The trouble with guessing that it might be noise on the AC mains power or radiate noise from motor cables or a ground loop is that when you get lucky and the problem stops you never know it is was because by luck you happened to coil some cable differently or that you actually fixed it. Without seeing the root cause you can't know that the problem will not come back. 'Sopes are useful and Gen is right, The Chinese digital ones are good and worth themoney. The older vintage analog scopes are good too if you do not want to pay so much. Having one vs. not having one matters a thousand times more that what kind you have.
Just do make sure the bandwidth is at a bare minimum 50 MHz, but 100 is better. That said a logic analyzer is almost as good as a scope and costs about $10. These things can only work on logic-level signals. They allow you to plot up to 8 or more signals. You can look at any signal AFTER it has been shifted to a logical level. THese do nothelp yu see noise, they only record high/low or 1/0 levels but still very usfull. There are MANY Saleaeclones on eBay. On Mon, Oct 11, 2021 at 6:54 PM Gene Heskett <ghesk...@shentel.net> wrote: > On Monday 11 October 2021 17:32:31 Peter Hodgson wrote: > > > Thanks all for your continued support. > > > > I’ve now separated all the earth grounding to individual cables going > > to one bolt in the steel control enclosure which is then 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. > > That smells like a ground loop. If disconnected at the star bolt, it > should be an open circuit, to ground or anything else. > > > 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. > > They do. > > I generally run my motor cables in shielded cabling. The stepper drivers > control the motor current by turning themselves on and off at an > ultrasonic frequeny we don't hear. If you can find "starquad" cabing in > a gage heavy enough it doesn't run warm at the motors current. It is > actualy the gold standard microphone cable, a top quality microphone > cable available in several gages, all VERY flexible, get the lowest gage > number Suzan has. 22 gage IIRC. Ground the shielding drain wire at the > star bolt, trim and insulate it at the motor end. > > > > 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! > > Digital storage will show you stuff that cannot be seen on an analogue > scope. Definitely worth the extra sheckles. Some of this stuff is at 100 > or more megahertz. And tends to be very dim on a analog scope. I > actually have 3, a 30 yo Hitachi 100 mhz dual trace analog, much better > than a tek of the same vintage, a 5 yo digital with the same specs you > can get for $300 or so today, and I just bought Siglents best, a 4 > trace, 350 mhz digital sampler. It also costs a down payment on a new > small car. Inheritances are handy. > > > I’ll keep you posted. > > Please. > > > 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 > > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
