Help designing a low-noise TIA

[Joseph Gwinn]

On Jun 7, 2019, whit3rd wrote
(in article<f4eb199d-086c-4be0-8fe2-8dc37a36ab7e@googlegroups.com&gt:

On Friday, June 7, 2019 at 8:55:17 AM UTC-7, George Herold wrote:
On Thursday, June 6, 2019 at 11:27:28 PM UTC-4, John Larkin wrote:

The mercotac things use "liquid metal" contacts. What metal is
liquid??
Mercury? Gallium if you heat it a little, I wonder if there is a temperature
spec.?

I'd expect some healthy thermoelectrics.

If you put a battery and op amp into the spinning disk, the rotating
contacts can have the buffered integrator-capacitor voltage
on them, so a few microvolts won't matter. The nanovolt signals don't
need to pass through the mystery metals.

And no one's mentioned 1/f noise.

Noise only makes a single run uncertain, multiple runs will solve that.

For gaussian noise and the like, averaging does help. For 1/f noise,
averaging has no effect at all. That´s why 1/f noise is so critical.

One large reason for going from the current "DC" scheme to an "AC"
scheme is that 1/f noise falls off at higher frequencies.

The classic scheme would be some kind of torsionally vibrating coil feeding
an AC coupled amplifier and a synchronous detector. This approach has already
been mentioned and dismissed as being too complex for teaching, but has the
advantage of being workable in exactly such a lab..

It occurs to me that a possible arrangement is two torsionally oscillating
coils that are coaxial and almost touch, but vibrate opposite to one another.
The coils would be wired such that the desired electron acceleration signals
would add, while variation due to changes in coil radial size due to
centrifugal effect interacting with the local magnetic field would largely
cancel.

..

PMI's old designs used SiN passivation with SiO2 overcoat, and had
very low 1/f noise; those OP27s, and other offerings, are available from
AD nowadays. 80nV in 0.1 to 10 Hz bandwidth, and you only really
care about 0.1 to 1 Hz if you look at the brake-pulse integration. It might
hurt the take-a-thousand-readings schemes, however.

Lower 1/f noise is always helpful.

Joe Gwinn

 

[Carl]

"Joseph Gwinn" wrote in message
news:0001HW.22AB175D0056A5727000016402EF@news.giganews.com...

While we may not be able to put a battery in the rotating coil, it occurs
to
me that we could put a zero-bias JFET preamp in the coil, power from
outside
via a twisted pair that also carries the amplified signal. Feed from a
constant voltage source and sense the current draft. This way, capacitance
in
the twisted pair has little effect. And the twisted pair cancels magnetic
fields from powering the JFET.

It's Friday and I'm bored waiting for my pizza to arrive - Why not put a
ring of solar cells around the center of the disc that supports the coil,
with a ring of stationary high intensity LED's above them, to power the coil
and on-board preamp, and then put an LED on the axis with a photodiode above
it to get the signal out. No moving contacts, no long leads. Put the solar
cells on the bottom and the output LED on the top of the disc to minimize
any crosstalk.

--
Regards,
Carl Ijames

 

[John Larkin]

On Fri, 7 Jun 2019 19:41:40 -0400, "Carl"
<carl.ijamesXYZ@ZYXverizon.net> wrote:

"Joseph Gwinn" wrote in message
news:0001HW.22AB175D0056A5727000016402EF@news.giganews.com...
While we may not be able to put a battery in the rotating coil, it occurs
to
me that we could put a zero-bias JFET preamp in the coil, power from
outside
via a twisted pair that also carries the amplified signal. Feed from a
constant voltage source and sense the current draft. This way, capacitance
in
the twisted pair has little effect. And the twisted pair cancels magnetic
fields from powering the JFET.

It's Friday and I'm bored waiting for my pizza to arrive - Why not put a
ring of solar cells around the center of the disc that supports the coil,
with a ring of stationary high intensity LED's above them, to power the coil
and on-board preamp, and then put an LED on the axis with a photodiode above
it to get the signal out. No moving contacts, no long leads. Put the solar
cells on the bottom and the output LED on the top of the disc to minimize
any crosstalk.

I was thinking of using a supercap to power a diffamp. If the
amplified signal comes off the spinning coil via a pair of slip rings
or equivalent, the same pair of wires could be used to charge the
supercap, probably through the ESD diodes of the diffamp.

