On Sunday 26 March 2017 03:01:17 linden wrote: > Hello All > > Should I ground both ends of the shield for shielded pair?
No, only one end. Actually I think best practice is a single #10 bolt in the middle of it all, to which all grounds and all cable shields are connected, with the grounds going here and there both heavy and insulated so they won't setup a ground loop by touching something on the way to connect a ground on something else. This is called a star ground. Shielded cables such as those from a stepper driver to its motor, I cut into the plastic sheath and separate the drain wire, and solder a 2" piece of 1/4" flat braid, with an eyelet crimped on one end, the other end folded over the drain wire and soldered to it, using a 2 or 3% silver bearing solder. Good connection, and stronger than the eutectic alloys. The eyelet gets dropped over the bolt and the nut replaced and tightened. > I am not > sure what the best practice is see pdf attached for what I have now in > black and the chunk in red I am not sure about. I would not depend on the connector shell, trimming the shielding short so it doesn't touch there, nor at the motor, but does have the short tab described above soldered to the drain wire as it goes past the bolt on its way out of the box, and connected to the common ground bolt. You should run a piece of the braid from this bolt to the ground symbol terminal on the power supplies, then feed the drivers power from the psu's via twisted pair, and it may help if a ferrite clamp-on is applied close to the drivers motor outputs, and another applied at the psu outputs, so the bead covers both wires in each case. This will block the "longitudinal" noise but has no effect on the psu's switching noise. In my case the vfd's motor wires are in the same 1" conduit as the power coming in is in, and I had to put a 3 phase corcom 20 amp "brick wall" in the circuit as close to the vfd's output terminals as was practical, getting rid of the vfd's noise it was injecting into the incoming power for all my electronics. This has not appeared to have affected the vfd. One other thing, there is not any filtering or shielding in the 5v runs to the encoders I installed to replace the hand cranks removed from this Sheldon 11x36 lathe, its all in cat 5 cable, and the returns from the encoder were loaded with high voltage electrical spikes on the corners of what should have been the 4.9 volt or so square waves it produces. So those signal wires now go past a board with 6 each (I buy them in 100 packs) 1n914 diodes to ground for each signal wire so as to clamp the positive peaks to about 4 volts, and while its working, I may add another diode faceing the other way to clamp any ground undershoots to about -0.55 volts to protect the 7i90's inputs. This board in particular seems to be more easily damaged by the noise spikes and static electricity*, than a 5i25, which I also am familiar with, but the 7i90 gives you I/O to throw away, ( 72 minus the generators and encoders enabled ) whereas the input facilities of the 5i25 are limited to the 5 the parport offers, per connector, which it has 2 of. *static electricity, generated by my butt rubbing on the garage door behind the lathe as its been covered by an additional layer of 2" blue styrofoam from Lowes, adding another R11 to most of the door making my otherwise well insulated garage very easy to heat or air condition. So I have to slip on one of those wrist grounding straps when I'm working on the electronics to keep my charges down else I can blow the 7i90 with my generated static. I've BTDT too. :( > The only other connections I have are: > - 24 volt supply for the mesa board going into TB3 pin22 as > +24vdc - the corresponding ground from the power supply going into TB3 > pin 23 This - supply wire to T3-23 s/b grounded as it goes by that bolt. > - a jumper going from IO ground pin 9 on JP4 of the servo drive > to TB3 pin 24 As should this wire UNLESS its internally connected to the TB3-23, verify with an ohm-meter. Proper grounding can be tricky because you don't always know whats in the box. So keep a meter handy. > Thanks for any help and advice > linden Thats my $0.02, but adjust for inflation since 1934. :) I am also a C.E.T. 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
