RE: A new tuning idea? its a current xfmr !

["Dale Hall" <Dale.Hall-at-trw-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Steve,
What you describe is a Current Transformer and a good choice 
    (and provides some instrument isolation protection)

The TC's Sec current is being sensed in the single turn and
transformed by ratio and Burden, i.e. the value of resistor 
on the higher turns 'monitor' side of the xfmr to develop 

a current proportional to the turns ratio (if properly designed).

In order to work (proper design) a HV current xfmr sensor must:
  have close coupling, as in use a toroidal core but also high voltage
isolation between Pri/Sec
  exhibit low core loss at the frequencies of interest:
     resonant frequency for Secondary viewing (to ~300KHz decreasing for
larger Sec's)
     but it would be nice if it was good at the Spark Discharge frequencies
(to ~5MHz)
     note: higher frequency cores are likely smaller w/finer particles &
maybe exotic ferrite's
  NOT saturate the core (become non-linear)
     most often achieved by cutting a gap in the core 
         (else current observed will not relate proportionally)
  Any amplifier must be linear over range of use, have adequate frequency
response and not saturate
     Viewing very brief pulse of current is demanding on design of sensor,
amplifier characteristics etc

A current xfmr is used to instrument Pri, Sec & Arc currents in my single
shot DCTC 
   oscilloscope picts at http://www.cowmail-dot-net/dalehalldctc/
   implemented via Tektronix commercial oscilloscope probe and amplifier.

Regards, Dale

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, July 21, 2000 4:43 PM
To: tesla-at-pupman-dot-com
Subject: Re: A new tuning idea?
Original poster: "Steve" <Steve-at-g8cyerichmond.freeserve.co.uk> 

How about this as an alternative, it's used by radio hams for monitoring
earth current. Feed the lead through a ferrite ring. Wind a number of turns
of thin wire through the core to form a secondary. Connect a lowish value
resistor across this, and then measure the induced voltage using an analogue
ac voltmeter. I can't remember any values, but in any case it would depend a
lot on your particular coil. i only give this as an idea that might be worth
playing with, come to that I might have a go myself over the next few days.
Steve
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, July 21, 2000 8:04 PM
Subject: Re: A new tuning idea?

> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
> Hi Gary,
>
> The secondary RMS current is around 350mA for a 15/60 coil.  At least it
> is for my big LTR coil but say 100-400mA should cover them all...
>
> John Courture's Tesla Coil Construction Guide describes this exact
> technique on pages 14-5 and 14-6.  He suggests a number 1891 lamp.  The
> resistance of the lamp is non-linear in this high current, low duty cycle
> use so calibration would be tricky but for basic qualitative tuning it
> works.  Perhpas a way could be found to calibrate it with some thought...
>
> I seem to remeber the "first" person to think of this was that guy from
> Croatia :-))
>
> Cheers, Terry
>
> At 08:56 AM 7/21/00 -0400, you wrote:
> >Several months ago I raised the possibility of metering the light output
> >from a fluorescent tube as a means of quantifying the output of a coil for
> >tuning purposes.  I never actually tried this as further thought made me
> >think that varying streamer length and attachment would result in variable
> >E-fields and unstable readings.
> >Now I'm wondering if metering the secondary base current might provide a
> >more stable and indicative reading of "in-tune"-ness.  This might be
> >accomplished simply by inserting a small incandescent bulb in series with
> >the secondary base connection, and again using a photocell and analog ohm
> >meter to indicate the relative base current.  It would probably work best to
> >provide a close target for the streamers so that they are essentially
> >continuous and the same length.
> >
> >Does anyone know what the RMS base current for a medium-sized (15/60 NST
> >powered) coil might be?
> >
> >Regards, Gary Lau  Waltham, MA USA