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Author Topic: Splitting the Negative  (Read 17651 times)

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Brad,

my experience is that things are far more complicated then it seems at first glance (like charge is stored in the dielectricum).
Its probably not the dielectricum itself, but a combination of things like distance, matter, etc. and way beyond my present level of comprehencion.

But i am sure someone will be able to explain it in great detail.

 
Itsu

I think gaining a good understanding of what is happening here,would unlock so many doors.

I have one of those old multi plate tuning caps,so I'll  try the experiment tonight.


Brad


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Brad you should know this one O0

http://ultrabattery.com/

From your part of the world, combined capacitor and battery, very easy to make

Regards

Mike 8)

No Mike--havnt seen that one yet--but have now. O0


Brad


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Ok,so i placed a diode on one side of a multiplate tuning air capacitor from an old radio.
I then pulsed the capacitor with my SG,using a square wave,at 50% duty cycle, at a frequency of just 6 Hz

I then took one scope shot without air being blown between the plates,and another with air being blown between the plates.
The air supply was from the blow gun of my compressor,at 80psi--so a lot of air passing between all the plates.

Below are two scope shot's.

The first shows the discharge rate without air being blown between the plates.
The second shows the discharge rate with air being blown between the plates.

Even at this low frequency,and a very high volume of air being blown between the plate's,i do not see any difference at all between the scope shots.

If the dielectric (in this case-air) is what holds the charge,why do we see no difference at all between the two scope shot's ?.

Should not the charge be blown away,when uncharged air is continually being injected between the plates?.


Brad


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Hi Brad.

You must have some pretty low humidity at the moment?

I once tried a simple experiment using an Aluminium flexible sheet, a little bit heavier gauge than foil. Just by waving it around a bit it in the air it became charged. Could the flowing air be charging the plates?

How do you think the reverse would be? Try evacuating the air by using your compressor in reverse?

Cheers Graham.


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Hi Brad.

You must have some pretty low humidity at the moment?

I once tried a simple experiment using an Aluminium flexible sheet, a little bit heavier gauge than foil. Just by waving it around a bit it in the air it became charged. Could the flowing air be charging the plates?

How do you think the reverse would be? Try evacuating the air by using your compressor in reverse?

Cheers Graham.

No.
I tried blowing the air through the plates,without the SG hooked up--just to look for that very thing.
But not 1mV seen on the scope.


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Ok,so i placed a diode on one side of a multiplate tuning air capacitor from an old radio.
I then pulsed the capacitor with my SG,using a square wave,at 50% duty cycle, at a frequency of just 6 Hz

I then took one scope shot without air being blown between the plates,and another with air being blown between the plates.
The air supply was from the blow gun of my compressor,at 80psi--so a lot of air passing between all the plates.

Below are two scope shot's.

The first shows the discharge rate without air being blown between the plates.
The second shows the discharge rate with air being blown between the plates.

Even at this low frequency,and a very high volume of air being blown between the plate's,i do not see any difference at all between the scope shots.

If the dielectric (in this case-air) is what holds the charge,why do we see no difference at all between the two scope shot's ?.

Should not the charge be blown away,when uncharged air is continually being injected between the plates?.


Brad

OK, this is interesting.  Not being that familiar with the Rigol scopes, what does the "D 85.14ms" indicate and, I assume the "H 500us" is the horizontal sweep rate/division?  Just trying to evaluate the velocity of the moving air verses the discharge time period.

Regards,
Pm
   
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OK, this is interesting.  Not being that familiar with the Rigol scopes, what does the "D 85.14ms" indicate and, I assume the "H 500us" is the horizontal sweep rate/division?  Just trying to evaluate the velocity of the moving air verses the discharge time period.

Regards,
Pm

The "D 85.14 ms" indicates that the trigger point is 85.14 ms from screen center, off to the left. Also indicated by the little orange arrow symbol "T" at top left pointing to the left.  The "H 500 us" is the horizontal time per division setting.

