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4hv.org :: Forums :: High Voltage
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High voltage probe for O-scope, 1 of 2, ( DEVELOPMENT ).

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Patrick
Fri Feb 04 2011, 04:56AM Print
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
[Gen 4, Type 3, Mod 40, Rev H, Ver 2.0, Attempt 9] for HV O-scope Probes.


Ive been reading this...
]us5107201hvprobe.pdf[/file]


1296795379 2431 FT0 75mandc
14awg wire copper. 75M ohm, 20kV, 3.4W resistor with the main resistive material cut.


1296795379 2431 FT0 75mandco
I presume the curve will decrease field intensity better then the angled one.


1296795379 2431 FT0 75mandct
2.0pF in air, 4.0pF in olive oil. I had to destroy this resistor to make the capacity measurement, I ground through the Ruthenium-oxide resistive element. before with a good resistor my C meter said 0.8pF - 0.0pF (@ 2Vrms into 75M ohms!) after cutting it, it read a stable 4.0-4.2 pF in oil.
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Pinky's Brain
Fri Feb 04 2011, 02:06PM
Pinky's Brain Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
If you make a divider as tall and for as much voltage as the North Star VD probes you will be left with << 1 pF ... whereas North Star has ~20 pF, and that capacitance isn't there for naught.

This seems only enough for a handheld probe with one or 2 resistors.
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Proud Mary
Fri Feb 04 2011, 02:38PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
It suggests a skeletonic version of the individual resistor shielding arrangements in the Park Resistor standard.
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Patrick
Fri Feb 04 2011, 03:34PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...

If you make a divider as tall and for as much voltage as the North Star VD probes you will be left with << 1 pF ... whereas North Star has ~20 pF, and that capacitance isn't there for naught.

This seems only enough for a handheld probe with one or 2 resistors.
Two in series was my target. I was warned that too much capacity would limit bandwidth or rise time.


Proud Mary wrote ...

It suggests a skeletonic version of the individual resistor shielding arrangements in the Park Resistor standard.
I technically wasnt shielding the resistor with the cap, have'nt got that far yet.

Park resistor thread Link2
Park resistor PDF Link2
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Patrick
Mon Feb 07 2011, 05:48AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...

To me it seems that a handheld probe is significantly harder to design than a standalone probe connected through a low induction copper strap. With a stand alone probe you can keep the electric field across the HV resistor uniform (like your capacitive hoops in the other thread) which simplifies modelling it's operation.

The moment you put a grounded metal shield around it which goes close to the tip the behaviour of the system becomes much harder to predict.
The NorthStar's do have a large topand bottom ring, to equalize the field and as you said I guess thats where some capacity comes from too.

I believe the Tek P6013, P6014, P6015 all have that metal shield so they can treat the whole path as a lossy-transmission line?

Im aiming for these:
300M for 24kV, 2 Probes
600M for 45kV, 3 Probes (0ne of these will be a +-1% calibration standard)
800M for 60kV, 2 Probes
1.40G for 100kV, 1 probe

What about this...

1297057067 2431 FT107663 Hfhv1
Yellow are copper "Park-like" Caps, Red are resistors. The bottom most section are where compensation and LV componets live. ( Approx. 14" tall )


1297057067 2431 FT107663 Hfhv2



1297057067 2431 FT107663 Hvhf3
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Patrick
Wed Feb 09 2011, 02:20AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Exceprts from "High Voltage Engineering Fundamentals" E. Kuffel, W.S. Zaengl. Pergamon Press.

isbn: 0-08-024213-8


1297217997 2431 FT107837 Sam 0396crfopped
4 main types of dividers.


1297217997 2431 FT107837 Sam 0396cropped
Type (a) is my most favored design, though there is a thread i started which shows another like type (d).



1287214224 2431 FT91689 Hvpic
Damped resistor type, as seen in fig (d).(actually this is a composite of (a) and (d).)



amazed amazed amazed
look at page 2 !




1297217997 2431 FT107837 Sam 0382cropped
The "Park" idea yet again


1297217997 2431 FT107837 Sam 0388cropped
capacitence distributed
across the length of the resistor.


1297217997 2431 FT107837 Sam 0390cropped
field gradient.


1297237181 2431 FT1630 Sam 0380cropped


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Patrick
Thu Feb 10 2011, 01:57AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Construction of the next prototype will now commence

related thread: Link2
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Patrick
Tue Feb 22 2011, 07:24PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Updates and Pics.

Ive had real problems with the caps here, please comment. ive had series capacitence be larger than the parallel cap ? what, how is that possible?! And, ive had each cap very from 1.1 pF to 3.3pF, now i think there stable at 2.3 to 2.8 pF each. I think there both actually close to 2.5 pF, and the dimensions are withins thousandths in any dimension, so i dont see how it can vary unless its other objects on the table that bias them. Also, the tubes have the same half circle radius as the pipe wall thickness (0.040")

Please comment and advise me if im totally wrong, or if you have a better set up for measuring pF's in the single digit range.

1298402671 2431 FT107837 Sam 0425
Basic Components, tubes for caps, and two 200Mohm resistors.


1298402671 2431 FT107837 Sam 0426
resistors were ground through till open circuit, so as to not effect the Picofarad measurements.


1298402671 2431 FT107837 Sam 0431
Assembly and scale.


1298402671 2431 FT107837 Sam 0446
Olive oil, 2.4 pF, and cap check at 0.570" gap. (copper spool support)


1298402671 2431 FT107837 Sam 0452
Left cap at 2.8 pF, 0.570" gap. (copper spool support)


1298402671 2431 FT107837 Sam 0454
Right cap at 2.5 pF, 0.570" gap. (kool-aid support)



1298402671 2431 FT107837 Sam 0455
Series cap is 1.1pF. (kool-aid support)



1298402671 2431 FT107837 Sam 0457
Left cap at 2.5 pF, 0.570" gap. (kool-aid support)


1298402671 2431 FT107837 Sam 0458
Plan view, top.


1298402671 2431 FT107837 Sam 0459
Isometric view, side.


1298402671 2431 FT107837 Sam 0460
Caddock.
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Proud Mary
Tue Feb 22 2011, 08:08PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Have you measured the capacitance between the two meter leads on their own - terminated in the oil bath with nothing attached to their ends? You have to account for, or null out, stray capacitance somehow.
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Patrick
Tue Feb 22 2011, 08:12PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...

Have you measured the capacitance between the two meter leads on their own - terminated in the oil bath with nothing attached to their ends? You have to account for, or null out, stray capacitance somehow.
yes, nulling was the first thing I did, multiple times throughout the day/experiment. And got multiple consistent results, so I belive the meter. (i even was careful with how close and the shape of those two wires)

I think pF measurements are just prone to alot of crap?

Also, proud mary this is my interpretation of the "park" concept.
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