Re: Differential probes

On Wed, 21 Jun 2006 09:27:19 +0200, "Fred Bartoli"
<fred._canxxxel_this_bartoli@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:


"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> a écrit dans le
message de news:oq7h9298fct69o6683rijcer3ne327somh@xxxxxxxxxx
On 20 Jun 2006 15:53:10 GMT, Jim Yanik <jyanik@xxxxxxxxx> wrote:



We just got a new Tek TPS2024 scope. It's a 4-channel, 200 MHz color
scope and all four channels plus the trigger inputs are isolated. So
you can use regular 1:1 or 10:1 probes for off-ground measurements
at millivolt sensitivity. Slick.

The 50:1 attenuation of the P5205 turns low-level stuff to mush.

John


It won't have the CMRR of a true diff amp.


The TPS2024 is truly isolated to 600 volts RMS

So what? That has nothing to do with differential amp performance.
All that means is the front ends are isolated from the case to 600 V.


That sure sounds differential to me. And it sure lets me measure stuff
that nothing else can.


*almost* differential.
You can surely count on unmatched input impedance.
It'll probably work ok on a low impedance circuit, but try to measure a diff
voltage in a 10K impedance circuit. You might have some surprise.



The only asymmetry in the TPS2024 is the roughly 35 pF from the
channel common to scope ground. That will matter in higher-frequency
situations where the circuit floating common cares, which is unusual.
Most of the time, we are measuring against a fairly stiff "floating
common."

John

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