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High voltage probe for O-scope, 2 of 2, ( FABRICATION ).

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Patrick

Mon Sept 26 2011, 08:34AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

This thread will be dedicated to the fabrication and operation of the final probe design. Any replies should be with that understanding of intent and the normal project thread rules. All other comments, criticism and suggestions should be made to this thread:

High Voltage probe for O-scope, 1 of 2, ( DEVELOPMENT ).

(Compensation circuits have been posted on the "Development" thread.)

Otherwise Please comment!

Background info:

Sam Goldwasser's HV probe page...

Marco Denicolai's explanation of his 20 liter water HV probe (600kV).
[Note what i have highlighted in green.]
His PDF is here:

Marco's tesla and thesis site:

Background Info End.

These next few pics show the construction of what i call the "High Voltage RC Element", this device is a SSX39 MG resistor,
125 Mohms in parallel with a coaxial 4.9-5.2 pF oil capacitor, both are meant to withstand 14 kV. 3 of these "elements" will be in series to obtain a 42 kV probe of 375 Mohms, at 1.5 to 1.7 pF. I just pray the field distrubution and capacitence is enough, the Northstars have 10 pF for a similar spec'ed probe. The bottom most plate is insulated from the resistor body, as the voltage drop beneath it is 800 volts less then the plate. This probe will be food oil filled and have a 10,000:1 division ratio.

Sheet metal and copper ring.

Plates of steel and copper soldered and epoxied, then attatched as per the FEMM model for field distrubution.

Temporary hot glue mock up to test fit and funtion, this will be redone in oil proof epoxy soon.

A single HV RC element seen here in my hand.

The resistor's V drop is linearized with the cap plates, and grading rings.

Zoey, best dog ever, on quality control.

Insulator is acrylic should be good for 50kV+

****************************************** *****

[Gen 5, Type 3, Mod 6, Rev J, Ver 3.0, Attempt 12]

Final schematic, as it will be built in the next 7-10 days.

C5 should be variable from 294 pF to 319pF, which will allow an oscope with 7-30pF internal capacity to be compensated.

The Ross Engineering, NorthStars, and the patent, as well as my probe all have one adjustment, to calibrate/compensate. This is a significant advantage over the 5 or more pots and trimmers the Tek p601(3,4,5)'s had.

******************************************** ************

Oil Drain, and bottom end of the HV section.

More to come soon!

Patrick

Sat Oct 01 2011, 05:16PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I used this cheap circuit predrilled stuff but it was so weak, while making the piece i needed, it broke apart in my fingers. Ill need to use the real FR4 circuit board stuff then, its hard to cut though.

Patrick

Tue Oct 04 2011, 06:40AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

[Gen 5, Type 3, Mod 60, Rev J, Ver 3.0, Attempt 12]

Final schematic, as it will be built in the next 7-10 days.

Mattski

Tue Oct 04 2011, 03:57PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Is that 50 Ohm resistor actually part of the BNC connector? I would expect the connector to just have some stray capacitance and no resistance.

Patrick

Tue Oct 04 2011, 04:10PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Mattski wrote ...

Is that 50 Ohm resistor actually part of the BNC connector? I would expect the connector to just have some stray capacitance and no resistance.

Im going to add the resistor and capacitor, very close the the BNC connector, the connector is just the common straight through type.

When I add it, it will probably be a tube/bulge cover by heatshrink tubing.

Mattski

Tue Oct 04 2011, 04:19PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Ah I see, I had thought that you were modeling the effects of the connector as a resistor and capacitor.

Patrick

Tue Oct 04 2011, 04:49PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Mattski wrote ...

Ah I see, I had thought that you were modeling the effects of the connector as a resistor and capacitor.

Nope.

I also want to make a 1 or 3 kV square wave calibrator at 1-10 kHz.

EDIT new work :

Oil drain.

Patrick

Thu Oct 13 2011, 12:51AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

New method for removing the silicone conformal coating from the caps, using MEK.

cap plates will be added shortly.

Sulaiman

Thu Oct 13 2011, 04:05PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Patrick,
" I also want to make a 1 or 3 kV square wave calibrator at 1-10 kHz."

How will you calibrate the calibrator?

Patrick

Thu Oct 13 2011, 07:03PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Sulaiman wrote ...

Patrick,
" I also want to make a 1 or 3 kV square wave calibrator at 1-10 kHz."

How will you calibrate the calibrator?

It only needs to have a high rise and fall time. IE, a square wave, like what is on the front of the oscilloscopes for compensation. (and serving the same purpose.)

The Tek, northstars, ross engineering and mine have pretty high accuracy from DC to 100Hz (like 0.1%) , yet the accuracy worsens towards 50MHz (like 3-5%).

Thus my HF probe and the others (except the tek P60** series) only need a single compensation screw.

The tek P6015 has 900 pots and trimmers right? turn this one a weee bit this way, the next a weee bit the other way.... then do it again, and again, and again.

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