   
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The "D 85.14 ms" indicates that the trigger point is 85.14 ms from screen center, off to the left. Also indicated by the little orange arrow symbol "T" at top left pointing to the left.  The "H 500 us" is the horizontal time per division setting.

Thanks TK.  My knowledge of fluid dynamics is sorely lacking so I'm unable to go any farther with this!

Regards,
Pm

Edit:
   

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Thanks TK.  My knowledge of fluid dynamics is sorely lacking so I'm unable to go any farther with this!

Regards,
Pm

Edit:

If the charge is stored in the dielectric,and in this case,the dielectric is the air,i would have thought we should have seen a reduction in time the cap took to discharge,and a decrease in charge, when the air was being blown between the plates,as the charge would have been removed along with the air being removed during the charge and discharge cycles.

But as you can see,there is no change at all--and we are talking about a very small value in capacitance-a low frequency cycle rate,and a high volume of air exchange.

So,in this case,it dose not seem like the charge is stored in the dielectric  ???__> have we talked our selves  into believing that it is,due to what we !think! we have seen in the video's posted so far?.

Maybe it is like Itsu said--there maybe more than meets the eye here?.


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Ok,so i placed a diode on one side of a multiplate tuning air capacitor from an old radio.
I then pulsed the capacitor with my SG,using a square wave,at 50% duty cycle, at a frequency of just 6 Hz

What is the number of the diode you used and what is the capacitance of the variable cap when closed?  It is possible the capacitance of the reverse biased diode is the major contributor to the overall capacitance being discharged which would definitely affect the results.  Is a 10Meg scope probe used to discharge the cap?

Quote
I then took one scope shot without air being blown between the plates,and another with air being blown between the plates.
The air supply was from the blow gun of my compressor,at 80psi--so a lot of air passing between all the plates.

Below are two scope shot's.

The first shows the discharge rate without air being blown between the plates.
The second shows the discharge rate with air being blown between the plates.

Another factor that could be affecting these results is that the time constant appears to be ~750us which would mean 5T ~ 3.75ms.  At 6Hz, the "on" time would be 83.3ms which is 83.3/3.75 ~22x the discharge time.  IOW, you are possibly creating a large number of electrostatic domains around the test cap during the long charge period that could affect the results.

Quote
Even at this low frequency,and a very high volume of air being blown between the plate's,i do not see any difference at all between the scope shots.

If the dielectric (in this case-air) is what holds the charge,why do we see no difference at all between the two scope shot's ?.

Should not the charge be blown away,when uncharged air is continually being injected between the plates?.

Yes, one would assume so. 

Perhaps a more conclusive test setup would be to test the variable cap with just a touch from a positive source, then setup the scope to trigger at approximately half that value on a rising edge and discharge the cap with the scope probe.  Try charging and discharging this setup until you have consistent results.  Then, charge the cap, put a short burst of air to the cap and then discharge with the scope probe and compare the results.

Quote
Brad

Regards,
Pm
   

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What is the number of the diode you used and what is the capacitance of the variable cap when closed?  It is possible the capacitance of the reverse biased diode is the major contributor to the overall capacitance being discharged which would definitely affect the results.  Is a 10Meg scope probe used to discharge the cap?

Another factor that could be affecting these results is that the time constant appears to be ~750us which would mean 5T ~ 3.75ms.  At 6Hz, the "on" time would be 83.3ms which is 83.3/3.75 ~22x the discharge time.  IOW, you are possibly creating a large number of electrostatic domains around the test cap during the long charge period that could affect the results.

Yes, one would assume so. 

Perhaps a more conclusive test setup would be to test the variable cap with just a touch from a positive source, then setup the scope to trigger at approximately half that value on a rising edge and discharge the cap with the scope probe.  Try charging and discharging this setup until you have consistent results.  Then, charge the cap, put a short burst of air to the cap and then discharge with the scope probe and compare the results.



