Still trying to digest this in between working... On 1/10/2016 7:48 AM, Bertho Stultiens wrote: > On 01/10/2016 12:44 PM, John Thornton wrote: >> Well none of the suggestions about star grounding did any good. In >> fact they made the problem worse than before, so bad I could not even >> get 2.6 to run. > That may suggest a couple of things being wrong simultaneously: > 1) you may still have loops in the 0VDC which are crossing power > domains. These /are/ hard to detect with many devices connected together; > 2) there are impedance mismatches in the signal wiring (this one often > works together with 1); > 3) shields may pick up noise they should reject. > > The question is how to reduce the practical problems, not how to > eliminate all theoretical problems. That is the hard part. > > >> Off this list I was sent the AB servo best wiring practices pdf >> which explained how to reduce noise in a servo drive enclosure. I >> followed the advise as much as possible and after removing all my ground >> wire antennas I was back running with an occasional sserial error. The >> short explanation is to terminate the shields to a ground plane as close >> as possible to the point where you take the shield/drain wire from the >> cable. I still have a cable bundle running to my switch box that is >> parallel wires and I might replace that with some twisted pairs. Photos >> at 11. > You refer to this document? > http://literature.rockwellautomation.com/idc/groups/literature/documents/at/motion-at004_-en-p.pdf > > That doc explains very well how to separate into different power zones. > Also, it makes a good case of shielding and how to do it properly. BTW, > note that it uses protective ground as shield potential and _not_ 0VDC. > That is also why the argument of two-sided termination of the shield is > appropriate (see page 21). > > But all this does not save you from impedance problems. The sserial > errors are interesting because it is probably something you actually can > measure with an oscilloscope. > > You should be able to see the signal integrity and whether you have > reflections of the signal at either end of the cable. > > The sserial connection has a great potential for a loop. See attached > image for illustration. The image has a shielded connection between two > devices, which is good. However, the 0VDC connection (aka GND), which is > embedded in the shielded connection is shorted outside the cable via a > protective ground connection through the PSUs. This means that part of > the signal return may circumvent the constraints of the signal cable and > that creates an unbalanced path. Effectively, it means that the shield > is now part of the cable's impedance, and that is guaranteed to be off > by a factor. > > You can check for this scenario by disconnecting the sserial connector > at one side and measure 0VDC vs protective ground on the connector on > the other side (and the other way around). You are in trouble when > measurements on both sides indicate a connection between 0VDC and > protective ground. > > If you only have one PSU for both devices, then you are potentially also > in trouble. The PSU will then act as the loop facilitator (through two > distinct 0VDC connections). However, the effects are more subtle and > depend on coupling effects. > > The rule for a shielded cable is that all energy must be contained > within the cable to be effective. In other words, the sum of all > currents in the cable's wires must be zero. Bypassing some of it may > cause impedance and therefore signal integrity problems. > > > > ------------------------------------------------------------------------------ > Site24x7 APM Insight: Get Deep Visibility into Application Performance > APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month > Monitor end-to-end web transactions and take corrective actions now > Troubleshoot faster and improve end-user experience. Signup Now! > http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users
------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
