Mike Jenkins (mikejenkins@VNET.IBM.COM)
Mon, 4 Mar 96 09:51:02 PST
Regarding the "ground bounce" observed by connecting both 'scope probe
tip and ground to the same point, I believe it is due to inducing a
current into the probe ground lead and out the 'scope's power cord
ground. I have seen >10 volts on a 'scope channel shorted to ground
when a big lab power supply was turned on, causing a DC drop in the
ground loop: outlet gnd<->scope<->circuit board<->power supply<->
outlet gnd. The voltage seen is clearly not any voltage at the
shorted probe tip, but simply how the scope channel responds to
current forced thru its probe ground into its frame ground.
Hope this helps. Good luck.