Having fought encoder noise first with US Digital and then some sort of encoder/motor issue with an out of spec motor into HP_UHU drives I do sympathise with the issue you are having.
Think of the problem this way. A noise spike to be detected has to create 4.5V into the 74HC4050 level translator. Say the input resistance of the device is 1Mohm; 4.5V / 1,000,000 is 4.5uA. The voltage drop across your 1K resistor is 0.0045V which is low enough to ignore so pretty well all of the 4.5V noise shows up as an extra index pulse. Now assume the energy of the noise is only just enough to generate that 4.5uA. If instead your load resistor is 470 Ohm then 470 * 0.0000045A = 0.002115V. Hardly enough to show up as a voltage blip much less an index pulse. Buy some of the clamp on ferrites too. Something like this. https://www.istockphoto.com/photo/lan-cable-with-ferrite-clamp-or-clamp-filter-gm695515764-128583117 John > -----Original Message----- > From: Peter Hodgson [mailto:peterjohnhodg...@gmail.com] > Sent: October-11-21 2:33 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Fwd: Rogue Index Pulses > > Thanks all for your continued support. > > connected directly to AC earth wire from the 240v outlet. I�ve also made a > polycarbonate mounting bracket for the encoder housing > so it�s insulated from the machine frame and terminated it�s screen to the > same earth star bolt at the control panel end. > > I�m happy to have this now as best practice but it wasn�t the solution for > the ghost pulses. > > Interestingly, I noticed that the earth cable coming from the spindle VFD > screen made the encoder signal extremely noisy when it > was in close proximity to the encoder cable. Also, just for your info, the > stepper motors or drivers create a lot of �white noise� on > the shop radio when they are holding or running so I guess they are chucking > out a lot of high frequency noise. > > It seems I have three options from here. > > 1) Change to the HPCL2631 opto isolators. > > 2) Change to the 74HC14 buffer. I think I will need resistance dividers with > this as the max input in the datasheet suggests 6v so I will > need to drop the 12v encoder signal to <6v (?) > > 3) Try the existing 74HC4050 buffer with resistance dividers. > > I�ve got some components on order so I guess whichever turns up first will be > the first I�ll try. > > Seems like I also need to find myself some sort of oscilloscope on eBay! > > I�ll keep you posted. > > Cheers, > > Pete > > > On 11 Oct 2021, at 21:11, Gene Heskett <ghesk...@shentel.net> wrote: > > > > ?On Monday 11 October 2021 15:49:43 Chris Albertson wrote: > > > >> You could be correct. High impedance is a recipe for noise. > >> I had suggested a resistive divider just because it is simpler. But > >> you are right about providing a ground path. A divider certainly > >> would do that. If an opto is really needed then use a high-value > >> resistor to ground to keep the line from floating and bleed off > >> static. > >> I also don't like the idea of grounding the shield on the encoder end > >> as it makes it impossible to know the path from encoder housing back > >> to true Earth ground. It is "unanalyzable" (if such a word exists) > >> Running the shield to star ground point makes it easy to verify it is > >> correct. > > > > +100 Chris. Run a separate ground to the encoder from the star bolt, and > > connect the cables overall shield ONLY to that bolt. If that encoder > > uses the shield as its ground connection, toss it in the out bin, and > > get one that does have a separate ground wie going into it which is > > isolated from the metalic case. I would also verify that the encoder has > > a good ground to its metalic housing. Painted brackets are a recipe for > > failure. As are metallic shaft couplers. The elastomeric coupler that > > came with my omron, failed a year ago, and the coupling is now a couple > > layers of heat shrink with the inside layer of thermal glue. If it > > fails, replace it with a fresh copy. 50 cents maybe. > > > > 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, 1940) > > 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 > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > 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
