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Re: grounds, measurement

Good Post!!

Tesla List wrote:
> 
> >From pierson-at-msd26.enet.dec-dot-comThu Nov 14 22:21:49 1996
> Date: Thu, 14 Nov 96 20:14:51 EST
> From: pierson-at-msd26.enet.dec-dot-com
> To: mail11:  ;
> Cc: pierson-at-msd26.enet.dec-dot-com
> Subject: grounds, measurement
> 
<SNIP>
> 
> They do the measurements at 60Hz, or DC.  [i'll 'handwave' about this
> below]  They reccomend using realtively high currents, to avoid stray effects
> from stray currents, and to emulate operational conditions.  The preferred
> method is to use an isolation (1-1) transfomer from the power line.
> 
>         CAUTION:  YOU CAN KILL YOURSELF THIS WAY!
> 
>                 Enuf Said?
> 
> Suitably fuse and instrument the secondary side.  Measure E and I (both AC)
> simultaneously while driving current from the ground under test to the
> reference ground.
> 
> If no ground reference (eg water pipe) available:
>         minimum of three electrodes needed.
>         Denote one as "R" (the one to be measured)
>         Two random grounded things, at some distance (not specified.), call them
>         A and B.
>         Using technique above, measure all three resistances:
>         R to A  r1
>         R to B  r2
>         A to B  r3
> 
>         Rground = ((r1+r2)-r3)/2
> 
> They discuss essentially similar methods of measuring ground with bridges or
> ohmeters, the technique is the same, tho the use of 10-12v or so, minimum,
> to avoid odd insulating effects of low voltages.  (ferinstance, i would
> NOT use any common ohmeter...)

Ever try using an analog ohmmeter?? The low voltage combined with
galvanic action and electrode polatization results in an initially low
reading that slowly rises to a significantly higher value (2-3X).
Reversing the leads does the same thing again, only with the initial
reading now being significantly lower. Its almost like looking at the
resistance of a very leaky electrolytic as its being charged by the
voltage coming off the meter! 60 Hz AC works much better!

> 
> They never come right out and say what a 'good ground' is, numerically.
> The EXAMPLES (measured) tend to run between 30 and 60 ohms.  (this implies
> an amp or more if 110vac is used.
> 
> They include a curve of resistance vs temperature that matches the figures
> from the other reference, more or less.(No freezing, 78-32 ohms range.)  The
> relavance is that the ground WILL change if the ground freezes and will change
> again if a coil starts pushing amps into it, heating it.
> 
> Speculation 1)
> It might be interesting to do this WITH RF, say, coupled off the primary, down
> to some manageble voltage.  I some nice test equipment discussed here, the
> proper shunts and voltmeters should allow characterization of 'ground' AT
> OPERATING FREQUENCIES.   (or do it with a signal generator.  less fun....)
> 
This sounds like something that could be done fairly easily with a
higher power CW tube or solid state coil. This certainly could give a
more accurate view of the entire grounding system including the wire
from the resonator base to the ground rod(s). I'm going to give this a
try with my signal generator (if its got enough oomph!)

> Speculation 2)
> Somewhat ad rem the thread on ball lightning.
> (I saw the Corum's presentation on this at ITS Con in '90(?)
> They tried for BL from Bill Wysock's coil, i left somewhat early, i am told
> they 'may' have gotten some later.)
> 
> Anyway, my point about base current, firstly WHICH base current, when?
>         With the coil running, but not broken out?
> (As Tesla may have planned on operating)
>         OR with sparks flung about?
> 
> First case:
>         I submit that base currents will be HIGH.  If the secondary is
>         running as a resonant 1/4 wave, it has a voltage PEAK at the top and
>         a current peak at the bottom.  There is current multiplication at the
>         base even as there is a voltage multiplication at the top.
> 

Good point! Larger coils can easily have 10's of amps of RF (or more!)
with NO breakout - the lower the secondary L, the higher the current at
a given power level. 

> Second case:
>         Broken out.  hmmmm  I'm unclear here.  Likely things change.  I've
>         seen 'series resonant at 10-20 MHz' proposed/measured...   hmmmm again.
>         Suppose its parallel resonant, with the loop closed by the spark?
>         That means spark current (large) returning by way of the ground
>         connection, with the secondary/electrode/arc, as the whole is a
>         paralle (tank) circuit with large circulating currents.  Handwaving.
>         I could easily be wrong.
> 
I'd suspect it depends very strongly upon the nature of the breakout.
Streamers to air are a much different animal than strikes to a grounded
object. Just looking at the change in secondary Q before and after
streamer breakout, there's certinly very strong evidence that we still
have a series LC circuit, and still get resonant rise, but with much
lower effective Q than before breakout. An arcover to a grounded object
makes the secondary Q go to ZIP, as any stored secondary energy is
_very_ rapidly removed.

It sure would be neat to get a more direct way to measure streamer
currents to air - at full cook, mine easily light a 25 watt bulb to
almost full brilliance...

>         regards
>         dwp


Safe coilin' to ya!

-- Bert --