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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