Re: Primary Scoping
Subject: Re: Primary Scoping
From: jim.fosse-at-bdt-dot-com (jim fosse)
Date: Tue, 27 Feb 96 00:08 PST
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> I was woundering if anybody had hooked a high voltage divider up to
>the primary of a TC and observed the waveform, measured the spark gap quench
>time or performed any other measurements? I've got an 20KV RF rated voltage
>divider and a dozen or so Dale HV-2 100Mohm resistors. Any thoughts on
>safety? I'm a degreed EE but haven't done any HV work and want to make sure
>I'm safe before I'm sorry.
>I have thought about using a 1000:1 divider ratio using 4 of the dale
>100Megohm resistors in series to a 5 parallel combination of 2megohm carbon
>comp resistors. I'll then put some transorbs to ground before the scope
>connection. All components will be physically well mounted to prevent
>BTW, transorbs can be thought of as a 5ps.(thats not a typo: 5*10^-12
>second) zener with a many thousand Amp ratting. By using 2 of the
>unidirectional devices in antiparallel I can get any clamp voltage between 5
>and 500 volts with only a 200pF capacitance penality.
>I still have to reduce my common mode power line noise, it's getting into
>the scope with the scope input switch on ground and no probe cable
>connected. I do have 1 heavy duty line filter in series with the neon.
>Any thoughts, physical barriers, components?
Last night I solved the common mode line noise by seperating the RF ground
from the line ground with a 550uH inductor. I can't see the spark any more
on my scope, with the input grounded. I then added a 12" antennae to the
scope input and measured: 2.5V peak on the second positive peak, 1Vpeak on
the 9th positive peak. I saw about 5 pulses from my spark gap per 60Hz half
When I put the secondary in place, the input signal went to about 10V peak
and was still ringing down when the next spark occured.
It doesn't seem that a direct connection has to be made. A short antennea
works well and provides a great isolation barrier!