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For David L. Jones, 'grounded probe' bounce

T

Tim Williams

Soak your eyes on this one:
http://webpages.charter.net/dawill/Images/Photoflash_Discharge1.jpg

Circuit values: 20uF at 400V, discharging through xenon horseshoe tube.
Probe shorted to its ground lead, laying nearby on the bench.

The remarkable part is this is actually my analog scope. No storage
involved, just a Tek 475. Or actually, as a friend put it, "storage camera
;)", since it was a 10 second exposure.

Tim
 
D

David L. Jones

Tim said:
Soak your eyes on this one:
http://webpages.charter.net/dawill/Images/Photoflash_Discharge1.jpg

Circuit values: 20uF at 400V, discharging through xenon horseshoe
tube. Probe shorted to its ground lead, laying nearby on the bench.

The remarkable part is this is actually my analog scope. No storage
involved, just a Tek 475. Or actually, as a friend put it, "storage
camera ;)", since it was a 10 second exposure.

Tim

I like it!
What's the V/div?
Is it reproducable with a proper al-foil short?
How about 50ohm terminated coax?
How about no probe cable at all?

Dave.
 
T

Tim Williams

David L. Jones said:
I like it!
What's the V/div?
Is it reproducable with a proper al-foil short?
How about 50ohm terminated coax?
How about no probe cable at all?

I think it was 50mV/div (0.5V/div with the 10x probe), but since it's
sensing uncalibrated current, that doesn't tell much.

The probe has to be pretty close to get a strong signal (I had it right over
the capacitor), otherwise the probe picks up too much noise from the
breadboarded(!) switching supply (a 400V, 30mA supply has to switch a lot of
winding capacitance..).

Surprisingly, I got a similar pulse from a snap-in electrolytic. Those
things are fast!

Tim
 
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