Regards,
Pm


PM,

using 2 big variable air capacitors (345pF each) parallel gives 680pF.
Plates on max. capacitance and loaded with 24V.

Attaching the groundlead of the scope to the fixed plates, and touching the probe tip to the variable plates shows this scope signal, see picture.
It that the kind of signal you would expect?

Itsu
   
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PM,

using 2 big variable air capacitors (345pF each) parallel gives 680pF.
Plates on max. capacitance and loaded with 24V.

Attaching the groundlead of the scope to the fixed plates, and touching the probe tip to the variable plates shows this scope signal, see picture.
It that the kind of signal you would expect?

Itsu
Itsu,

Thanks for doing this test!  Yes that is what I would expect only I used a positive polarity but the test will work fine with a negative source and pulse.  IOW, if you have the stator plates grounded and apply a quick positive voltage to the rotor plates , then touch your probe to the rotor plate, you should see a fast rising positive positive pulse that slowly decays from the probe resistance.  So, the polarity really doesn't matter and it appears that you are ready to test with a short burst of air thru the plates to compare with the static conditions.

If you have consistent static tests, you could save the discharge profile in one of your Ref channels so it could be compared to the discharge profile after air has been applied to the variable cap.

Regards,
Pm
   
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Why do vacuum capacitors work?

https://en.wikipedia.org/wiki/Vacuum_variable_capacitor

As I understand it, the dielectric constant of air is 1.0006 compared to a vacuum of 1.0000.  Hardly much difference, so electric dipoles would be possible in a vacuum resulting in a capacitance slightly less than than that in air with equal plate dimensions.

Regards,
Pm
   

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Hmmm,

unexpected results.

OK, same setup as above (2x 345pF air variable caps parallel at max. capacity (960pF measured))
Loading with 24V for 1 second the moveable plates with the return lead connected to the static plates.

After 5 second touching with the probe tip (ground lead / return lead still on the static plates) the moveable plates.


Done it twice, see screenshot the first 2 peaks Ref1 and Ref2.  (23.xV)
Then in those 5 second waiting time blowing air (with my mouth) inbetween the plates, see 3th peak Ref 3 (out of scale, so clipping).
Then after adjusting the vertical setting again blowing air inbetween the plates, see yellow CH1 peak (110.4V)  :o


So there surely is a huge difference.

Itsu
   
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Hmmm,

unexpected results.

OK, same setup as above (2x 345pF air variable caps parallel at max. capacity (960pF measured))
Loading with 24V for 1 second the moveable plates with the return lead connected to the static plates.

After 5 second touching with the probe tip (ground lead / return lead still on the static plates) the moveable plates.


Done it twice, see screenshot the first 2 peaks Ref1 and Ref2.  (23.xV)
Then in those 5 second waiting time blowing air (with my mouth) inbetween the plates, see 3th peak Ref 3 (out of scale, so clipping).
Then after adjusting the vertical setting again blowing air inbetween the plates, see yellow CH1 peak (110.4V)  :o


So there surely is a huge difference.

Itsu

Itsu,

OK, if I understand correctly, after charging the capacitor, you blow thru the plates, discharge with your scope probe and then measure a larger peak pulse than without blowing thru the cap.  If correct, my interpretation is that since Q=CV or V=Q/C and with the voltage being greater after blowing, you increased the charge between the capacitor plates.  The only other option is that your breath has a lower dielectric constant than air and has lowered the capacitance ???.  What in the world have you been drinking :).  Seriously, the charge has to have increased but I don't know how at this point!

Regards,
Pm
   
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As I understand it, the dielectric constant of air is 1.0006 compared to a vacuum of 1.0000.  Hardly much difference, so electric dipoles would be possible in a vacuum resulting in a capacitance slightly less than than that in air with equal plate dimensions.

