Wire flexability for data collector

rpoet

Member
Join Date
Jun 2008
Location
New York, NY
Posts
536
All,

I have a bit of a strange issue that I am trying to solve; we have an application where several trolleys traverse a track, and receive their power and control data through rails by Wampfler. We are using the 811 series for power, and the 815 series for data. Three phase power is no problem, but we are running into issues with the data rail and its collectors. We are sending Profibus over the rails, and amazingly, I think, we have excellent data reliability.

Our problem is the physical connection of the Profibus cable to the collector / skate. It is spring loaded and moves as the trolley moves, so as to follow and maintain contact with the rail. This constant movement is causing the individual cores in the Profibus cable to fatigue and break.

Since a picture's worth a 1000 words, here's a picture to make things a little clearer:

data_rail.jpg


Wampfler has suggested the use of high-flex single core unshielded wire from each collector skate to a junction box, where it would be connected to proper Profibus cable, but the idea has been only lukewarm-ly accepted by our systems integrator. They say that the individual wires don’t have the same characteristic impedance as Profibus cable, and therefore will interfere with data transmission. I can’t argue with that, but I counter that the parallel data rails that are almost 350 feet long don’t come anywhere close to the characteristics of Profibus cable either, and there seem to be no problems with that.

This particular run of Profibus is book ended by power rail boosters, so presumably, the signal levels are much higher than “proper” Profibus (+/- 24v, I think). This is apparently what helps the run work over the data rails, according to our integrator. Will an extra few feet of single core wire really make a difference in this case? As you can tell, I’m a bit of a novice with Profibus, and am looking for independent ideas to solve this issue.

Another possibility might be some super flexible Profibus cable, but I really haven’t found much. The closest I’ve found is Belden 3079E, but it is 22awg, 7x30 construction; really not too much finer (if at all) then what we have now.

I think the problem stems not so much from the flexibility of the cable as a whole, but more the fact that the stress of bending is concentrating right at the termination of each core. The high flex wire is supposed to help that, according to Wampfler. The other thing that may help, regardless of the wire / cable we choose, is to add a drop of glue between the wire’s insulation and the end of the ferrule. This will take the stress off the wire strands, and transfer it to the insulation. Might something like Duco cement be a good choice?



Thanks for any ideas.



rpoet
 
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Lapp or Helukabel , 2 manufacturers of highly flex cables for drives and comms and anything in between may be able to help.
If the problem is indeed the cable itself!
EDIT: Steiner Electric can get you Helukabel (though I remember a rep out in Elgin) , Lapp reps are in Wheeling I think (just realized you are in Chicago)
 
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