Questions about a simple HV scope probe (20kV - DC and AC 50Hz) / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Questions about a simple HV scope probe (20kV - DC and AC 50Hz)

previous 1 2 3 next

Move Thread

LAN_403

PhilGood

Wed May 29 2013, 08:17AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Thanks Tony for these calculations, it is really interesting

I have a new idea for insulation: I could use these laser transparencies people use for DIY HV capacitors. These transparencies are said to stand 10+kV:

So I should be fine with 10 layers. I would just roll them inside the PVC pipe. And doing this I can even use a smaller (1/2 ") PVC pipe for the front part of the probe, this would give the whole thing a better look.

Steve Conner wrote ...
The resulting frequency response can have a practically infinite number of poles, needing a complex compensation network. Tektronix's P6015 probe is a great example of this school of thought.

Indeed, seven adjustments

Voltcraft makes a probe like the one I want to build, retail price is around 90â‚¬

Datasheet:

Tony Matt

Thu May 30 2013, 03:24AM

Registered Member #3700 Joined: Sat Feb 19 2011, 12:59PM
Location:
Posts: 107

what could be the damage if the capacitor get a short circuit??

EDIT :

I'm refering to the DIY capacitors that you want to use .
If this cap is connected in PARALLEL with the 200megohm resistor, and if this cap get a arc or fail, the 50 kV will be connected to your scope or vtvm...

The same with the oil, we do not know the olive oil beavior under so much voltage... Leave the prober dry and avoid a lot of trouble ...

PhilGood

Thu May 30 2013, 06:41AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Tony Matt wrote ...

what could be the damage if the capacitor get a short circuit??

Which capacitor ? I don't get your question ... sry

EDIT: I wasn't planning to add any capacitor to my design, my idea is just to roll one of these transperencies sheet inside my PVC pipe for insulation

Steve Conner

Thu May 30 2013, 09:54AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I imagine it would cause an "earth-shattering Kaboom".

HV Enthusiast

Thu May 30 2013, 12:28PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Regarding high voltage probes. Just recognize that layout and the types of oil or other potting material will greatly affect the overall frequency response of the hv divider.

Getting high bandwidth isn't too difficult, but getting high bandwidth with a flat response across the entire band, is EXTREMELY DIFFICULT.

PhilGood

Thu May 30 2013, 11:58PM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Hi EVR,

I understand all the difficulties one may face when trying to build an HV probe with a high bandwith.

But my project is for a DC and AC 50Hz probe so I should be fine

As I said above I already gave up with using oil for insulation, I'll use a few layers of laser transparencies instead

Btw, do you have any pic you could share of your HV Probe described here

(finished probe, and construction pics showing components)
Would be much appreciated

Shrad

Fri May 31 2013, 07:24AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

If you wish I have for sale a high voltage probe which would suit your needs (vintage 50's with original box and manual)

Patrick

Mon Jun 03 2013, 07:52PM

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

wrote ...

Hi steve :)

Steve Conner wrote ...
There is no such thing as a simple HV scope probe.

Indeed I've seen that reading some threads here dedicated to this subject like Patrick's Project

Thanks for the detailed answer with values and calculations, this is quite instructive.

Yay! my work has been quoted, that will float my ego for a while.

im not sure I did get a totally flat frequency response, even with my final best probe. But its a difficult task at MhZ periods.

for your dc and lo freq app, ill remind us all of Proud Mary and my own embarrassing oversight. using very high value (1Gohm) resistors and very low input current DMM, we had inexplicable slow oscillations even at 20Hz, where it would oscillate from a 20 kv known source, down to 7kv, the slowly to 80kv over 20-40 seconds. this was a coupled tiny leak capacity and very high Ohm impedance causing a RC with current drain to yield a totally bogus measurement

these devices a hard to get right, even at low freq. though DC is easier.

I put up several threads over 3-4 years here as my need was great, and there were no or few instruments described online, and fewer still that average tinkerer could build on there own.

id like steve Connors point on complex mulit-pole compensation elaborated on please...

The Lightning Stalker

Mon Jun 03 2013, 10:13PM

Registered Member #4230 Joined: Sat Nov 26 2011, 05:50AM
Location: Socketville
Posts: 53

DO NOT use olive oil! It will go rancid and its properties will change. If you must use oil, use minerail oil. It is better though to pot it in silicone or fiberglass resin.

The whole thing should be shielded with some type of foil as best you can.

Patrick

Wed Jun 05 2013, 04:36PM

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

several of us have used olive oil for precision instruments, and canola for common instruments, and in 3+ years the device oil is clear and normal in color... the problem with ridged potting like epoxy, is that if it isn't done right you can have age change the surface bond on the HV device body to epoxy surface, and have a void which fills with air, then supports corona.

soft silicone and oil, don't have that potential problem. and besides oil cools way better than epoxy or silicone. Non-detergent engine oil, and mineral oil are exceptable. though if you can get real electrical oil from shell or exxon that would be best.

olive oil has excellent electrical properties for fast HV waves and such, with excellent age stability. However corn oil is just worthless.

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob