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Re: ScopingSSTC

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>


Another way to isolate your scope is as follows:

Take a 5-10 Amp variac core with coil.  Put 120 VAC across this winding.
Take 7-8 turns of HV cable (stripped coax works great) and wrap around this first core. Next, wrap another 7-8 turns around a second 5-10 Amp variac core. These are connected together, and, if you do it right, you only need to solder and insulate one connection (by using a longer stripped coax cable). Set this assembly up high on a plastic insulated stand, 2-3 feet away from ground.
This forms a 1:1 ratio scope isolation xmfr that has very good HV isolation from ground. Be sure to set the scope atop an insulated stand when connecting to the 2nd variac core. You need to "float" this xmfr setup and also the scope. 

Only two wires so there are no neutrals and no ground.
We used this setup for a long time before we got our storage scope and 30 kV HV probe. 

Dr. Resonance




Cause the "neutral" you speak of is really a ground... if you need to
do differential measurements, what I do (as I do not have a
differential probe) is take two scope probes, plug one in to each
channel on a dual trace scope, connect the grounds from the two
probes together, and use one probe for each side of the source you
want to measure. you will also want to set your scope to "additive"
instead of altertnating, or chopping, if your scopes preamp does not
do additive, this will not work.

If you are measuring a signal that is not "floating", i.e. a ground
referenced signal, this is not needed.

(I have a Tek 535A, and a 545A, some of my preamp plugins do this,
some do not, I wish I just had a differential plugin...)

-Rich
On Dec 14, 2005, at 1:44 PM, Tesla list wrote:


Original poster: "Alexander Turkin" <alex_3@xxxxxxx>

Hi everyone!

   I cannot understand the purpose of differential measurment. Why
can't I check the form of the signal by connecting the neutral
probe of the scope to one end of GDT and the other probe to another
eng of GDT?????? I think that it would be OK, because i DON't touch
anything, but the wires of GDT (i mean the secondary winding, of
course)

Thanks.