Re: electrical noise

Still no progress. New powersupply - same problem. Shielded wire and
grounding one end. The Pixie just shuts off and on with a jolt. Now
I could not even run the machine as the problem has worsened by later
in the day yesterday. At this point I feel totally defeated...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <thom@...> wrote:
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "toolspindoctor"
> <clarkfamily5@> wrote:
> >
> > Can someone give me some insight on how to track down a significant
> > noise problem. I have an oscilloscope and voltmeter. I am using the
> > Pixie card with a servo drive. The Pixie seems to be picking up
> > horrible noise. Nothing I do makes a difference other than making it
> > worse.
> >
> > Thanks
> > Keith Clark
> >
> Finding noise with a conventional analog scope is not easy. The
> problem has to do with grounding and the scope itself. By default the
> shield side of the scope probe is connected to the scope chassis which
> is connected to safety ground. When you connect the probe Return line
> (which you have to) you are grounding that point. If it is already
> grounded it's no big deal. If the noise problem is from a grounding
> issue it may get worse or better from the local scope ground. TO see
> the real signal at the point you really need to use a differential
> input probe or have a lot of experience looking at wafeforms and
> understanding what is really there and whst is artifact from the scope
> itself.
>
> If the encoder inputs to the pixie are single ended (the signal is
> referenced to ground) then it's a long antenna for noise. You could
> put your scope on each channel and the waveform should be pretty clean
> when the encoder is sending. Even sitting still the encoder will send
> signals on at least one channel. If it's a differential signal the
> encoder should not be the source of the noise.
>
> THe other potential noise conduit is the Step & Dir in. Once again
> the biggest potential is a shared ground. Just hooking everything up
> to a nearby grounding spot some of which can be some distance apart is
> great for safety but may be a poor conductor of HF noise. I don't
> know enough about the pixie card to know if they have a built in
> cicruit to clean up a funky signal from the PC port. The further
> those two are from each other the more drive you need from the
> computer port. A good buffered BOB might help if the distance is
> greater than a few feet.
>
> It has been my (painful) experience that it's not about a circuit
> being ungrounded as much as HOW/WHERE it's grounded.
>
> Grounding for noise reduction is part science, part voodoo. Ground
> loops are invisible and great noise conduits.
>