> > I should probably start a new thread here but there is definitely a > > similarity in the noise problem. > > > > In my jet 9 x 20 conversion I was getting lots of noise spikes on my > > spindle encoder feedback to the 7i78 card. > > I went through all the regular suspects, grounding, shielding twisted > > pair etc. with little or no change. > > On a "real" scope I was watching the noise spikes as vertical lines > > superimposed on the encoder A and B square waves. The noise was there > > even if the spindle was NOT turning and when the spindle motor > > controller was OFF. > > > > I started turning off things to see if the noise was from an external > > source such as the monitor or computer's switching supply. > > I even disconnected the DB-25 to the computer and supplied the 7i78 > > from a linear supply.....No change. > > > > Then I wondered what would happen if I turned off the G320 servo > > drives. I pulled the error/reset connections on the G320's and the > > noise went away. > > When I hooked the error/reset lines back up to one of the G320's and > > decreased the horizontal sweep on the scope to 10 microsec per > > division I got a beautiful rock solid 2 volt burst recurring every 50 > > microseconds and ringing for about 10 microseconds. > > > > My noise source is the G320's PWM generator which switches at 20 khz. > > > > I'm still not sure how such a horrible noise signal gets from the 48 > > volt motor armature switching circuit in the G320 to the input of the > > 7i78 but at least now I know the source and can try to fix it. I'm > > pretty sure that I can't just put a cap across the armature outputs > > of the G320 because that does bad things to the H bridge. > > > > Has anyone else experienced the PWM switching noise of their drives > > getting into their signal level circuits? > > If so, how did you deal with it? > > > > Thanks, > > Cecil > > > Ahh, so I have company. I've converted the switching motor psu's to > analog, but its pretty hard to block when the rediated noise is 12 volts > p-p at about 100 megahertz before you start building a star ground.
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