Re: [volt-nuts] Bohnenberger electrometer

2018-03-16 Thread Neville Michie
In the lexicon of physical devices is an item called an electret.
Commercially these are used in capacitive microphones.
The common ones consist of polymer sheet that has been annealed in a voltage 
gradient.
An accidental example is the swarf from methyl methacrylate (Perspex, 
Plexiglass) which will stick
permanently to surfaces when it is turned in a lathe.
I should think that the materials like barium titanate could be used to make 
electrets.
A polymer film electret in a leaf electroscope would make a polarity sensitive 
instrument.
BTW some mineral crystals eg tourmaline are pyroelectric, when heated they 
become charged on
oposite faces forming an electret.

cheers, Neville Michie

> On 16 Mar 2018, at 23:52, Dr. David Kirkby  
> wrote:
> 
> On 6 March 2018 at 09:40, Dr. David Kirkby 
> wrote:
> 
>> Sorry this is not precision voltage measurement, but it is not unrelated.
>> 
>> As a radio club project, we are building a simple electroscope, with no
>> active components. The gold leave variety would work, but two bits of
>> alluminum foil do too.
>> 
>> My plan was to go one better, and build a Bohnenberger electrometer.
>> 
> 
> For what it is worth, this is my design:
> 
> http://www.kirkbymicrowave.co.uk/tmp/G8WRBs-electrometer.jpg
> 
> There's 600 V DC between two strips of PCB material. A 600 V 47 uF
> capacitor was charged to 600 V. A small bit of aluminum foil, between the
> plates, then moves to the left or right, depending on whether the charge is
> positive or negative. The big capacitor, which is 2.2 nF 15 kV is not doing
> much apart from being a structure to hold other parts. It has large lugs on
> it, where multiple M6 screws can be fitted, so it is nice electrical
> insulator. Its actual capacitance (2.2 nF) is insignificant when in
> parallel with 47 uF.
> 
> Under sufficient applied field, and with sufficient charge, it is possible
> to get the foil to oscillate from side to side like a pendulum. I believe
> what happens is if a negative charge is applied to the foil, it gets
> attracted to the positive plate, which causes them to touch, so the foil
> receives a positive charge - the opposite of what it had before. This
> causes it to move in the other direction. It is possible to get it to
> oscillate back and forth. I expect, with a sufficient mass and very high
> electric field, a pendulum could be made to make a clock, but with a little
> bit of tin foil, the foil would clearly break quite quickly. A more
> substantial structure would be required, which I suspect would need some
> very high voltages.
> 
> A Google of 'electrostatic clocks' does indicate they exist, although I
> have not looked into how they work. But I believe a sufficiently high
> electric field could make a pendulum swing, and that of course could make a
> clock.
> 
> Anyway, it was interesting playing with this.
> 
> I am wondering if there's any way to detect the polarity of a charge,
> without having any power source. Clearly the gold leaf electroscope can
> detect charge, but does not need a power supply. The Bohnenberger
> electrometer can detect polarity too, but needs a power supply. I was
> wondering if the charge could be applied to two diodes, which were each
> connected to a plate. The it may be possible to charge one plate only, as
> only one diode would conduct, so only one plate would be charged. The the
> leaf would be repelled from whatever plate has the same charge.
> 
> Dave
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Re: [volt-nuts] Bohnenberger electrometer

2018-03-16 Thread Bruce Griffiths
A method in use 40+ odd years ago for measuring atmospheric electric fields was 
to use a slotted rotating disk rather than the rotating cylinder.

A matching stationary or counter rotating disk IIRC was used either in front or 
behind the rotating slotted disk the the sensing disk was behind both.

Bruce.


> 
> On 17 March 2018 at 07:53 ed breya  wrote:
> 
> There is another kind of static electric field meter that was commonly
> used over the past few decades for monitoring charges/voltages in work
> areas dealing with sensitive semiconductors. It has a small motor
> spinning a hollow brass cylinder that has a radial hole or slot that
> alternately shields and exposes a center cylinder inside, which is the
> pickup electrode. This action causes a small AC signal on the electrode,
> that can be amplified up to represent the electric field strength from
> any nearby object. The signal is then rectified and trips a comparator
> and LED indicator if the level exceeds a certain amount.
> 
> I have a couple of these units, but have never experimented with them
> yet. They don't show any kind of readout or provide a measuring signal -
> just the LED warning of excessive (unknown trip point) static charge
> nearby. I figured someday I would modify one up and add a signal output
> port and a sync output from the motor, allowing a lock-in analyzer to
> read the result over a wide range, and maybe even be fairly accurate or
> calibrate-able.
> 
> Ed
> 
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Re: [volt-nuts] Bohnenberger electrometer

2018-03-16 Thread ed breya
Yes Hendrik, same principle as the butterfly disk style, but mine use 
cylinders - the field exposure is radial instead of axial.  Ed


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Re: [volt-nuts] Bohnenberger electrometer

2018-03-16 Thread Hendrik

Something like this ? https://de.wikipedia.org/wiki/Elektrofeldmeter

(German wikipedia as the english entry is less than stellar. They are 
called field mill.)



Best regards

Hendrik



On 16.03.2018 19:53, ed breya wrote:
There is another kind of static electric field meter that was commonly 
used over the past few decades for monitoring charges/voltages in work 
areas dealing with sensitive semiconductors. It has a small motor 
spinning a hollow brass cylinder that has a radial hole or slot that 
alternately shields and exposes a center cylinder inside, which is the 
pickup electrode. This action causes a small AC signal on the 
electrode, that can be amplified up to represent the electric field 
strength from any nearby object. The signal is then rectified and 
trips a comparator and LED indicator if the level exceeds a certain 
amount.


I have a couple of these units, but have never experimented with them 
yet. They don't show any kind of readout or provide a measuring signal 
- just the LED warning of excessive (unknown trip point) static charge 
nearby. I figured someday I would modify one up and add a signal 
output port and a sync output from the motor, allowing a lock-in 
analyzer to read the result over a wide range, and maybe even be 
fairly accurate or calibrate-able.


Ed

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Re: [volt-nuts] Bohnenberger electrometer

2018-03-16 Thread Fred
I once made the alu-foil type but also one with a jfet. The gate as 
"antenna" I have many meters but no static field elctrometer. (and no 
coulomb meter, never seen one in real life too) I like exotic meters. I  
repaired (and modded) a 3 axis fluxgate meter a while back. The owner 
uses it to measure magnetic fields (has to do with installing SEM 
microscopes, he does this all over the world.


Fred PA4TIM


On 03/16/2018 01:52 PM, Dr. David Kirkby wrote:

On 6 March 2018 at 09:40, Dr. David Kirkby 
wrote:


Sorry this is not precision voltage measurement, but it is not unrelated.

As a radio club project, we are building a simple electroscope, with no
active components. The gold leave variety would work, but two bits of
alluminum foil do too.

My plan was to go one better, and build a Bohnenberger electrometer.


For what it is worth, this is my design:

http://www.kirkbymicrowave.co.uk/tmp/G8WRBs-electrometer.jpg

There's 600 V DC between two strips of PCB material. A 600 V 47 uF
capacitor was charged to 600 V. A small bit of aluminum foil, between the
plates, then moves to the left or right, depending on whether the charge is
positive or negative. The big capacitor, which is 2.2 nF 15 kV is not doing
much apart from being a structure to hold other parts. It has large lugs on
it, where multiple M6 screws can be fitted, so it is nice electrical
insulator. Its actual capacitance (2.2 nF) is insignificant when in
parallel with 47 uF.

Under sufficient applied field, and with sufficient charge, it is possible
to get the foil to oscillate from side to side like a pendulum. I believe
what happens is if a negative charge is applied to the foil, it gets
attracted to the positive plate, which causes them to touch, so the foil
receives a positive charge - the opposite of what it had before. This
causes it to move in the other direction. It is possible to get it to
oscillate back and forth. I expect, with a sufficient mass and very high
electric field, a pendulum could be made to make a clock, but with a little
bit of tin foil, the foil would clearly break quite quickly. A more
substantial structure would be required, which I suspect would need some
very high voltages.

A Google of 'electrostatic clocks' does indicate they exist, although I
have not looked into how they work. But I believe a sufficiently high
electric field could make a pendulum swing, and that of course could make a
clock.

Anyway, it was interesting playing with this.

I am wondering if there's any way to detect the polarity of a charge,
without having any power source. Clearly the gold leaf electroscope can
detect charge, but does not need a power supply. The Bohnenberger
electrometer can detect polarity too, but needs a power supply. I was
wondering if the charge could be applied to two diodes, which were each
connected to a plate. The it may be possible to charge one plate only, as
only one diode would conduct, so only one plate would be charged. The the
leaf would be repelled from whatever plate has the same charge.

