Bohnenberger electrometer
On 6 March 2018 at 09:40, Dr. David Kirkby drkirkby@kirkbymicrowave.co.uk
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
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 drkirkby@kirkbymicrowave.co.uk
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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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
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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Yes Hendrik, same principle as the butterfly disk style, but mine use
cylinders - the field exposure is radial instead of axial. Ed
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 <eb@telight.com> 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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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 drkirkby@kirkbymicrowave.co.uk wrote:
On 6 March 2018 at 09:40, Dr. David Kirkby drkirkby@kirkbymicrowave.co.uk
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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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.