Re: Ragowski(sp?) coils

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>

Hi Bert, Terry, All

Richard wound a home brew Rogowski Coil (RC) on 3/8 PE tubing ("polyflow") like
a typical close wound resonator, then bent back on itself and epoxied into a
solid 1/4" to close coil.  From what I've read, to de-Q a RC, you have to
tap the
coil and place non inductive swamping resistors in parallel across the coil
segments.
The advantage of this is the Rload is automatically built around the coil.
Total resistance of series RL parallel segments can be anything you want,
but IMO
I'd shoot for 50 ohms, since that is a standard input impedance for just about
all instrumentation.

To calibrate, you need a low impedance power signal generator driving into a
resistive load, sine wave AC power up to perhaps 500kHz.  A multiplier and
offset
term can be developed (2 point calibration).  While used in conjunction of
water arc
explosion work, typical accuracy's was better then 10%, and much better is
possible with good calibration/measurement techniques and equipment.  Currents
up to 14 kA peak at 16-18kVDC was measured successfully, and when back
calculated to Zsurge and charge voltage, calculated peak currents agreed with
calibrated measured values from RC within 5-10%.

In closing, the advantages of an RC are:
1.  Diameter can be made size commensurate with hold off voltage requirements
     Diameter of unit mentioned above was about 8-10" if my memory is correct.
2.  Capable if measuring extremely high currents (mega-amperes)
3.  Wide bandwidth (depending on construction 100 MHz or more)
4.  Relatively inexpensive to make
5.  Only real difficulty is fabrication and calibration, this is the cost
factor in commercial
     units..

Happy New Year All!

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA

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