[Prev][Next][Index][Thread]

Re: Capacitor C/Peek



>>From couturejh-at-worldnet.att-dot-netSun Nov  3 22:19:13 1996
>Date: Sun, 3 Nov 1996 07:45:49 +0000
>From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
>To: tesla-at-pupman-dot-com
>Subject: Re: Capacitor C/Peek

>At 05:26 AM 11/2/96 +0000, you wrote:
>>From rwstephens-at-ptbo.igs-dot-netFri Nov  1 21:53:34 1996
>>Date: Fri, 1 Nov 1996 23:55:01 -0500
>>From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
>>To: tesla-at-pupman-dot-com
>>Subject: Re: Capacitor C/Peek
>
>>>>From ed-at-alumni.caltech.eduThu Oct 31 22:44:27 1996
>>>Date: Thu, 31 Oct 1996 18:09:07 -0800 (PST)
>>>From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
>>>To: tesla-at-pupman-dot-com
>>>Subject: Re: Capacitor C/Peek
>
>>>Re:
>>>"
>>>|any accuracy when attempting to measure voltages by spark length.  I have
>>>|plans
>>>|to build a directly connectable HV capacitive divider probe this year
>>>|for the lab with a capability of at least 500 kV with accurate
>>>|frequency response for waveform analysis.  This will be a very useful
>>>|instrument with which many questions might be answered."
>>>	When this is available it should produce some very interesting
>>>data of spark length vs voltage vs time etc.  Hope we will all get
>>>to see the results (and perhaps suggest other experiments).  I
>>>have always felt such a capacitive divider is the ONLY way to make
>>>any meaningful measurements.
>>>Ed Phillips
>>
>>Ed, All,
>>
>>I will keep you all posted on this project.  It is a few months away 
>>though.
>>
>>rwstephens
>>
>-----------------------------------------------
>
>Connecting anything to the secondary terminal of a Tesla coil will lower the
>voltage and give an erroneous voltage reading. A better method would be to
>measure the electric field which Breit, Tuve, and Dahl did with their 5
>million volt coil in the 1930's as shown in the Tesla Coil Construction
>Guide. The problem is that it is difficult to calibrate the measuring setup.
>It is more difficult and probably impossible to calibrate the method you are
>contemplating.

>I agree, however, that it would be nice to have a better method than the
>present wild guess spark length method. One possibility is the CSL method or
>controlled spark length. Whatever it is it has to be simple and inexpensive
>or coilers won't use it.
>
>However, don't let me discourage you as you might hit on something good.
>
>Jack C.

Jack,

The capacitive voltage divider probe which I propose will have very 
low terminal capacitance (5 pf or less).  If it becomes permanently attached 
to the Tesla coil under test, and the Tesla coil is tuned for max 
output with the probe connected, the probe merely becomes a part of 
the top load of the Tesla coil.  There will,  under these conditions, 
be no measurement errors or coil efficiency losses.  

I have a direct connection 100 kilovolt RF capacitive divider probe made 
by Machlett.  It has a ratio of 500 to 1.  I plan to use it to 
calibrate my custom made probe.  I will attach it, and my big probe 
simultaneously to a vacuum tube CW Tesla coil.  Once I have 
determined that I have exactly 100 kV on the big probe I can measure 
my instrument output at the bottom and determine my calibration 
number.  Whenever I read five times this value, I will know that I 
have 500 kV on top, and so on.

I have a copy of the Breit, Tuve and Dahl paper mentioned.  They used 
a capacitive pickup probe inside the oil filled housing at one end 
where it would pick up fractional voltage from one end of a fully 
isolated 1/2 wave secondary.  The other end of the secondary was 
connected to dick, zilch, nada. The only way the far end of the 
secondary could return current for the capacitive voltage measurement 
loop was through some very small capacitive coupling back to the containment 
vessel through the oil.  I am not convinced that these fellows 
arrived at true voltage claims as I am unable to see how they 
might have calibrated their probe to any degree of accuracy.  If 
their coil had been a grounded 1/4 wave helical resonator with only a 
single oil filled space from the hot terminal to the divider pickup, I would 
have much more faith in their claim as it would have been possible to 
calibrate their coupling medium accurately at lower voltages from an 
outboard power supply that could have itself  been calibrated directly by the 
sphere gap measurement technique.

It is a good thing that most of us here on this list don't require to 
know exactly, or even approximately what the output voltage of our 
coils is.  All we care about, and reasonably so, is spark length.  
Like most _guy_ things, this is just another one where bigger IS 
BETTER!  


rwstephens