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Re: What efficiency?!

Tesla List wrote:
> 
> >From MALCOLM-at-directorate.wnp.ac.nzSun Nov 10 21:43:46 1996
> Date: Mon, 11 Nov 1996 10:37:24 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Re: What efficiency?!
> 
> Richard,
>            Thanks for this info (BTW, thanks also for doing the 2-cap
> expt under more rigorous conditions than I employed)....
> 
> > I have made about 20 rogowski coils and all worked OK, but they can be
> > troublesome if you are looking for wideband response.
> >
> > I usually take a piece of tygon tubing about 3/8" in diameter and about
> > 16" long.  I put one end in a lathe and slowly tight wind wire wrap wire,
> > 28 gauge kynar insulation, onto the tubing.
> >
> > The tube is then bent together to form a circle or closed loop.  I put a
> > plasstic plug in the ends to hold them together.  I next get a .01 ohm
> > resistor, carbon only, and shunt the coil out (short it) then I mount the
> > resistor and coil connections to a female BNC jack and place all on a
> > plexiglass frame which has a piece of PVC pipe through the center of the
> > hooped coil.  the wire with the current to be measured is threaded
> > through the pipe and connected.
> >
> > Next I calibrate the coil using a scope a cap and a discharge circuit and
> > figure backwards from the measured ring wave frequency, the L of the
> > discharge circuit, and then the surge impedance sqrt(L/c) from there and
> > then the actual peak current from there.  I try and do this for the
> > frequency near that of what I want to measure.  Note that the Rogowski
> > coil has its own natural frequency too and this will appear as a bunch of
> > trash (mini-ring wave) on the first sine's rise in the damped wave you
> > are measuring. Ignore it.
> >
> > The rogowski is effectively limited as described here to a 1mhz limit.
> > The one for a TC secondary would need to be much bigger.(insulation)  The
> > guys at CEBAF wind their own on hula hoops!! For megamp currents and
> > integrate over time with IC op amp integrators.
> <snip>
> 
> Basically a current transformer. What I envisaged was to place the
> coil around the grounded discharge rod (LV end of things). I had
> trouble imagining why sec. current should be so difficult to measure.
> 
> Malcolm


Malcolm,

If you think that a nice long spark won't come of that grounded rod to a 
small CT, guess again!!  I've seen it happen and have a couple of fried 
front ends to prove it.  Use a hula hoop or a core whose diameter is 
about 1/3rd the length of the spark itself!

Richard Hull, TCBOR