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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