Re: differential probes

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Or, a Sidactor (they're used in transient suppressors for cable TV.. about
50 pF capacitance in the "off state" then you put a parallel pair of back to
back small signal diodes in series to get the C down real low.

Check Teccor's website for lots of details.. these look like the hot
ticket..
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, July 13, 2003 7:57 PM
Subject: Re: differential probes


 > Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<tesla-at-lists.symmetric-dot-net>
 >
 > On Sun, 13 Jul 2003, Tesla list wrote:
 >
 >  > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >  >
 >  > Hi Jimmy, Finn, and All,
 >  >
 >  > This is the present schematic and parts list I have in mind for the
 >  > differential probe.  I have NOT assembled or tested it yet!
 >  >
 >  > http://hot-streamer-dot-com/temp/DiffProbe-5.gif
 >  >
 >  > http://hot-streamer-dot-com/temp/DiffProbe-5p.gif
 >  >
 >  > It is still just using the basic 150MHz TI  THS4151ID differential
 >  > amplifier IC and other straight forward parts.
 >  >
 >  > One thing I am "trying" to add is a front end that can take a hard hit.
I
 >  > will have a system ground stud and MOVs at 1800 volts each.  These will
be
 >  > fused with low current but high voltage fuses.  The idea is if you get
a
 >  > say 20,000 volt cap on the input, the MOVs will clamp it and the fuses
will
 >
 > How about some neon lamps or one of those glass or ceramic tubes the size
 > of a pencil eraser with metal leads? Both should have a low capacitance,
 > and don't conduct until 70 volts or so for neon, and several thousand for
 > the larger ones. Maybe put them both in parallel. You probably want the
 > lowest possible impedance in a short mode, otherwise the probe or what's
 > left of it will dissipate lots of heat, which leads to it blowing up or
 > catching on fire. Large energy storage caps are designed this way- to
 > short out with the lowest impedance so their energy is dissipated outside
 > the cap tank in bussbar and fuses, not inside where the tank will build up
 > pressure and rupture. MOVs are basically firestarting kits.
 >
 > KEN
 >
 >  > break the circuit away without damaging anything like the scope.  Since
we
 >  > play with big voltage stuff, I think super protection like this is a
real
 >  > good idea to have.
 >  >
 >  > So that's were I am at the moment on this...
 >  >
 >  > Cheers,
 >  >
 >  > Terry
 >  >
 >  >
 >  >
 >
 >