A non-contact way to get the signal off would be great, but requires a
lot more parts.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[whit3rd]

On Friday, June 7, 2019 at 2:52:34 PM UTC-7, Joseph Gwinn wrote:

On Jun 7, 2019, whit3rd wrote
(in article<f4eb199d-086c-4be0-8fe2-8dc37a36ab7e@googlegroups.com&gt:

On Friday, June 7, 2019 at 8:55:17 AM UTC-7, George Herold wrote:

And no one's mentioned 1/f noise.

Noise only makes a single run uncertain, multiple runs will solve that.

For gaussian noise and the like, averaging does help. For 1/f noise,
averaging has no effect at all. That´s why 1/f noise is so critical.

In what context? If you null the capacitor charge, then do a few-seconds experiment,
there's both a lower and upper frequency limit to the whole experiment.

Then you can repeat the experiment a few dozen times, and expect a gaussian
distribution. Nothing about the 'DC' experiment involves day-long
durations which would build up noise. The deceleration/active sensing
is a few tenths of a second only.

 

[whit3rd]

On Friday, June 7, 2019 at 2:40:00 PM UTC-7, John Larkin wrote:

On Fri, 7 Jun 2019 14:22:06 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

Now you aren't thinking like a scientist. 'Something is wrong' means you can test
a new hypothesis, but it doesn't tell you WHAT new hypothesis. There's no value
in a 'something is wrong' determination unless another hypothesis can be put forward.

I wouldn't submit a paper, or teach a class, if the phenom involved is
an artifact.

Every phenomenon IS an artifact, that's what we're looking for.

Seeing the coil voltage would be useful in understanding what's going
on. Hiding it as a single integrated number is keeping your head in
the sand.

No, it's making a controlled experiment with minimal noise sensitivity.
It's experiment design. The design goal is to produce signal, not noise.

Testing for 'unknown' is less than productive,
and demonstrates... nothing in particular.

Isn't that what science does, discover things?

Exploration which is part of a plan, does discover things. You have no plan, except
to find noise (or pickup from anbient sources beyond the scope of the investigation).

You aren't welcome in my lab!

Do you have a lab? Do you have an oscilloscope?

A place where one controls the circumstances, IS a lab. Every kitchen, for instance. Or darkroom.
Yeah, a few oscilloscopes. Neither is relevant information for any known purpose
you might have, though. Those are the wrong questions to ask.

What IS relevant, is knowledge-seeking behavior (science); finding ways (experiments) to
build data to support a conclusion. Effective q/m ratio for charge carriers in metals,
is a quantity to be measured, and the apparatus is a way to do that. Digitizing everything
you can, is a fit to your business model, but serves no other purpose.

You pointed to a website with some guy painting boxes differently and collecting data, then
talking about all the wiggles he saw. He won't ever reach a conclusion that way, he has NO
HYPOTHESIS TO TEST, and all the data in the world won't give him a clue. He also has
no theory of his 'noise', nor seems likely ever to generate one. Inconclusive work is... a
waste of time. The boxes looked pretty, in the sunlight, though.

 

[Jan Panteltje]

On a sunny day (Fri, 7 Jun 2019 11:43:20 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
<2baf4734-268d-4eaf-8abf-e8a592428605@googlegroups.com>:

On Friday, June 7, 2019 at 9:53:00 AM UTC-4, John Larkin wrote:
On Fri, 07 Jun 2019 13:13:11 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Fri, 7 Jun 2019 03:59:16 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
85e803ec-c2d7-4b6a-a752-ce08625c0a32@googlegroups.com>:

Jan Panteltje, several kOhm of input impedance will reduce our expected current
by a factor of ten or more. So I am not sure your design will work. We'd
drop our expected current down to 100 pA, or less.

This is the interesting part.
That 100 pA (1e-10) will flow into the base junction of that transistor and if it is a high beta type
here for the simplicity of numbers not hFE 900 but 1000, result in a collector current of 1e-7,
or .1 uA.
In a 10 MOhm collector resistor that will give 1 V (1e-7 * 1e7).

There seems to be a basic misunderstanding about how opamps work,

And some basic misunderstandings of how transistors work. Higher beta
does not increase the voltage gain of the usual transistor amplifier.

200 nV will not push 100 pA into the base of a transistor whose
collector current is around 1 uA. The impedance looking into the base
will be 10s of megohms.

I'm not sure how to calculate the input impedance..
(I know, look in AoE.)
But isn't the problem the emitter resistance. r_e = 25 mV/Ic
At 1 uA of Ic, r_e = 25 k ohm and the gain is R_c/ r_e = 400.

Jan, Do you know the Ebers-Moll model of the transistor?

