On Saturday 14 January 2017 12:00:37 Cecil Thomas wrote: > 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.
They will take a few days to get here, but I've ordered an assortment of ferrite split bead chokes in hopes I can block some of that longitudinal noise. And of course I'll advise the list as to what they do when I've had a few hours to play after they arrive. So as they used to say on the radio when we wuz kids, stay tuned. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today. http://sdm.link/xeonphi _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