Dave
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Re: [volt-nuts] Bohnenberger electrometer

2018-03-16 Thread Dr. David Kirkby
On 6 March 2018 at 09:40, Dr. David Kirkby 
wrote:

> Sorry this is not precision voltage measurement, but it is not unrelated.
>
> As a radio club project, we are building a simple electroscope, with no
> active components. The gold leave variety would work, but two bits of
> alluminum foil do too.
>
> My plan was to go one better, and build a Bohnenberger electrometer.
>

For what it is worth, this is my design:

http://www.kirkbymicrowave.co.uk/tmp/G8WRBs-electrometer.jpg

There's 600 V DC between two strips of PCB material. A 600 V 47 uF
capacitor was charged to 600 V. A small bit of aluminum foil, between the
plates, then moves to the left or right, depending on whether the charge is
positive or negative. The big capacitor, which is 2.2 nF 15 kV is not doing
much apart from being a structure to hold other parts. It has large lugs on
it, where multiple M6 screws can be fitted, so it is nice electrical
insulator. Its actual capacitance (2.2 nF) is insignificant when in
parallel with 47 uF.

Under sufficient applied field, and with sufficient charge, it is possible
to get the foil to oscillate from side to side like a pendulum. I believe
what happens is if a negative charge is applied to the foil, it gets
attracted to the positive plate, which causes them to touch, so the foil
receives a positive charge - the opposite of what it had before. This
causes it to move in the other direction. It is possible to get it to
oscillate back and forth. I expect, with a sufficient mass and very high
electric field, a pendulum could be made to make a clock, but with a little
bit of tin foil, the foil would clearly break quite quickly. A more
substantial structure would be required, which I suspect would need some
very high voltages.

A Google of 'electrostatic clocks' does indicate they exist, although I
have not looked into how they work. But I believe a sufficiently high
electric field could make a pendulum swing, and that of course could make a
clock.

Anyway, it was interesting playing with this.

I am wondering if there's any way to detect the polarity of a charge,
without having any power source. Clearly the gold leaf electroscope can
detect charge, but does not need a power supply. The Bohnenberger
electrometer can detect polarity too, but needs a power supply. I was
wondering if the charge could be applied to two diodes, which were each
connected to a plate. The it may be possible to charge one plate only, as
only one diode would conduct, so only one plate would be charged. The the
leaf would be repelled from whatever plate has the same charge.

Dave
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Re: [volt-nuts] Bohnenberger electrometer DANGER

2018-03-08 Thread ed breya
Here's a simplistic view that may be sufficient. Some energy (in the 
form of charge redistribution, which includes current flow) has to come 
from the capacitor, and some from the input signal, to do the work 
needed to push the leaf against gravity. When the input signal is 
removed, some of the energy (charge) stored on the leaf is returned to 
the cap as gravity restores the initial position - roughly the same 
amount of work, depending on leakage and mechanical loss, and heating of 
the protective series resistor.


With a quick review of electrostatics, you could estimate up a simple 
model and the field equations to get a more satisfying, detailed answer. 
It may be more straightforward to look at it from a circuit perspective. 
Picture it as as a very small, non-linear capacitor (the leaf structure) 
in series with a much much larger regular capacitor charged up to a 
constant DC voltage. Any actual series resistance is just resistance, 
and the mechanical loss can be represented as more resistance added in 
series. Presuming the leaf never actually touches or emits particles* or 
arcs to the reference capacitor node, it's basically a capacitive 
voltage divider, and the applied signal may be considered to be 
transient, or even AC - it steps to the applied voltage, then returns to 
zero (or open), then the cycle may be repeated. Each experiment is 
adding or subtracting charge, then reversing the process. Ideally, the 
cap would never lose its DC bias if there were no losses.


The problem is that figuring out all these details may not be trivial. 
It may be more fun to just try some experiments and see how it goes - 
you'll get some idea of how the real thing holds up, and figure what 
amount of C is OK.


*You shouldn't have to worry too much about corona discharge if the 
maximum voltage on anything is below 3 kV or so. Beyond that, it could 
cause problems.


Ed
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Re: [volt-nuts] Bohnenberger electrometer DANGER

2018-03-08 Thread Dr. David Kirkby
On 8 March 2018 at 07:19, Andre  wrote:

> Hi, re. capacitors it might be worth mentioning that the normal equation
> assumes charge and discharge through a constant current.
>

What 'normal equation' do you mean?


