RE: Water probe II

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Denicolai, Marco" <Marco.Denicolai@xxxxxxxxxxx>

Hi Bob,

> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: 28. joulukuuta 2004 03:44
> To: tesla@xxxxxxxxxx
> Subject: Re: Water probe II
>
> Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>
>
> Hi,
>
> I thought I posted a message to you about high Z problems
> when you first suggested using pure water.  But apparently it
> only made it to a draft sorry.

That message would be welcome :)

> Is your simulation software full 3D simulating distributed R
> and C?  If so that a nice tool.

It's 2D but it can do axis simmetrical (rotate around the Z axis).
That's what I'm using. This software is freeware.

> If you can design a high bandwidth high impedance divider it
> would be very useful to the list.

Indeed.

> Note your make shift hand on the top and hand on the side
> that improves the response is effectively a parallel C
> between the input and output that compensates for the self C
> of the probe as is done on regular scope probes.
> Apparently some high voltage probes use an adjustable
> cylinder to achieve the that.

More info about how that connection is engineered would be welcome too.
Namely the capacity between the hot terminal and the water column has to
be increased. That means that the top voltage has to be capacitively
coupled to the water column. How to avoid corona and dielectric
breakdown?
Last evening I tried with a metallic collar crimped on the water column
tube and connected to the HV electrode. That did improve very much the
response. But how to practically build that? An extra water "cylinder"
around the original one seems to be easier to be implemented.

> If your going to experiment with the inner outer thing here
> are some of my thoughts.  Add an air gap between the inner
> and outer to reduce the C between them and therefore more
> tolerant of differences in voltage.  In the limit this is say
> 1/4in inner tube with a 2in air gap. If one outer improves
> things perhaps two outers are even better and allow high R
> for all of them.

On the big probe I have got empty space from the probe bottom (hot) up
to abot 40% of its height (see the drawings on my web pages). If I fill
it with a liquid it is automatically connected to the hot terminal.
That's perfect. I think I should fill it with a conductive solution
(CuSO4) to emulate my "hand" on the probe smaller model. Changing the
fill "height" should provide a capacitive coupling tuning to the HV
electrode.

> You will still need high Z amp to avoid loading on the inner.

I'm going to build a video amplifier for a 50 ohm load.

Best Regards