Yes

George H.

 

[Jan Panteltje]

On a sunny day (Fri, 07 Jun 2019 16:47:59 -0700) it happened John Larkin
<jjlarkin@highland_snip_technology.com> wrote in
<gmtlfepv8gamvmfbsl7g09qsmhj3dq822h@4ax.com>:

On Fri, 7 Jun 2019 19:41:40 -0400, "Carl"
carl.ijamesXYZ@ZYXverizon.net> wrote:

"Joseph Gwinn" wrote in message
news:0001HW.22AB175D0056A5727000016402EF@news.giganews.com...
While we may not be able to put a battery in the rotating coil, it occurs
to
me that we could put a zero-bias JFET preamp in the coil, power from
outside
via a twisted pair that also carries the amplified signal. Feed from a
constant voltage source and sense the current draft. This way, capacitance
in
the twisted pair has little effect. And the twisted pair cancels magnetic
fields from powering the JFET.

It's Friday and I'm bored waiting for my pizza to arrive - Why not put a
ring of solar cells around the center of the disc that supports the coil,
with a ring of stationary high intensity LED's above them, to power the coil
and on-board preamp, and then put an LED on the axis with a photodiode above
it to get the signal out. No moving contacts, no long leads. Put the solar
cells on the bottom and the output LED on the top of the disc to minimize
any crosstalk.

I was thinking of using a supercap to power a diffamp. If the
amplified signal comes off the spinning coil via a pair of slip rings
or equivalent, the same pair of wires could be used to charge the
supercap, probably through the ESD diodes of the diffamp.

A non-contact way to get the signal off would be great, but requires a
lot more parts.

1 laser diode in center disc shining up?

= photo doide receiver

^ laser diode with simple drive electronicspowered by lithium cell
======== disk
=== bearing
[ | ] break
=== bearing
|
[ ] spring or rubber band driving mechanism, no electric motors and fields
| \0 /
deserted island O experimenter \/ \/drinks O hula girls
///////////////////////////////////////////////////////////////////////////////

 

[Jan Panteltje]

On a sunny day (Fri, 07 Jun 2019 12:08:56 -0700) it happened John Larkin
<jjlarkin@highland_snip_technology.com> wrote in
<t7clfedaenjnauhrbb9ksd0so2gqajho51@4ax.com>:

What spice?

LT Spice. It's free and fairly easy to learn and use. It includes a
lot of transistor and mosfet and diode models.

I rarely do much of the old classic EE math any more... just guess
then Spice it. I even Spice voltage dividers and RC timers and such.

I just did an RLC to go between an opamp and a 40 Ms/s ADC input. The
ADC data sheet wants an RC, but the time constant was too slow for my
purposes. A little inductance snaps it right up.

And I had another case: we're redesigning a laser controller, for IC
lithography, that we did in 2002. We used (at the customer's request)
a Maxim tapped silicon delay line to generate some asynchronous
delays. The part is naturally long gone, so I'll use a triggered
oscillator and some FPGA logic to do the same function.

This took minutes to simulate:

https://www.dropbox.com/s/nezshpka0eush92/Tplus_Trig_Osc_2.jpg?dl=0

Very nice.
Yes I have LTspice,
it runs OK on an other PC, on this one it crashes the system,
probably a Linux windows emulator 'wine' fault.
It sometimes makes predictions that are not reality,
it predicted a video amplifier I designed would oscillate,
ten boards made and no oscillations...

Nice for filters and stuff that take a lot of time to calculate by hand.
There are also special filter programs though.


As to 'what spice' I was sort of joking a bit, my apologies,
French fries too much mayonnaise, should not have eaten almost the whole jar...


I may have a go at building that circuit I proposed,
and use a 10M 10x scope probe as collector resistor.
If it turns out the Ic is already too high at room temperature,
then I am wrong.
Maybe be after the weekend, some other project coming up now, garden fence repair..
We had oops (garden chair flies, goes outside stores stuff),
HAVE bad storms here.

 

[amdx]

On 6/4/2019 4:48 PM, Joerg wrote:

On 2019-06-04 13:46, George Herold wrote:

I have no idea about any of this, but wonder if a rotary transformer
is of any use, and my source would be from a VCR, always thought they
were a bit magical.
Mikek
PS, not sure it won't blow apart stopping 1/2 second.

 

[John Larkin]

On Sat, 08 Jun 2019 06:59:37 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Fri, 07 Jun 2019 12:08:56 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
t7clfedaenjnauhrbb9ksd0so2gqajho51@4ax.com>:

What spice?

