We just started up the 35 servomotor machine which inspired this thread, and unfortunately we began to have some problems with some proportional valves (4-20ma) cabled alongside the servomotors. Of course, some people (including the field service guy from the machine manufacturer) pointed towards the excess cable coiled below the control room´s floor as a possible culprit, since each of the machine´s 120+ cables has about 10 to 20 meters excess length.
Fortunately, the problem turned out to be a software configuration issue and has pretty much been taken care of by now. I had trimmed the 35 power cables during installation, but not the resolver and other assorted control cables. Disregarding my protests, they made me trim 10 multiconductor cables carrying 4-20 ma signals to eliminate coiling, before the real problem was corrected.
In order to better defend myself from other similar situations, I still have a question regarding the previous postings: if there is no net magnetic field sorrounding a servomotor cable, and therefore no inductor effect if coiled, why is it still recommended to keep them separate from resolver or control cables? If there is indeed some small residual noise/interference from the cables, wouldn´t coiling them make it worse, not from the coiling itself but from having more cable bundled within a smaller volume? And finally, please pardon my ignorance again, could coiling of low level signal cables (like resolver cables) make them more susceptible to picking up noise? Again, I´m just asking myself questions that somebody could shoot at me and which I can´t technically respond. I still have a bunch of resolver, 4-20 ma signal, and other assorted digital I/O cable all coiled together in the control room, but trimming them up would be pretty challenging and difficult, because they are multiconductors (30+ wires on some of them) with special connectors on both ends.
p.s. I almost forgot another issue: I have an ethernet cable running in in its own 1" conduit, and for about 20 meters this conduit runs parallel to a tray carrying 5 servomotor cables, about 1/2 meter from the closest of them. Communication is really bad, almost null, so we had to run another ethernet cable to get things going. The cable is physically OK. Could the closeness to the motor cables be causing problems, or is 1/2 meter far enough? These are small motors, less than 1kW, from the same machine mentioned above.
Thanks a lot again in advance for your comments to this novel... I mean post.
