On Saturday 01 August 2020 14:37:49 Matthew Herd wrote: > Thanks Gene, I hope you’re well also. I disconnected that grounding > wire, no difference observed in the ppmc.0.encoder.03.index behavior. > The noise seems the same both when spindle is running and stopped, > with a tendency strongly toward "true" than "false." Pulses seem to > be both long and short, but I’d guess they’re about 80-90% true. Not > at all what I’d expect, even with noise. > > Matt > Then keep disconnecting grounds, looking for those that are grounded when the obvious connection is removed. You want that connection to the common bolt, you don't want it anywhere else.
Using the scope, ground the scope probes ground lead to that bolt, no other connection, no matter how handy it may be, will give you valid results. If the scope is AC powered, put one of those usually grey 3 to 2 adapters on its power cord. You want that bolt to be the only ground the scope see's. Put a 2' clip lead extension on the probes ground lead if you have to. You will see more noise but you'll also recognize the noise pattern so your eyes can visually subtract it, knowing that noise is the long ground lead. I found on one of my machines several years ago now, that a 3 foot length of 3/8" wide flat braid, covered to prevent its touching the control box as it was leaving, and screwed solidly to the nearest point of the machine frame was a huge help, but I was slow, I had to blow the probe input of a card before I grokked that the machines frame was not grounded. Disconnected, the machine had 150+ volts of noise exceeding the scopes sub 10 ns rise time anyplace I hit with a probe. That was an eye opener for sure, so now they all sport that hunk of braided copper. And obviously other grounds are hunted down and eliminated. I'm nearly all steppers but I use shielded cable to the motors with the shield grabbing that bolt, but the shielding stops in one of the smallest Hammond die cast boxes epoxied to the side of the motor, taped up so it can't touch the box. All of my tally switches get their ground reference from that single bolt. And now it all Just Works. ;-) > > On Aug 1, 2020, at 1:19 PM, Gene Heskett <ghesk...@shentel.net> > > wrote: > > > > On Saturday 01 August 2020 12:10:55 Matthew Herd wrote: > >> I'm still having issues with the rigid tapping. It works sometimes > >> and fails other times. After scoping the motion.spindle-revs, it > >> appears to be consistent with what we would expect aside from one > >> possible issue. The spindle revs reset to zero upon G33.1 being > >> called, then count up until they stop, reverse, go negative past > >> zero, then return to clockwise motion. However, on the second zero > >> crossing (going positive) the revs go positive, only to be reset to > >> zero momentarily thereafter. I'm not sure if this is normal > >> behavior or not. > >> > >> However, what isn't normal behavior is that the > >> ppmc.0.encoder.03.index value is loaded with noise. Not occasional > >> noise, but constantly triggering in irregular intervals regardless > >> of whether the spindle is turning. I'm baffled as to how this > >> could be so noisy and was wondering where you might look next. > >> Grounds look fine aside from the fact that the control cabinet and > >> the power cabinet have a ground wire connecting them in addition to > >> being grounded through the machine. > > > > That quite likely is the problem. Thats a ground loop. Ground > > things only at a single bolt in the control cabinet, and remove any > > machine grounds at the encoder end of the wiring. Ground loops are > > only good for acting as antennas to pick up noise. And in a machine > > full of motors which are regulating motor currants by switching on > > and off to hold the average you or the driver has set, there is 50 > > to 175 volts of noise free for the asking. To ground the machine, > > connect the third, static ground wire in its AC power cord to this > > bolt. If more than one power supply, arrange the cordage to come > > thru a single power strip, with only one of the individual cord > > grounds completed to that bolt. Ground the switcher supplies earth > > terminals to that bolt, and if needed, the - terminals of all those > > supplies to this bolt. You may need a long bolt, thats ok. > > > >> When removed from the USC board, the > >> index can be measured with a multimeter as the spindle is rotated. > > > > If reading to machine ground, thats bad, If reading to logic ground, > > thats good. Logic ground can be connected to that single grounded > > bolt but the distribution of that ground should resemble a star, and > > any ground wire lifted off that bolt should not have continuity to > > ground anyplace else. > > > > This is also good to protect the electronics in that machine from > > nearby lightning strikes. That way, the lightning strike may bounce > > the machine a hundred thousand volts, but its all in unison and the > > 3.3 volt logic doesn't see it or get damaged by it unless there is a > > large capacitance to earth ground to unbalance that bounce. Thats > > generally unavoidable when several ton of iron is sitting on a > > concrete floor. But although the pole that serves this house gets > > tapped occasionally, I have not lost any electronics to those > > strikes in several years since I brought the grandfathered in since > > the early 70's, pre NEC service up to code in 2008 as I was building > > the garage. The power folks haven't been so lucky, they lost a 25kw > > can once. It might have been an askerol filled can which is a time > > bomb after 20 years or less anyway, but I think they hung a 50kw > > full of Crisco in place of it. Outdoors, Crisco is legal, but the > > PCB's are fireproof. > > > >> I > >> forgot to bring my scope to the shop today (I didn't think I'd need > >> it) so I can't scope anything until tomorrow. Is it possible > >> there's a pull-up resistor missing? > > > > There might be. I am not using any except the normal pullups in the > > logic that give a true on the halmeter when no input is connected. > > Mesa cards generally have adequate pullups without external helpers. > > Sainsmart bob's don't generally need them either. > > > >> Thanks, > >> Matt > > > > I hope this helps Matt, stay safe and well now. > > > > > > 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) > > If we desire respect for the law, we must first make the law > > respectable. - Louis D. Brandeis > > Genes Web page <http://geneslinuxbox.net:6309/gene > > <http://geneslinuxbox.net:6309/gene>> > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > <mailto:Emc-users@lists.sourceforge.net> > > https://lists.sourceforge.net/lists/listinfo/emc-users > > <https://lists.sourceforge.net/lists/listinfo/emc-users> > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