LT Spice. It's free and fairly easy to learn and use. It includes a
lot of transistor and mosfet and diode models.

I rarely do much of the old classic EE math any more... just guess
then Spice it. I even Spice voltage dividers and RC timers and such.

I just did an RLC to go between an opamp and a 40 Ms/s ADC input. The
ADC data sheet wants an RC, but the time constant was too slow for my
purposes. A little inductance snaps it right up.

And I had another case: we're redesigning a laser controller, for IC
lithography, that we did in 2002. We used (at the customer's request)
a Maxim tapped silicon delay line to generate some asynchronous
delays. The part is naturally long gone, so I'll use a triggered
oscillator and some FPGA logic to do the same function.

This took minutes to simulate:

https://www.dropbox.com/s/nezshpka0eush92/Tplus_Trig_Osc_2.jpg?dl=0

Very nice.
Yes I have LTspice,
it runs OK on an other PC, on this one it crashes the system,
probably a Linux windows emulator 'wine' fault.
It sometimes makes predictions that are not reality,
it predicted a video amplifier I designed would oscillate,
ten boards made and no oscillations...

Nice for filters and stuff that take a lot of time to calculate by hand.
There are also special filter programs though.


As to 'what spice' I was sort of joking a bit, my apologies,
French fries too much mayonnaise, should not have eaten almost the whole jar...

The world divides in to people who love mayonnaise (me and The Brat)
and people who are repulsed by it (her sister and my wife.)

When I'm using it I hide the jar behind the toaster so Mo isn't
grossed out.

I may have a go at building that circuit I proposed,
and use a 10M 10x scope probe as collector resistor.
If it turns out the Ic is already too high at room temperature,
then I am wrong.

It's hard to get high voltage gain from a single transistor with a
resistive collector load. As the resistor goes up, you have to reduce
Ic, so that reduces Ib, and Zin goes up, so there less input signal
current, etc. A current source helps some.

I think the idealized transistor amplifier has a voltage gain that is
40 times the DC voltage drop in the collector resistor, something like
that.

Maybe be after the weekend, some other project coming up now, garden fence repair..
We had oops (garden chair flies, goes outside stores stuff),
HAVE bad storms here.

We had wonderful storms in New Orleans, but the weather in San
Francisco is lame. We don't even get lightning. June 8, 2019, 7AM, the
temperature is 58F.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Joerg]

On 2019-06-08 07:16, Joerg wrote:

On 2019-06-08 07:02, John Larkin wrote:
On Tue, 04 Jun 2019 14:48:36 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-06-04 13:46, George Herold wrote:
On Tuesday, June 4, 2019 at 3:28:55 PM UTC-4, ithacacoll...@gmail.com
wrote:
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’d 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’d like to get rid of that noise. In
particular, it is really good at finding 60 Hz signals in the
room.

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. 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

Hi Matt, Thanks for asking here... I guess I'm hoping that this will
give you more ideas, than just you and I going back and forth on
email.

The OPA140 looks fine. 1G ohm and 10 pF is a 10 ms time constant..

But your big problem is the 60 Hz pickup from your coil?

How big is your coil (diameter)? Do you see signals from the coil
spinning in the earth's B-field? I was browsing this,
https://authors.library.caltech.edu/3372/1/TOLpr16b.pdf (from your
wiki link) and it looks to be a big coil. But hard to tell.

We do a trick in our Earth's field nmr where there are two coils in
series (but wound in opposite directions.) A many turn inner coil
that picks up the nmr signal. and a much bigger outer coil, with the
same turns*area as the inner coil. And this picks up the same emf
from the AC 60 Hz as the signal coil... and cancels it. I think JR
will take a turn or two off the inner coil to try and match the
cancellation.


If the 60Hz getting in is E-field there is also the trick of winding
with coax and grounding one side (and only one).

However, much of it will be magnetic and then Matt can only notch it
out. If the detection is done in software notch filters are easy. If
analog you'd almost have to use a switched-capacitor filter for that.
Very likely several notch filters are required because when 60Hz is gone
Matt will discover that there's also a lot of 180Hz and 300Hz. Also,
make sure there is absolutely no 60Hz gear that turns on and off at
randon, such as electric cooktops, because that's next to impossible to
notch out.

A serious lowpass filter would take all the HF stuff out; his signal
is ballpark 1 Hz.


I might have misunderstood, I though he needs to observe a sharp end of
some otherwise slow electron effect. If you need only a few Hz BW, yes,
then lowpass is the ticket.