Regards,
Pm

Dipoles of what?

https://en.wikipedia.org/wiki/Vacuum_polarization
   
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Itsu,

OK, if I understand correctly, after charging the capacitor, you blow thru the plates, discharge with your scope probe and then measure a larger peak pulse than without blowing thru the cap.  If correct, my interpretation is that since Q=CV or V=Q/C and with the voltage being greater after blowing, you increased the charge between the capacitor plates.  The only other option is that your breath has a lower dielectric constant than air and has lowered the capacitance ???.  What in the world have you been drinking :).  Seriously, the charge has to have increased but I don't know how at this point!

Regards,
Pm

What's the difference between the relative permittivity of dry air (room air) and moisture-saturated, CO2 enhanced, oxygen depleted air (Itsu's breath)?
   

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Ok, OK,  you got me there guys, i won't be drinking and benching (as in working on the bench) anymore.  :P

But seriously, PM, you are correct how i did it, so that was not such a good idea i guess to breathe instead of using a blower or fan.
I will repeat that test using such a fan.


But the goal was to replace the charged air (dielectric) by some fresh uncharged air to see if the charge was gone.
It really should not matter if i replace the charged air by moistured air,    i think.


We will see,  itsu
« Last Edit: 2017-12-17, 11:04:35 by Itsu »
   

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OK, redid that same test again, (24V from a battery stack) now with both breathing and using a fan.
Again the breathing shows peaking (3th peak) while the fan (4th peak) shows normal amplitude.

Screenshot shows first 2 peaks are without breathing/blowing, 3th is breathing, 4th is using a 12V fan blowing air between the plates.

So it seems that the charge is NOT contained in the air (dielectricum) between the plates.

TK,  so what is the difference?

Itsu
   
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Dipoles of what?

https://en.wikipedia.org/wiki/Vacuum_polarization

Electric dipoles as in-

https://en.wikipedia.org/wiki/Electric_displacement_field

Quote "In a dielectric material the presence of an electric field E causes the bound charges in the material (atomic nuclei and their electrons) to slightly separate, inducing a local electric dipole moment."

Pm
   
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What's the difference between the relative permittivity of dry air (room air) and moisture-saturated, CO2 enhanced, oxygen depleted air (Itsu's breath)?

Don't know the answer to this so, let's make some assumptions regarding Itsu's breath in his initial test.  If his breath had a higher dielectric constant than the ambient air, this would have the effect of increasing the capacitance between the cap plates.  This along with the initial charge should have produced a lower peak discharge voltage but this was not the case.  The only option then is that his breath has a dielectric constant <1 so is this the answer?

Pm
   
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All,

Ok, I set up a two plate test capacitor that would allow a .010" thick piece of polycarbonate material to be moved and removed if necessary to confirm the previous test results as described in my post #23 which I have run many times in the past.  All my previous results indicated that the charge was stored in the dielectric.  At this moment in time however, I can not repeat those test results so I'm presently a little confused with the results I am seeing.

Regards,
Pm
   
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Electric dipoles as in-

https://en.wikipedia.org/wiki/Electric_displacement_field

Quote "In a dielectric material the presence of an electric field E causes the bound charges in the material (atomic nuclei and their electrons) to slightly separate, inducing a local electric dipole moment."

Pm

Certainly. But aren't we talking about _vacuum_ capacitors? What dielectric material contains bound charges that can separate and create a dipole moment in a vacuum capacitor?
   
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Don't know the answer to this so, let's make some assumptions regarding Itsu's breath in his initial test.  If his breath had a higher dielectric constant than the ambient air, this would have the effect of increasing the capacitance between the cap plates.  This along with the initial charge should have produced a lower peak discharge voltage but this was not the case.  The only option then is that his breath has a dielectric constant <1 so is this the answer?

Pm

Certainly there are differences in relative permittivity between dry ambient air and exhaled air that is saturated with moisture. Not much though. Can we hope to detect the difference between, say, the permittivity of the vacuum, and the permittivity of air moist or dry, with our benchtop equipment? A few parts per ten thousand?

I think that moist exhaled air will be more conductive than dry ambient air.

   
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