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Making a differential scope probe, how tough?

J

Joerg

Jan 1, 1970
0
Hello Stanislaw,
Nothing to do with measuring the signal and CMRR. Safety = 50 uA (
that's my keyboard spelling micro) at line frequency can (does NOT have
to ) throw the heart into pachanga dance (medically called fibrillation).

Yep, been designing med stuff since the mid 80's. We kept it under 10uA
because you have to go with the "least common denominator" between
countries' regs. Reason I mentioned it is because it does help with
CMRR, big time.

This part of medical electronics many times IS the major time consuming
part of designing an intensive care room equipment.
There are NO excuses.

After a while you get a good feel which parts you can use and which
companies are the most supportive in obtaining the docs for the design
history file and ECO. The problem is insulated wire for magnetics since
it needs to be tested and certified per running foot. Every once in a
while a supplier drops away and clearing a new one requires quite some time.

As to no excuses, I go one step farther than IEC601 goes (or used to
go). Even for stuff that doesn't have to be defibrillator proof I insist
on designing it that way. Else I would turn down the project. Even more
so after seeing how over-worked and tired physicians can be. That's when
even the most robust person can make mistakes.
 
N

Nico Coesel

Jan 1, 1970
0
Paul Mathews said:
Are you wanting high voltage differential probe or logic level diff
probe...2 very different animals. Assuming the former, it's not too
difficult to do something like Tek 5200. You attenuate both inputs with
matched resistors to get the voltages down to reasonable values,
connect to an instrumentation amplifier and a line driver. Tek 5200
uses readily available Intersil ICs, if I recall correctly.
Paul Mathews

Didn't Elektor publish such a circuit several years ago?
 
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