... But that won't work if anything rails ahead of the
filter.


At 1e9 current-to-voltage transfer ratio I am afraid that can happen
easily. Worst case in spurts and that really messes up any signal.

Old rule in RF engineering: Make the gain in the first stage only as
high as needed to overcome non-man-made noise. Follow with filtering
immediately, and only then amplify more.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 2019-06-08 07:02, John Larkin wrote:

On Tue, 04 Jun 2019 14:48:36 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-06-04 13:46, George Herold wrote:
On Tuesday, June 4, 2019 at 3:28:55 PM UTC-4, ithacacoll...@gmail.com
wrote:
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’d 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’d like to get rid of that noise. In
particular, it is really good at finding 60 Hz signals in the
room.

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. 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

Hi Matt, Thanks for asking here... I guess I'm hoping that this will
give you more ideas, than just you and I going back and forth on
email.

The OPA140 looks fine. 1G ohm and 10 pF is a 10 ms time constant..

But your big problem is the 60 Hz pickup from your coil?

How big is your coil (diameter)? Do you see signals from the coil
spinning in the earth's B-field? I was browsing this,
https://authors.library.caltech.edu/3372/1/TOLpr16b.pdf (from your
wiki link) and it looks to be a big coil. But hard to tell.

We do a trick in our Earth's field nmr where there are two coils in
series (but wound in opposite directions.) A many turn inner coil
that picks up the nmr signal. and a much bigger outer coil, with the
same turns*area as the inner coil. And this picks up the same emf
from the AC 60 Hz as the signal coil... and cancels it. I think JR
will take a turn or two off the inner coil to try and match the
cancellation.


If the 60Hz getting in is E-field there is also the trick of winding
with coax and grounding one side (and only one).

However, much of it will be magnetic and then Matt can only notch it
out. If the detection is done in software notch filters are easy. If
analog you'd almost have to use a switched-capacitor filter for that.
Very likely several notch filters are required because when 60Hz is gone
Matt will discover that there's also a lot of 180Hz and 300Hz. Also,
make sure there is absolutely no 60Hz gear that turns on and off at
randon, such as electric cooktops, because that's next to impossible to
notch out.

A serious lowpass filter would take all the HF stuff out; his signal
is ballpark 1 Hz.

I might have misunderstood, I though he needs to observe a sharp end of
some otherwise slow electron effect. If you need only a few Hz BW, yes,
then lowpass is the ticket.

... But that won't work if anything rails ahead of the
filter.

At 1e9 current-to-voltage transfer ratio I am afraid that can happen
easily. Worst case in spurts and that really messes up any signal.

--
Regards, Joerg

http://www.analogconsultants.com/

 

Hi all,

I lot of people are suggested putting the measurement circuit directly on the rotating coil, which is an interesting idea, but has me worried on a couple counts. First, the coil is very heavy (2 kg) and spins very quickly (6000 rpm), and all the mass is at the edges of the disk (20 cm in diameter) so balancing that is critical.

Second, the large coils are very sensitive magnetic field detectors (unfortunately -- that's my whole problem!). So I am worried as the current flows in the circuit on the coil I will measure that current and create some sort of unintended infinite feedback.

We used to have the speed sensor on the shaft below the coils. It was down about 10 cm below the coils. It is a little photodiode and laser that senses an alternating black and white strip of paper. But as the current turns on and off in the photodiode, I could see that signal in the coil clear as day. We had to move the motor and speed sensor 1 m away from the coils to make it go away. So, I am worried that even a small current right on top of the coil will create enough magnetic field for my coil to pick it up.

 

[John Larkin]

On Sat, 08 Jun 2019 06:59:37 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Fri, 07 Jun 2019 16:47:59 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
gmtlfepv8gamvmfbsl7g09qsmhj3dq822h@4ax.com>:

On Fri, 7 Jun 2019 19:41:40 -0400, "Carl"
carl.ijamesXYZ@ZYXverizon.net> wrote:

"Joseph Gwinn" wrote in message
news:0001HW.22AB175D0056A5727000016402EF@news.giganews.com...
While we may not be able to put a battery in the rotating coil, it occurs
to
me that we could put a zero-bias JFET preamp in the coil, power from
outside
via a twisted pair that also carries the amplified signal. Feed from a
constant voltage source and sense the current draft. This way, capacitance
in
the twisted pair has little effect. And the twisted pair cancels magnetic
fields from powering the JFET.

