RE: Differential voltage probes 3

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

Original poster: "Steven Ward by way of Terry Fritz <teslalist-at-qwest-dot-net>" <srward16-at-hotmail-dot-com>

Hey Terry,

I know very little about the technology that we use for measurements, but i 
can already see how this simple probe will be well worth the $45 to put it 
together!  Ok, so its super fast and clean, and can take up to what, 10kv?
Is it possible to go for 20 or 30kv ratings by seriesing more of these SMT 
resistors?  How much bandwidth would you loose?  Im alreade getting sick of 
my plain old probes, i want something that will be able to measure into the 
kv without me blowing any more channels on my scope!  And wow, they put it 
all in a singe 8(assuming from the diagram) pin chip?  Cant beat that, 
though you better make sure your soldering skills are up to par before you 
go and solder that one on.  $9 is a bit steep.

Ok, so excuse my ignorance, but how is this probe going to be packaged?
Will there be a little box tha plugs into the scope, and then a shielded 
cable with your 2 tips?  Will this cable mud things up?

Well, it sounds cool!  When its all done in working, im sure at least a few 
people would like to buy one.  I bet you could make a bunch of printed 
boards that size for not too much money.  What do you think a final cost 
may be?  $60?  i guess you need a box and some cable, the cost of the PCB.

I dont have to tell you to let us know how your first setup goes!

Steve Ward


>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: RE: Differential voltage probes 3
>Date: Sat, 28 Jun 2003 19:46:25 -0600
>
>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>Hi,
>
>Ok, using bleeding edge, oh!, I mean leading edge parts...  I got it back 
>down to one IC.
>
>http://hot-streamer-dot-com/temp/DiffProbe21.gif
>
>The fabulous Ti THS4151ID apparently does all the power supply offsets and 
>CMRR fixing internally.  That chip is basically the whole enchaladia!   So 
>I just added Ohmite's little 5kV resistors, some 1% 1K resistors, some big 
>NPO caps and it's done.  It would almost fit on a quarter ;-)
>
>There are some relatively expensive parts now, but the total cost is not 
>that much.  The input resistors are $4 each, the IC is $9, the NPO caps 
>are $2...  But I think the total cost would be about $45.  Yes, it is all 
>that little surface mount stuff and you have to be careful since the high 
>voltage is very near.  Probably a good candidate for HV conformal coating...
>
>The input resistors are 5%, but hopefully they are somewhat matched as 
>they come off the reel.  The PCB around those resistors would have to be 
>routed out to insure voltage standoff.
>
>I have no idea what the frequency response would be, but it "should" be 
>pretty darn high!  The IC is 150MHz and I am feeding it just like it 
>wants.  With the input resistors being so small, a LOT of response 
>problems just vanish.  Caps across the 1k resistors could limit the 
>frequency response if needed.
>
>Unless someone has a better idea, I think I will give this one a try.
>
>Cheers,
>
>         Terry
>