfe9npk8bauedauu1582o2i8b6jeps0@4ax.com>:

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:
It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.


You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...
200E-9 * 900
= 0.000180

>The physics creates voltage. Why would anyone want to measure current?

Is not that what a galvanometer does, measure current?
Beta can be as high as 900 for some trannies.

>This will be a very difficult thing to measure.

Maybe in 1916 when the paper was published...


Collector current For an Rb of about 100 Ohm:
-> 900 * (200E-9 / 100) = 1.8e-06 is 1.8uA

1.8 uA in a 500 k collector resistor:
-> (900 * (200E-9 / 100)) * 500e3 = 0.9 Volt

Is not Linux wcalc cool

Fits nice in my storage scope ADC range using PIC 1.024V internal reference...
Or any multimeter of this age,

You can always use a darlington to get an other factor 900 ...
Zin does not go up the same ratio.


Using high impedances is often asking for interference trouble.



Math right?

 

[whit3rd]

On Wednesday, June 5, 2019 at 6:18:44 PM UTC-7, John Larkin wrote:

On Wed, 5 Jun 2019 17:04:04 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

Also, the 'braking' results in a pulse; one wants to integrate the pulse,
not look at its dynamics, and current is easily integrated, onto a capacitor.

Why not digitize it and process mathematically? Why not look at
dynamics? That would be a good reality check. An integral is just one
number, and there are lots of good and bad ways to get there.

That would require, though, instrumenting also the braking acceleration,
as a function of time, which is excess to needs. Simpler to just note the
initial velocity then stop it in a sub-second, and record the integrated current, the charge.

One measured rate, and a known 'full-stop' final condition, is sufficient information to
give the integral of the acceleration. So, it relates to integral of current from the (known)
source resistance. There's no reason to call it a 'current source' to make the result
meaningful, if we use an op amp's pseudoground (-) node as a lower-impedance-than-the-wire
current receiver.

 

[John Larkin]

On Thu, 6 Jun 2019 01:29:30 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Wednesday, June 5, 2019 at 6:18:44 PM UTC-7, John Larkin wrote:
On Wed, 5 Jun 2019 17:04:04 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

Also, the 'braking' results in a pulse; one wants to integrate the pulse,
not look at its dynamics, and current is easily integrated, onto a capacitor.

Why not digitize it and process mathematically? Why not look at
dynamics? That would be a good reality check. An integral is just one
number, and there are lots of good and bad ways to get there.

That would require, though, instrumenting also the braking acceleration,
as a function of time, which is excess to needs. Simpler to just note the
initial velocity then stop it in a sub-second, and record the integrated current, the charge.

In this experiment, both the original and modern versions, the real
signal is typically overwhelmed by artifacts. It would be easy to frob
around until you see the integral that you expect, declare victory,
and publish.

One measured rate, and a known 'full-stop' final condition, is sufficient information to
give the integral of the acceleration. So, it relates to integral of current from the (known)
source resistance. There's no reason to call it a 'current source' to make the result
meaningful, if we use an op amp's pseudoground (-) node as a lower-impedance-than-the-wire
current receiver.

And antenna.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Thu, 06 Jun 2019 06:22:45 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 05 Jun 2019 15:56:17 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
jvhgfe9npk8bauedauu1582o2i8b6jeps0@4ax.com>:

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:
It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.


You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...
200E-9 * 900
= 0.000180

The physics creates voltage. Why would anyone want to measure current?

Is not that what a galvanometer does, measure current?
Beta can be as high as 900 for some trannies.

This will be a very difficult thing to measure.

Maybe in 1916 when the paper was published...

There are papers online of modern versions. It's still really hard.

Collector current For an Rb of about 100 Ohm:
-> 900 * (200E-9 / 100) = 1.8e-06 is 1.8uA

1.8 uA in a 500 k collector resistor:
-> (900 * (200E-9 / 100)) * 500e3 = 0.9 Volt

Is not Linux wcalc cool

Fits nice in my storage scope ADC range using PIC 1.024V internal reference...
Or any multimeter of this age,

You can always use a darlington to get an other factor 900 ...
Zin does not go up the same ratio.


Using high impedances is often asking for interference trouble.



Math right?

You have computed a voltage gain of 4 million in a single transistor.
A reasonably biased single-transistor amp might have a gain around
200.

If I were doing this, I'd consider using a good NPN differential pair,
across the ends of the coil, running open-loop gain with the
collectors going into a cheap diffamp. Mount all that on the spinning
coil and bring out a big signal.

I think there are some really low-noise integrated diffamps too. ADI
has some around 1 nv/rthz, but 1/f really matters. Getting a clean
signal out of the spinning coil is really the hard part; the
electronics isn't difficult.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Thursday, June 6, 2019 at 9:38:14 AM UTC-4, John Larkin wrote:

On Thu, 06 Jun 2019 06:22:45 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 05 Jun 2019 15:56:17 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
jvhgfe9npk8bauedauu1582o2i8b6jeps0@4ax.com>:

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:
It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.


You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...
200E-9 * 900
= 0.000180

The physics creates voltage. Why would anyone want to measure current?

Is not that what a galvanometer does, measure current?
Beta can be as high as 900 for some trannies.

This will be a very difficult thing to measure.

Maybe in 1916 when the paper was published...

There are papers online of modern versions. It's still really hard.

I found this,
https://inis.iaea.org/collection/NCLCollectionStore/_Public/28/038/28038450.pdf?r=1&r=1

Which doesn't talk much about electronics.. but does talk about getting
leads to the rotating coil.

I'm still confused how Matt is making connections.
It seems like the local B-field is a problem too...
If that's the case then doing measurements in a city /building can be
made more difficult by all the moving pieces of iron... Cars,
trucks, elevators, etc. Which means the local B-field changes
in magnitude and direction by 1-2%. Maybe things are better late at night.
(when all good data is taken in my experience. :^)

George H.

