Re: HV probe for primary measurements

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

Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>


At 01:53 PM 28/09/02 -0600, you wrote:
>
> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Fri, 27 Sep 2002 12:20:14 -0600
> To: tesla-at-pupman-dot-com
> Subject: HV probe for primary measurements
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Fri, 27 Sep 2002 12:39:52 -0600
> 
> Original poster: "Gregory Peters by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <s371034-at-student.uq.edu.au>
> 
> Hello TCML,
> 
> I would like to use my CRO to examine the waveforms in my primary
> circuit during operation.  Can someone point me in the direction
> of some suitable schematics for either a HV probe or some kind of
> current transformer metering device? I saw Terry's setup using the
> optocouplers but I can't find any schematics or theory of operation.
> Can I just use a big string of resistors?  The idea of directly
> measuring the primary voltages and currents, quite frankly, scares
> the utter crap out of me, but I am determined to investigate them.
> I will NOT be touching the CRO during operation as a result.
> I just don't want to go anywhere near it.
> 
> What about making a current transformer by winding some wire around
> a ferrite core?
> 
> Cheers, Greg.
> 
Hello Gregg, Coilers,

I wanted to do something similar, but in the ground lead of my secondary.
What I constructed was a radio frequency current transformer, by winding
16 turns of teflon insulated hookup wire onto an Amidon T-200-2 toroid
core, and passing the secondary ground wire through the toroid hole to
yield a turns ratio of 1:16 which gives a nice level of signal.

A length of RG-58U coaxial cable brings the sensed signal to a point far
removed from the coil where it is terminated with a 50 ohm, 5 watt, non-
inductive resistor.  I use my lab VTVM and its RF probe to measure the
voltage developed across the resistor.  In your case, you would simply
connect your scope across the terminating resistor.  You could also do
a bit of "on line" measuring by simply rectifying the voltage developed
across the resistor and using a multi-meter to measure the relative
power...handy for optimising the tuning, etc.



73, Weazle, VE3EAR/VE3WZL
G-1#1214

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  http://www.hurontel.on.ca/~weazle