It's Friday and I'm bored waiting for my pizza to arrive - Why not put a
ring of solar cells around the center of the disc that supports the coil,
with a ring of stationary high intensity LED's above them, to power the coil
and on-board preamp, and then put an LED on the axis with a photodiode above
it to get the signal out. No moving contacts, no long leads. Put the solar
cells on the bottom and the output LED on the top of the disc to minimize
any crosstalk.

I was thinking of using a supercap to power a diffamp. If the
amplified signal comes off the spinning coil via a pair of slip rings
or equivalent, the same pair of wires could be used to charge the
supercap, probably through the ESD diodes of the diffamp.

A non-contact way to get the signal off would be great, but requires a
lot more parts.

1 laser diode in center disc shining up?

= photo doide receiver

^ laser diode with simple drive electronicspowered by lithium cell
======== disk
=== bearing
[ | ] break
=== bearing
|
[ ] spring or rubber band driving mechanism, no electric motors and fields
| \0 /
deserted island O experimenter \/ \/drinks O hula girls
///////////////////////////////////////////////////////////////////////////////

Are you proposing that we instrument the angular rotation of hula
girls? That might require an extended series of field experiments.

I once left a woman in a volcano crater on Maui. We weren't getting
along.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Tue, 04 Jun 2019 14:48:36 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2019-06-04 13:46, George Herold wrote:
On Tuesday, June 4, 2019 at 3:28:55 PM UTC-4, ithacacoll...@gmail.com
wrote:
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’d 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’d like to get rid of that noise. In
particular, it is really good at finding 60 Hz signals in the
room.

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. 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

Hi Matt, Thanks for asking here... I guess I'm hoping that this will
give you more ideas, than just you and I going back and forth on
email.

The OPA140 looks fine. 1G ohm and 10 pF is a 10 ms time constant..

But your big problem is the 60 Hz pickup from your coil?

How big is your coil (diameter)? Do you see signals from the coil
spinning in the earth's B-field? I was browsing this,
https://authors.library.caltech.edu/3372/1/TOLpr16b.pdf (from your
wiki link) and it looks to be a big coil. But hard to tell.

We do a trick in our Earth's field nmr where there are two coils in
series (but wound in opposite directions.) A many turn inner coil
that picks up the nmr signal. and a much bigger outer coil, with the
same turns*area as the inner coil. And this picks up the same emf
from the AC 60 Hz as the signal coil... and cancels it. I think JR
will take a turn or two off the inner coil to try and match the
cancellation.


If the 60Hz getting in is E-field there is also the trick of winding
with coax and grounding one side (and only one).

However, much of it will be magnetic and then Matt can only notch it
out. If the detection is done in software notch filters are easy. If
analog you'd almost have to use a switched-capacitor filter for that.
Very likely several notch filters are required because when 60Hz is gone
Matt will discover that there's also a lot of 180Hz and 300Hz. Also,
make sure there is absolutely no 60Hz gear that turns on and off at
randon, such as electric cooktops, because that's next to impossible to
notch out.

A serious lowpass filter would take all the HF stuff out; his signal
is ballpark 1 Hz. But that won't work if anything rails ahead of the
filter.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Sat, 8 Jun 2019 09:58:26 -0500, amdx <nojunk@knology.net> wrote:

On 6/8/2019 9:02 AM, John Larkin wrote:
On Tue, 04 Jun 2019 14:48:36 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-06-04 13:46, George Herold wrote:
On Tuesday, June 4, 2019 at 3:28:55 PM UTC-4, ithacacoll...@gmail.com
wrote:
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’d 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’d like to get rid of that noise. In
particular, it is really good at finding 60 Hz signals in the
room.

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. 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

Hi Matt, Thanks for asking here... I guess I'm hoping that this will
give you more ideas, than just you and I going back and forth on
email.

The OPA140 looks fine. 1G ohm and 10 pF is a 10 ms time constant..

But your big problem is the 60 Hz pickup from your coil?

How big is your coil (diameter)? Do you see signals from the coil
spinning in the earth's B-field? I was browsing this,
https://authors.library.caltech.edu/3372/1/TOLpr16b.pdf (from your
wiki link) and it looks to be a big coil. But hard to tell.

We do a trick in our Earth's field nmr where there are two coils in
series (but wound in opposite directions.) A many turn inner coil
that picks up the nmr signal. and a much bigger outer coil, with the
same turns*area as the inner coil. And this picks up the same emf
from the AC 60 Hz as the signal coil... and cancels it. I think JR
will take a turn or two off the inner coil to try and match the
cancellation.


