Re: electrical noise

One good thing happened. I switched the ports between the 2 servo
motors and discovered that the parallel port pins 3 and 7 were not
generating a signal. With a new parallel port installed at least the
motor is turning again but the noise problem persists. I already went
through a keyboard generating random keystrokes. The failure of a
parallel port and a keyboard seems very unusual to me. I just wish I
could figure out what is causing the ground loop.



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "toolspindoctor"
<clarkfamily5@...> wrote:

>
> 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.
> >
>