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Re: What efficiency?!



Tesla List wrote:
> 
> > Subject: Re: What efficiency?!
> 
> >From hullr-at-whitlock-dot-comFri Nov  8 22:24:32 1996
> Date: Fri, 08 Nov 1996 11:32:11 -0800
> From: Richard Hull <hullr-at-whitlock-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: What efficiency?!
> 
> Tesla List wrote:
> >
> > >From MALCOLM-at-directorate.wnp.ac.nzThu Nov  7 22:25:37 1996
> > Date: Fri, 8 Nov 1996 08:10:36 +1200
> > From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: What efficiency?!
> > Snip
> 
> > I have restored a valve scope for this purpose, but I guess I'm a
> > little too far away to bring it over. Very well, I shall devise
> > something myself. Fair comment. Would you please outline the detail
> > of Rogowski coil construction - I'll check some references today but
> > would appreciate the info anyway.
> >
> > Malcolm
> 
> Malcolm,
> 
> 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.
> 
> I got tired of recal.ing the coils, and purchased a wide band Pearson
> current monitor recently for $900.00 out of pocket. (ouch)  Good
> instruments improve results and reduce hassles.   This is a good one and
> can handle 200,000 amps with a bandwidth of from .5 hz to 4Mhz.  It's the
> cat's pajamas!
> 
> Richard Hull, TCBOR

Richard,

Thanks for a very practical and useful post!! Just what is it that the
Pearson has that one of your Rogowski coils doesn't - what do they do
differently that justifies $900? 

-- Bert --