gregz wrote in

rg:

pfm wrote:
Many advocate the use of an isolating transformer. The oscilloscope
probe and ground are then used like multimeter leads. Tektronix and
others maintain this is a dangerous practice and may result in
cumulative damage to the oscilloscope. Differential probes are one
answer, though quite expensive.

Comments please. Thanks

BobH

I have used differential probes and battery operated scopes. That's
the only thing I would recommend.


Proper practice is to put the Device Under Test on the isolation
transformer,not the scope.
leave the scope grounded.


Unless it's a specific service mans isolation transformer, most every
commercial isolation transformer is NOT isolated from ground. Ground
isolation is often what you after because neutral is tied to ground.
Using complete isolation through a service mans isolation transformer
still passes a low level capacitive ac line connection to the circuit,
and measuring high impedance circuits can throw you off. Using a
battery operated scope still connected to the charger will also pass
capacitive ac line coupling.

Greg


TEK makes (or used to make) special probes/amps that isolate the scope from
the device under test(DUT).
they had one that used fiber optics,and another that actually disconnected
the ground for up to 40V,and monitored the ground potential to reconnect
the ground if the potential went above 40V.

A6902,IIRC.

TEK also makes differential amps that can be used with single ended
scopes,but you need a separate probe power supply if it's not a TDS model
scope.

--
Jim Yanik
jyanik
at
localnet
dot com