Re: Ground bounce

mellitz@eagle.ColumbiaSC.NCR.COM
Mon, 4 Mar 1996 15:23:27 -0500

On Mar 4, 9:51am, "Mike Jenkins (8-276-2837)" wrote:
> Subject: Ground bounce
> 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.
>
> Mike Jenkins
>-- End of excerpt from "Mike Jenkins (8-276-2837)"

I've seen this low frequency "noise" alot. FET probes are notorious for
providing sneak ground paths. The other culprit I've seen often is
magnetic coupling.

The first thing I would do is what Don Abernathey suggested. "Draw yourself
a little diagram of the shelf power distribution." Include everything
you can think of e.g. the scope internals, probes, etc.
Don't assume anything is a short or is grounded.

Rich Mellitz, NCR