I think you are right and will just try to dig a little bit deeper. A shield is primarily intended to prevent electrostatic coupling from the outside world. So by grounding in the consuming end the shield will get the ground potential of the consumer and the signal cables will be shielded from different external electric fields. This should motivate why as you say the shield should be connected in this end only. If there are current there is also a potential difference.
I consider the VFD to be a noise source since it have common mode voltage which will emit an electrical field. There is also a capacitance between the VFD cables and shield. Since Shield impedance on high frequency is far from zero the shield around the VFD cables will not be at GND potential. The most common method is to increase common mode inductance by a filter but I have also seen active filters which reduce the common mode voltage and multiple step voltage inverters. Nicklas Karlsson On Mon, 16 Mar 2015 09:41:15 -0500 "Steve Stallings" <[email protected]> wrote: > I would recommend that shielded signal cables have the > shield grounded only at the end where the signals are > consumed. > > If a ground is needed by the device at the end of the > cable, you should use a conductor inside rather than > the shield itself. > > If there are signals going both ways, provide the shield > ground connection at the end where the most sensitive > signals are consumed. > > The purpose of grounding only one end of the shield is > to prevent current from flowing in the shield itself and > distorting the signals due to electromagnetic coupling. > > A shield is primarily intended to prevent electrostatic > coupling from the outside world. > > If the cable does not contain sensitive signals, such as > the power cable from a VFD to the spindle, then it is > acceptable to ground both ends of the shield. > > Steve Stallings > www.PMDX.com > > > > -----Original Message----- > > From: Matt Tucci [mailto:[email protected]] > > Sent: Monday, March 16, 2015 7:54 AM > > To: Enhanced Machine Controller (EMC) > > Subject: Re: [Emc-users] VFD causing limits to trip. Huh? > > > > Are the shielded wires only grounded at one end and at the > > controller end? > > > > On Sun, Mar 15, 2015 at 1:22 PM, Karlsson & Wang < > > [email protected]> wrote: > > > > > I think grounding is the most important. There are normally > > a common mode > > > voltage at the inverter output to motor so the inverter > > power ground will > > > bounce around each time inverter is switched. If this > > bouncing is coupled > > > to the logic ground there may be a lot of problems. > > > > > > Nicklas Karlsson > > > > > > > > > > > > > > > On Sun, 15 Mar 2015 14:39:24 +0000 (GMT) > > > [email protected] (Russell Brown) wrote: > > > > > > > > > > > I promised to report back so... > > > > > > > > I fitted the filter (Schaffner FN2030 Series 16A 250 V ac > > 400Hz) on the > > > > VFD mains input and that did make a difference. My > > failing case job ran > > > > 70% of the way through where without it the job failed > > 10% in. Not the > > > > complete solution though. > > > > > > > > I then tried a ferrite core (mains clipon stylee) on the > > input of the > > > > field power supply. No difference. A ferrite core (ring > > with both > > > > wires looped through it a couple of times) on the output > > of the 12V > > > > field power made no difference either. > > > > > > > > A ferrite core (ring as above) on the limit switch wires > > fitted at the > > > > Mesa end made no difference either. > > > > > > > > So... finally I replaced the limit switch wires with > > shielded cable > > > > (grounded only at the Mesa end). That seemed to do the > > final trick and > > > > the job ran all the way through. > > > > > > > > Of course I don't know if this is a 100% fix or just enough to get > > > > through my failing case (other jobs without all the above have run > > > > fine). I guess time will tell. > > > > > > > > Hope that's useful for someone. > > > > > > > > -- > > > > Regards, > > > > Russell > > > > > > -------------------------------------------------------------------- > > > > | Russell Brown | MAIL: [email protected] PHONE: > > 01780 471800 | > > > > | Lady Lodge Systems | WWW Work: http://www.lls.com > > | > > > > | Peterborough, England | WWW Play: > > http://www.ruffle.me.uk | > > > > > > -------------------------------------------------------------------- > > > > > > > > > > > > > -------------------------------------------------------------- > > ---------------- > > > > Dive into the World of Parallel Programming The Go > > Parallel Website, > > > sponsored > > > > by Intel and developed in partnership with Slashdot > > Media, is your hub > > > for all > > > > things parallel software development, from weekly thought > > leadership > > > blogs to > > > > news, videos, case studies, tutorials and more. Take a > > look and join the > > > > conversation now. http://goparallel.sourceforge.net/ > > > > _______________________________________________ > > > > Emc-users mailing list > > > > [email protected] > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > > > -------------------------------------------------------------- > > ---------------- > > > Dive into the World of Parallel Programming The Go Parallel Website, > > > sponsored > > > by Intel and developed in partnership with Slashdot Media, > > is your hub for > > > all > > > things parallel software development, from weekly thought > > leadership blogs > > > to > > > news, videos, case studies, tutorials and more. Take a look > > and join the > > > conversation now. http://goparallel.sourceforge.net/ > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > -------------------------------------------------------------- > > ---------------- > > Dive into the World of Parallel Programming The Go Parallel > > Website, sponsored > > by Intel and developed in partnership with Slashdot Media, is > > your hub for all > > things parallel software development, from weekly thought > > leadership blogs to > > news, videos, case studies, tutorials and more. Take a look > > and join the > > conversation now. http://goparallel.sourceforge.net/ > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming The Go Parallel Website, sponsored > by Intel and developed in partnership with Slashdot Media, is your hub for all > things parallel software development, from weekly thought leadership blogs to > news, videos, case studies, tutorials and more. Take a look and join the > conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