> Don't forget that the equation includes a non linear term so you'll need
> to take that into account (Q=CV2 iirc) where Q is Coulombs, C is
> capacitance.
>

I am puzzled by CV2.  The energy (joules) stored in a capacitor is 1/2 C
V^2, where C is the capacitance and V the voltage. I don't know if that's
what you mean.


> If this is done using something like an LM317T in CC mode or even a string
> of them (my idea) with anti-overload circuitry added externally then this
> may well work.
> Any series resistance will cause problems so you'd need quite a lot of
> regulators but there are ways to use JFETs selected by hand if you really
> wanted to
> make a test setup.
>

I am totally lost here!

If anyone has an explanation of whether any of the energy to move the leaf
comes from the battery/capacitor, or does it all come from the charge
applied to the unit, I would like to know.  If no energy (apart from
leakage) comes from the device applying the electric field, a small
capacitor is suitable, and very safe. If at least some of the energy
required to move the leaf comes from the voltage supplying the electric
field, then a small value capacitor will be no use.

This is a fairly low priority task for me at the minute, as I need to do
some real work until Friday evening. But over the weekend I will play with
this.

Dave
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Re: [volt-nuts] Bohnenberger electrometer DANGER

2018-03-07 Thread Dr. David Kirkby
On 7 March 2018 at 06:29, Andre  wrote:

> Please be VERY VERY careful. To be honest its far safer to use CCFL
> drivers and rectify them with camera diodes in series and the absolute
> minimum capacitance for the job, shunted with a high value resistor.
>

The problem with 2.2 nF is it is difficult to know what voltage is on the
capacitor at any time, since with a 10 M ohm multimeter, the time constant
is 22 ms. I have a high voltage probe around somewhere, which probably has
a 100 M ohm input impedance, but that would still only give a time constant
of 220 ms, which is too short to measure easily.

I have 47 uF @ 650 V (or it might have been 550 V) capacitor on order, but
I might go to something a bit lower capacitance if the charge storage is
not required.

I would like to know where the energy comes from to move the leaf. I wonder
if any is taken from the capacitor. In the gold leaf electrometer, with no
internal supply, it is clear the energy much come from the charge on the
plates. But when there's an electric field, that might not be the case. I
was thinking of sticking a 50 uA FSD meter inside, to see if any current is
take from the capacitor, but I don't know if 50 uA would be sufficiently
sensitive to deflect.

Clearly having an electrometer here would be useful for these sorts of
experiments, but I don't have one. I see a reference on here recently to
the Keithley 642 being one of the best, but whilst the basic meters are not
that expensive, the test head and cable are much rarer, so attract a much
higher price.

In any case, there's not a single half-decent electrometer on eBay in the
UK at the minute, and I need it before Monday.


> I have a few inverters , 10M resistor packs and diode strips here if
> anyone has a use on the understanding they are only to be used at your own
> risk, and for the intended purpose.
>
> Microwave capacitors can be deadly (you could DIE!) under the wrong
> circumstances, fibrillation can occur even with quite small shocks down to
> <8J if you get hit badly or have an undetected problem. I don't want to
> scare people but it is a serious risk.
>

It's fairly obvious to me, based on a few quick experiements last night,
that kV is not needed for this. Whilst I'm not doubting one could make an
electrometer (electroscope???) of greater sensitivity using a higher
electric field, this is good enough for a demonstration, and to learn a
bit. For quantitative measurements, I will look for a Keithley
electrometer, at a later date.


> -A
>


Dave
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Re: [volt-nuts] Bohnenberger electrometer DANGER

2018-03-06 Thread Andre
Please be VERY VERY careful. To be honest its far safer to use CCFL drivers and 
rectify them with camera diodes in series and the absolute minimum capacitance 
for the job, shunted with a high value resistor.
I have a few inverters , 10M resistor packs and diode strips here if anyone has 
a use on the understanding they are only to be used at your own risk, and for 
the intended purpose.

Microwave capacitors can be deadly (you could DIE!) under the wrong 
circumstances, fibrillation can occur even with quite small shocks down to <8J 
if you get hit badly or have an undetected problem. I don't want to scare 
people but it is a serious risk.
Had to scale back one of my projects because I had a near miss with a setup 
very much like the one described  in earlier posts and despite dual failsafes 
still got a belt large enough to require medical treatment.
(hint: the experiment is on Youtube, saying no more)
Very fortunately my systems weren't seriously affected but I probably did some 
damage.

