Thank you John, that looks like a really useful document. Pete
> On 13 Oct 2021, at 16:49, John Figie <[email protected]> wrote: > > > > John Figie > > >> On Wed, Oct 13, 2021 at 10:15 AM Peter Hodgson <[email protected]> >> wrote: >> >> On 13/10/2021 15:43, Gene Heskett wrote: >> > 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. >> >> I think I might be creating confusion here with my terminology. When I >> say 'grounded' I mean the motor chassis has continuity to the machine >> frame via it's mounting bolts so therefore is 'earthed' BUT I have also >> run an individual earth cable from the motor chassis to the star bolt. >> No AC Neutral or dc 0v are taken to the machine frame or earth (as far >> as I know). My question is ......Is it good or bad practice to have the >> motor chassis with mechanical continuity to the machine frame AND >> continuity to the star bolt with an earth cable i.e. two routes to earth?? > > Yes I think this is good. In fact for industrial servo drives there is a > green earth conductor in the motor power cable that > provides a ground from the motor frame to earth ground. This is needed for > electrical safety as there is no requirement for > the motor frame to be bolted to a metal frame that is also earth ground - but > that is a good practice. > > I am a professional electrical / electronics engineer (44 years experience) > and I designed electronics for PWM servo drives for industrial applications. > I have also designed offline switch mode power supplies for industrial > applications. The products that I design and work with have to not only > function but must also meet EMC standards for Radiated and conducted > emissions, Immunity to EFT (Electrical Fast Transients), Surge transients, > Immunity to radiated and conducted RF, and ESD (Electrostatic Discharge) all > to the industrial levels defined by the international standards. The surge > transient immunity standards in particular are meant to provide immunity from > surges in power and ground caused by lightning. > > I think the best advice I can give you is some reference material that will > help you wire your machine using best industry practices. I have attached an > application note by SEW, a German company and a link to best practices for > installing servo drives in industrial applications by a well known US company > Rockwell Automation. Please pay particular attention to shield terminations > as this "key". It is best to have a metal plane where your equipment is > mounted. This metal plane should be connected to earth in one place with a > wire or braid for low impedance. You should keep shield "pigtails" short or > zero length as illustrated in the application notes. > > Rockwell Automation uses Ethernet to connect and control industrial I/O and > drives using real time coordinated motion to a controller so, to make this > all work reliably in an industrial environment requires correct wiring and > grounding. > > http://literature.rockwellautomation.com/idc/groups/literature/documents/at/motion-at004_-en-p.pdf >> >> I didn't build this machine control. It was an eBay purchase where the >> LCNC computer was lost and seems like it had been passed around a bit >> whilst various people tried to get it running again. It's running quite >> well now after I bought it and got my head around LCNC but I'm now >> trying to iron out these last few wrinkles!! >> >> Pete >> >> >> >> >> >> >> 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. >> >> _______________________________________________ >> Emc-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/emc-users > > <SEW EMC in Drive Engineering - Theorectic Fundamentals (11535814).pdf> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
