RE: differential probes

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

Original poster: "FRITZ, TERRY by way of Terry Fritz <teslalist-at-qwest-dot-net>" <TERRYF-at-aei-dot-com>

Hi Jimmy,

I quickly looked it over and had these thoughts:

Out 1 and 2 are connected to the ground legs of the BNC connectors.  They
should go the the center pins of the scope connectors.

Holes for LED31 and B31 and B32 wires may need to be larger?  Hard for me to
judge from the pictures...

C12 and C21 should all have their "own" vias going to the ground plane (high
current at 150MHz!).

There should be three "very" separate grounds.

	The low voltage electronics will have it's own ground plane but that
will end on the low voltage side of the 1Meg resistors.  There should be
"no" ground plans under the HV resistor areas.  The HV resistors from a very
wide line of isolation separating the low voltage stuff from the high
voltage stuff.  Only the resistors should cross that line.  The grounds are
also "very" separate since under a fault they will be far from zero volts!

	The MOV sets each have their own "very high" current (like 2000 amp
pulse) grounds that go out to ground studs.  The MOV grounds are meant to
take giant faults and ground them separately away from the other grounds.

The Official "CE" clearances for 2000Vp on a PCB are 1 inch!
"Theoretically", the high voltage side stuff should all be spaced 1 inch
apart from anything else.  2000V will easily arc 1/4 inch between sharp
points over a surface.  So you may need far more spacing on the high voltage
stuff.

Not sure BNC connectors are good for the high voltage.  They make HV BNC 
connectors but they are super expensive.  I was going to go to
the HV fuses (yet to be figured out) and then to banana jacks.  In one way,
I like the BNC and coax cables since they "could fail" and stop a high
voltage event from getting through to the scope.  Sort of a "crowbar" ;-))
However, we should probably try to stop over voltage events more
diplomatically :o))  I did find some 15kV 5 amps fuses but they are 18 
inches long!

http://www.ferrazshawmut-dot-com/products/pdf_107/15.5%20kV%20CS-3.pdf

Might have to start thinking about Ken's idea of hard clamping and hoping 
something else blows up first...

Cheers,

	Terry




-----Original Message-----
From: jimmy hynes by way of Terry Fritz <teslalist-at-qwest-dot-net>
[mailto:chunkyboy86-at-yahoo-dot-com]
Sent: Tuesday, July 15, 2003 8:27 AM
To: tesla-at-pupman-dot-com
Cc: terry.fritz-at-aei-dot-com
Subject: Re: differential probes


Hello,

The PCB file is on my site
<http://www.hot-streamer-dot-com/chunkyboy86/diffprb.pcb>www.hot-streamer-dot-com/ch
unkyboy86/diffprb.pcb

There are also some pictures of it
<http://www.hot-streamer-dot-com/chunkyboy86/diffprb.jpg>www.hot-streamer-dot-com/ch
unkyboy86/diffprb.jpg
www.hot-streamer-dot-com/chunkyboy86/diffprb2.pcb

Someone should probably check it for errors, and either tell me about it or
fix it and give me the new file.

One thing that worries me is the BNC connectors. There could be up to 3600
volts across the pins, and it doesn't look like it can take it. Should both
connectors be female, and just plug it into the scope through an extension?
It seems like the only way to do it with two channels

I changed the switch slightly, the one I was planning on getting will fit
in the circuit board, or it can be connected the way Terry was planning. If
everything looks ok, I'll order some boards and parts tomorrow afternoon.


--- Tesla list <tesla-at-pupman-dot-com> wrote:
  > Original poster: "jimmy hynes by way of Terry Fritz
  > <teslalist-at-qwest-dot-net>" <chunkyboy86-at-yahoo-dot-com>
  >
  > Hey everyone,
  >
  > I'll lay it all out tomorrow so you guys can check
  > it.
  > With the surface mount chips, it is probably better
  > to
  > skip the prototype and go straight to the PCB,
  > agree?
  > The PCB has a two day turnaround, so I can probably
  > get them built by the end of the week. Who wants to
  > try one?
  >
  >
  > --- Tesla list <tesla-at-pupman-dot-com> wrote:
  > > Original poster: "Terry Fritz"
  > <teslalist-at-qwest-dot-net>
  > >
  > > Hi Ken,
  > >
  > > At 09:53 PM 7/13/2003 -0500, you wrote:
  > > >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
  > > >................