Still have a 380J 215uF/2.5KV capacitor here and that one is staying shunted 
and under lock and key until I have the appropriate safety knowledge and 
experience. Dielectric memory is a b*t*h!

-A


From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of ed breya 
<e...@telight.com>
Sent: 07 March 2018 00:11
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Bohnenberger electrometer

I looked at that link that Brooke put up about Bohnenberger's
Electroscope. I don't know what your specific arrangement needs to be,
but it appears you need a plus and a minus HV wrt ground in the most
general form. If so, then this would mean having to split the voltage of
a single cap, or have two caps, one for each polarity.  Then I'd
recommend using good old microwave oven caps. You could charge them both
to say 2 kV from one HV source, then switch them around so they're
stacked and grounded at the midpoint.

Ed

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Re: [volt-nuts] Bohnenberger electrometer

2018-03-06 Thread ed breya
I looked at that link that Brooke put up about Bohnenberger's 
Electroscope. I don't know what your specific arrangement needs to be, 
but it appears you need a plus and a minus HV wrt ground in the most 
general form. If so, then this would mean having to split the voltage of 
a single cap, or have two caps, one for each polarity.  Then I'd 
recommend using good old microwave oven caps. You could charge them both 
to say 2 kV from one HV source, then switch them around so they're 
stacked and grounded at the midpoint.


Ed

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Re: [volt-nuts] Bohnenberger electrometer

2018-03-06 Thread ed breya
Oops - forgot to mention a detail about microwave oven caps. Sometimes 
they have built-in bleeder resistors, which would of course spoil this 
kind of application.  Ed


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Re: [volt-nuts] Bohnenberger electrometer

2018-03-06 Thread ed breya
For static bias, look up "electret" for ideas on some other possible 
options.


I would recommend against your option 2 capacitor - that's a dangerous 
amount of energy to store in something that may be fooled around with 
experimentally. Also, even though it's a lot of C, being electrolytic, 
the charge will eventually leak off anyway - probably faster than any 
charge loss from using the machine.


The option 2 (2 nF at 4.2 kV) seems more appropriate for this use, 
because of the much higher sensitivity attainable. It's charge will leak 
off too, but since it's likely a plastic or oil capacitor, the retention 
time will hopefully be OK overall.


I wouldn't want to take a jolt from either one. In the ultimate design, 
be sure to use some sort of series current limiting resistance to 
isolate the capacitor from the outside world. The R can be quite high 
(megohms, and of course suitable for the maximum voltage) since not much 
current is needed for operation, so the contact/fault hazard would be 
reduced from dangerous to a tingle. It would be good to also have a safe 
discharging method - another R - that can be switched or jammed in, to 
quickly clear the charge for safe keeping when not in use, or during 
design.


In the old days, optical methods were used for "gain," as in a mirror 
galvanometer, for instance. Putting some simple magnification and 
illumination (sun light if electricity is a no-no) in the system can 
increase the visibility of any deflection.


Lastly, regarding capacitors, a good option if available, is to use the 
nice HV oil caps that can be salvaged from older-era (before they went 
to switching supplies) microwave ovens. These are typically rated around 
1 uF, 2 kV AC. Two in series would do for up to 4-5 kV service. Since 
you don't want bleeder/balancing Rs in this application, it would be 
best to use identical caps, or slightly more complicated charging 
circuitry. They can bought new, but may be pretty spendy, depending on 
the project budget. I have dozens of them - saved from every microwave 
oven I've junked out over the years.


At 1 uF, these would have much better retention time, with hazard energy 
between the original options.


Ed

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Re: [volt-nuts] Bohnenberger electrometer

2018-03-06 Thread Brooke Clarke

Hi Dave:

Here's a free on line book "Magnetism and Electricity", 1877
https://books.google.com/books?id=y45PYAAJ=PA169#v=onepage=false
Chapter 6 Electroscopes and Electrometers starts on book page 74 (pdf pg 81)
but . .
Chapter 11 Voltaic, Dynamical or Current Electricity is where paragraph 214 Bohnenberger's Electroscope appears on book 
pg 169 (pdf 176).

This is the chapter for the Voltaic Pile so that's probably why since it's a 
way to testing polarity.

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

 Original Message 

Bohnenberger electrometer


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