Re: [volt-nuts] Bohnenberger electrometer

[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

[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

[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

[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

[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

[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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