If the 60Hz getting in is E-field there is also the trick of winding
with coax and grounding one side (and only one).

However, much of it will be magnetic and then Matt can only notch it
out. If the detection is done in software notch filters are easy. If
analog you'd almost have to use a switched-capacitor filter for that.
Very likely several notch filters are required because when 60Hz is gone
Matt will discover that there's also a lot of 180Hz and 300Hz. Also,
make sure there is absolutely no 60Hz gear that turns on and off at
randon, such as electric cooktops, because that's next to impossible to
notch out.

A serious lowpass filter would take all the HF stuff out; his signal
is ballpark 1 Hz. But that won't work if anything rails ahead of the
filter.


You didn't directly respond to me, but I'm afraid a VCR rotary
transformer is more of a high pass filter and wouldn't be much use at 1 HZ.
Mikek

A magnetic or optical coupler would probably need some sort of
modulation, which would be a lot of electronics to spin.

One could use mag coupling into the stationary coil which is already
there. Then there would only be one signal to digitize.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Joseph Gwinn]

On Jun 8, 2019, whit3rd wrote
(in article<b8c14aeb-17f6-44c7-b629-4853d6c665a2@googlegroups.com&gt:

On Friday, June 7, 2019 at 2:52:34 PM UTC-7, Joseph Gwinn wrote:
On Jun 7, 2019, whit3rd wrote
(in article<f4eb199d-086c-4be0-8fe2-8dc37a36ab7e@googlegroups.com&gt:

On Friday, June 7, 2019 at 8:55:17 AM UTC-7, George Herold wrote:

And no one's mentioned 1/f noise.

Noise only makes a single run uncertain, multiple runs will solve that.

For gaussian noise and the like, averaging does help. For 1/f noise,
averaging has no effect at all. That´s why 1/f noise is so critical.

In what context? If you null the capacitor charge, then do a few-seconds
experiment,
there's both a lower and upper frequency limit to the whole experiment.

This is cancellation, not averaging.

There are lots of schemes to cancel 1/f noise (called _drift_ when the f is
low enough), and taking two samples close in time, one with the other without
the sought data, and differencing is the foundation.

Here is the grand-daddy of such schemes:

..<https://en.wikipedia.org/wiki/Microwave_radiometer>

It is also the ancestor of lock-in amplifiers in general. Dicke founded
Princeton Applied Research to commercialize the invention.

..<https://en.wikipedia.org/wiki/Lock-in_amplifier>

..
Which brings me to a thought: If the signal of interest is a few Hertz, and
drifts et al are a big deal, this may be a perfect application for a
chopper-stabilized amplifier of some sort.

..

Then you can repeat the experiment a few dozen times, and expect a gaussian
distribution. Nothing about the 'DC' experiment involves day-long
durations which would build up noise. The deceleration/active sensing
is a few tenths of a second only.

Not quite. There is always some residual 1/f component, and this component
does not average away, and so will come to dominate. So one always has to
reduce the 1/f level.

Joe Gwinn

 

[Jan Panteltje]

On a sunny day (Sat, 8 Jun 2019 07:10:39 -0700 (PDT)) it happened
ithacacollegephysics@gmail.com wrote in
<326636f8-2b6c-465b-a939-561a584cf4b6@googlegroups.com>:
So, I am worried that even a small current right on top
>of the coil will create enough magnetic field for my coil to pick it up.

Circuit in mu-metal box?

 

[Jan Panteltje]

On a sunny day (Sat, 08 Jun 2019 07:08:12 -0700) it happened John Larkin
<jjlarkin@highlandtechnology.com> wrote in
<a5gnfelsbbsa0b1au9mh0uca0dtrm09i9o@4ax.com>:

On Sat, 08 Jun 2019 06:59:37 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Fri, 07 Jun 2019 16:47:59 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
gmtlfepv8gamvmfbsl7g09qsmhj3dq822h@4ax.com>:

On Fri, 7 Jun 2019 19:41:40 -0400, "Carl"
carl.ijamesXYZ@ZYXverizon.net> wrote:

"Joseph Gwinn" wrote in message
news:0001HW.22AB175D0056A5727000016402EF@news.giganews.com...
While we may not be able to put a battery in the rotating coil, it occurs
to
me that we could put a zero-bias JFET preamp in the coil, power from
outside
via a twisted pair that also carries the amplified signal. Feed from a
constant voltage source and sense the current draft. This way, capacitance
in
the twisted pair has little effect. And the twisted pair cancels magnetic
fields from powering the JFET.

It's Friday and I'm bored waiting for my pizza to arrive - Why not put a
ring of solar cells around the center of the disc that supports the coil,
with a ring of stationary high intensity LED's above them, to power the coil
and on-board preamp, and then put an LED on the axis with a photodiode above
it to get the signal out. No moving contacts, no long leads. Put the solar
cells on the bottom and the output LED on the top of the disc to minimize
any crosstalk.

I was thinking of using a supercap to power a diffamp. If the
amplified signal comes off the spinning coil via a pair of slip rings
or equivalent, the same pair of wires could be used to charge the
supercap, probably through the ESD diodes of the diffamp.

A non-contact way to get the signal off would be great, but requires a
lot more parts.

1 laser diode in center disc shining up?

= photo doide receiver

^ laser diode with simple drive electronicspowered by lithium cell
======== disk
=== bearing
[ | ] break
=== bearing
|
[ ] spring or rubber band driving mechanism, no electric motors and fields
| \0 /
deserted island O experimenter \/ \/drinks O hula girls
///////////////////////////////////////////////////////////////////////////////


Are you proposing that we instrument the angular rotation of hula
girls? That might require an extended series of field experiments.

I once left a woman in a volcano crater on Maui. We weren't getting
along.

Oops, she still there?

Now this..
Take a 74HC4046, center frequency 27 MHz, sweep 1 - 50 MHz for 1 to 5 V makes 10 MHz per volt.
take the 200 nV, and put it into VCO in,
this cause a frequency shift of 2e-7 * 1e7 = 2 Hz.
Small antenna on output 4046.

Tune to 27 MHz with my CB narrow band FM receiver.
Has about +- 5 kHz for 1Vpp out to headphone jack?

So 2 / 5000 volt .4 mV....

Maybe you can already hear that! -46dB

If you add the TIA or something with a gain of 100 at the TX side.
then you get 40 mV....
Clipping is no problem...

This also solves the 'how do I get the signal out' problem.
Somehow I think HC4046 can be configured more sensitive?
Need to read up on the datasheet and what I did in the past with it,
whole lot of those chips in projects.

The CB set runs on battery, no mains needed.
It has, on NBFM, very good SNR.

Would also work with my Tecsun PL600 PLL shortwave receiver, pick any frequency not in use.

 

[amdx]

On 6/8/2019 9:02 AM, John Larkin wrote:

On Tue, 04 Jun 2019 14:48:36 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-06-04 13:46, George Herold wrote:
On Tuesday, June 4, 2019 at 3:28:55 PM UTC-4, ithacacoll...@gmail.com
wrote:
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’d 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’d like to get rid of that noise. In
particular, it is really good at finding 60 Hz signals in the
room.

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. 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

Hi Matt, Thanks for asking here... I guess I'm hoping that this will
give you more ideas, than just you and I going back and forth on
email.

The OPA140 looks fine. 1G ohm and 10 pF is a 10 ms time constant..

But your big problem is the 60 Hz pickup from your coil?

How big is your coil (diameter)? Do you see signals from the coil
spinning in the earth's B-field? I was browsing this,
https://authors.library.caltech.edu/3372/1/TOLpr16b.pdf (from your
wiki link) and it looks to be a big coil. But hard to tell.

We do a trick in our Earth's field nmr where there are two coils in
series (but wound in opposite directions.) A many turn inner coil
that picks up the nmr signal. and a much bigger outer coil, with the
same turns*area as the inner coil. And this picks up the same emf
from the AC 60 Hz as the signal coil... and cancels it. I think JR
will take a turn or two off the inner coil to try and match the
cancellation.


If the 60Hz getting in is E-field there is also the trick of winding
with coax and grounding one side (and only one).

However, much of it will be magnetic and then Matt can only notch it
out. If the detection is done in software notch filters are easy. If
analog you'd almost have to use a switched-capacitor filter for that.
Very likely several notch filters are required because when 60Hz is gone
Matt will discover that there's also a lot of 180Hz and 300Hz. Also,
make sure there is absolutely no 60Hz gear that turns on and off at
randon, such as electric cooktops, because that's next to impossible to
notch out.

A serious lowpass filter would take all the HF stuff out; his signal
is ballpark 1 Hz. But that won't work if anything rails ahead of the
filter.

You didn't directly respond to me, but I'm afraid a VCR rotary
transformer is more of a high pass filter and wouldn't be much use at 1 HZ.
Mikek