Collector current For an Rb of about 100 Ohm:
-> 900 * (200E-9 / 100) = 1.8e-06 is 1.8uA

1.8 uA in a 500 k collector resistor:
-> (900 * (200E-9 / 100)) * 500e3 = 0.9 Volt

Is not Linux wcalc cool

Fits nice in my storage scope ADC range using PIC 1.024V internal reference...
Or any multimeter of this age,

You can always use a darlington to get an other factor 900 ...
Zin does not go up the same ratio.


Using high impedances is often asking for interference trouble.



Math right?

You have computed a voltage gain of 4 million in a single transistor.
A reasonably biased single-transistor amp might have a gain around
200.

If I were doing this, I'd consider using a good NPN differential pair,
across the ends of the coil, running open-loop gain with the
collectors going into a cheap diffamp. Mount all that on the spinning
coil and bring out a big signal.

I think there are some really low-noise integrated diffamps too. ADI
has some around 1 nv/rthz, but 1/f really matters. Getting a clean
signal out of the spinning coil is really the hard part; the
electronics isn't difficult.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Jan Panteltje]

On a sunny day (Thu, 06 Jun 2019 06:38:07 -0700) it happened John Larkin
<jjlarkin@highlandtechnology.com> wrote in
<hg4ife97ohgnjv01f0n9o8muhsqpt7oseb@4ax.com>:

On Thu, 06 Jun 2019 06:22:45 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 05 Jun 2019 15:56:17 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
jvhgfe9npk8bauedauu1582o2i8b6jeps0@4ax.com>:

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:
It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.


You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...
200E-9 * 900
= 0.000180

The physics creates voltage. Why would anyone want to measure current?

Is not that what a galvanometer does, measure current?
Beta can be as high as 900 for some trannies.

This will be a very difficult thing to measure.

Maybe in 1916 when the paper was published...

There are papers online of modern versions. It's still really hard.



Collector current For an Rb of about 100 Ohm:
-> 900 * (200E-9 / 100) = 1.8e-06 is 1.8uA

1.8 uA in a 500 k collector resistor:
-> (900 * (200E-9 / 100)) * 500e3 = 0.9 Volt

Is not Linux wcalc cool

Fits nice in my storage scope ADC range using PIC 1.024V internal reference...
Or any multimeter of this age,

You can always use a darlington to get an other factor 900 ...
Zin does not go up the same ratio.


Using high impedances is often asking for interference trouble.



Math right?

You have computed a voltage gain of 4 million in a single transistor.

Yes trannies are good!

A reasonably biased single-transistor amp might have a gain around
200.

Bad spwcimen?

If I were doing this, I'd consider using a good NPN differential pair,
across the ends of the coil, running open-loop gain with the
collectors going into a cheap diffamp. Mount all that on the spinning
coil and bring out a big signal.

Yes mounting it on the weel is perhaps a good idea, optical link to receiver?

I think there are some really low-noise integrated diffamps too. ADI
has some around 1 nv/rthz, but 1/f really matters. Getting a clean
signal out of the spinning coil is really the hard part; the
electronics isn't difficult.

Right, my circuit is simple

 

[John Larkin]

On Thu, 06 Jun 2019 13:57:16 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Thu, 06 Jun 2019 06:38:07 -0700) it happened John Larkin
jjlarkin@highlandtechnology.com> wrote in
hg4ife97ohgnjv01f0n9o8muhsqpt7oseb@4ax.com>:

On Thu, 06 Jun 2019 06:22:45 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 05 Jun 2019 15:56:17 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
jvhgfe9npk8bauedauu1582o2i8b6jeps0@4ax.com>:

On Wed, 05 Jun 2019 18:29:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:
It seems to me, if I was to tinker with that setup,
to make a 'ballistic' meter I would do something this

+9V +9V
| |
[ ] R1 o voltmeter +
|
|-------------------------o voltmeter -
| |
c |
coil + --- b NPN ===
e Q1 | C1
| |
/// ///

+9V
|
[ ] R2 5k6
|
coil - --------| +.7V
| |
| c
-- b NPN
e Q2
|
////

How it works:
A positive pulse on coil + results in base current in Q1
that is amplified and the collector current then discharges C1.
C1 will slowly recharge via R1,
The voltmeter indication is proportional to the current peak.
R1 sets the gain in a way, te hhigher teh moresensitve, 5k6 is a nice value.
Q2 creates a stable bias for Q1.

I think the expected signal is about 200 nV.


You are working with a very low impedance coil / source,
so can use a low impedance sensing system to actually get some current,
Using a high impedance sensor gives next to zero current.
Transistors are basically current amplifiers...
200E-9 * 900
= 0.000180

The physics creates voltage. Why would anyone want to measure current?

Is not that what a galvanometer does, measure current?
Beta can be as high as 900 for some trannies.

This will be a very difficult thing to measure.

Maybe in 1916 when the paper was published...

There are papers online of modern versions. It's still really hard.



Collector current For an Rb of about 100 Ohm:
-> 900 * (200E-9 / 100) = 1.8e-06 is 1.8uA

1.8 uA in a 500 k collector resistor:
-> (900 * (200E-9 / 100)) * 500e3 = 0.9 Volt

Is not Linux wcalc cool

Fits nice in my storage scope ADC range using PIC 1.024V internal reference...
Or any multimeter of this age,

You can always use a darlington to get an other factor 900 ...
Zin does not go up the same ratio.


Using high impedances is often asking for interference trouble.



Math right?

You have computed a voltage gain of 4 million in a single transistor.

Yes trannies are good!

Try it.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics