On Wednesday 13 October 2021 06:06:06 Peter Hodgson wrote: > I just tested the VFD shield and supply line shield and both are open > circuit when not connected to the start bolt. > > There are three AC motors: Spindle, Oil Lubrication and Coolant Pump > that are all grounded to the machine frame via their mountings but I > have also ran individual earth cables to the star bolt. Is that good > practice?? > > Pete
I wouldn't think so Pete. Only the house static ground, the third pin of the power plug, the bare wire in romex cable, s/b connected there. Your connection to an earth ground is paralleling the static ground to earth, normally made in the meter head box or just below it. Thats the one and only place where its even legal to connect static ground and neutral together here in the US. That earth connection is potentially a huge ground loop. The machines themselves are, I assume sitting on concrete, a relatively poor conductor, and their frames should also be connected to that bolt unless the bolt itself is on the machine frame which will accomplish, barring paint, the same thing. > On 12/10/2021 02:50, Gene Heskett 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 <[email protected]> > >>> 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 > >>> [email protected] > >>> https://lists.sourceforge.net/lists/listinfo/emc-users > >> > >> _______________________________________________ > >> Emc-users mailing list > >> [email protected] > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > > Cheers, Gene Heskett. > > _______________________________________________ > Emc-users mailing list > [email protected] > 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
