RIO Drop having communication issues

[speakerman]

Hello everyone; Long time no chat, been way too busy. Got to cruise the forums for some pay-back after this, it's been a while since I gave back. We've run into a problem beyond my experience, so I have a question for people well versed in the Modicon PLC remote I/O world. We're having some drop-outs with a remote rack of a quantum PLC system, and can find no problems with the cables, taps, or the RIO drop card. We're seeing what seems like a lot of retries, but then we don't know what constitutes a lot. There are 10 drops on this PLC. Drops 1, 9, and 10 are quantum and drops 2-8 are old 800 series. It's a CRP931-00 remote I/O head with a bunch of J890-001 cards, and two CRA-931-00 for the new racks. Funny, but the two quantum racks have the most retries of all the cards. A couple of the 800 series have almost no retries by comparison. The quantum drop 9 has had dropouts at random, sometimes twice or three times a day, sometimes none for a couple days. Causes major problems, obviously. Drop 9 is actually at the end of the trunk cable, so it's got the terminal resistor on one tap. Drop 10 was added later between drops 3 and 4, and has more retries than either of them, but no dropouts. We've asked Schneider for a contractor who can perform a RIO cable network integrity test, but it seems to mostly be these two quantum heads with the most retries, and only the one has been dropping out. Is there anyone who has seen something like this and can comment? We've changed almost everything around it and there's been no change to the retries, and the occasional drop-out still happens. Hope things are going great for everyone out there. Happy programming, speakerman.

[Modiconbob]

What type of trunk cable (RG-6-RG-11-quad shield?) are you utilizing? How many drops are on the sytem? Do you have a rough idea of the total length of the cable? What test equipment have you used to trouble shoot? Bob www.deltaautomation.com bobculley@deltaautomation.com

[speakerman]

Hey Modiconbob; Thanks for the reply. It's RG-11 trunk, quad shield, but we have since discovered the route has been done improperly to the one drop we're having issues with. The original cable is in conduit on the side of the cable trays, passing above drop 9 on the way to drop 7. There used to be the terminal resistor in drop 7, but when 9 was added they just pulled a tech cable of RG-11 back to 9, laying it in the cable tray with everything from 240VAC to 600 three-phase. It has been this way for a long time without the issue cropping up as far as we know, but over time more and more stuff has been added to that cable tray, so the chance for noise has been slowly increasing over the years. The whole network is about 1200', but most drops are within the first 500. There's a 650' run from drop 5 to drop 7, (They are not in numerical order. It's 1, 8, 2, 3, 10, 4, 6, 5, 7, and 9 in that order. From 8 to 5 is about 400' total. The document with that information has been taken away right now; it's not handy so I can't be exact. We have a plan to add more conduit down to the PLC cabinet, then pull the original trunk cable back to drop 9 and pull a new RG-11 in the remaining conduit to drop 7, making it the end of the line again. This will eliminate the tech cable in the cable tray, and all the coax will be in proper conduit isolated from the rest of the wires. Putting drop 9 in line to drop 7 instead of daisy-chaining back will reduce the length by about 100' overall. Drop 9 has about 4 to 6 retries per second on average. The other drops have between 1 and 2, sometimes none. Very occasionally we'll see three retries in a second on the other drops. The drops closest to the head are the best, obviously, and have the fewest of all. The duration of the dropouts on drop 9 are so far only for one scan of the PLC, and maybe once a day on average, so it is very marginal at this point. We do not have testing equipment for the cable system onsite, and were looking for a contractor from Schneider who could come and assess it. Now that we've discovered this routing issue, we'll address it for sure and see how many retries we have after that is done. Thanks for anything you have to add. This may be a "we post our resolution" kind of path, and that's fine with me. Originally we didn't think we had a cable problem, but now it looks like we do. Will let you know what happens when the cable is re-done. Happy programming, speakerman.