Old case line. SLC 5/04 with a 1747-SDN scanner on DeviceNet, thick trunk. Somebody extended the trunk out to the new stacker back in 2015, so it's a long one now.
The nodes at the stacker end, three 1791D CompactBlock I/O and a PowerFlex 40 with the DeviceNet card, keep dropping out. Scanner display cycles 78 and 72 for nodes 22, 24 and 25, then back to 80 when they come back. The near nodes never drop at all.
I swapped node 24 for a spare and got exactly the same, and both terminators are there, 121 ohm, checked with the power off. Is the far end starved for power, or is one of those nodes dragging the rest down with it? Would dropping the baud be worth a go before I start pulling a long trunk apart?
Seen this on our palletizer trunk after it got extended. How long is it exactly, and what baud?
Paced it out again this morning, roughly 290 m of trunk end to end, and the drops are all short. 250 kbps, been that way since the scanner went in. 23.6 V at the far end, so I'm not sure it's power.
23.6 V rules power out. The trunk's too long for the baud rate, that's all. Thick trunk limits are 500 m at 125 kbps, 250 m at 250 kbps and 100 m at 500 kbps, and you're at 290 on a 250 limit, so the far nodes see reflections and corrupt frames and the near ones don't.
Two ways out of it. Drop the whole network to 125 kbps: every node's DIP switches or parameter, then the scanner in RSNetWorx for DeviceNet, then power cycle the lot, because one node left at the wrong rate takes the bus down with it. Or shorten the trunk under 250 m and hang the stacker nodes off a drop. The first one costs nothing.
Set every node to 125, switches on the 1791Ds, the parameter on the PowerFlex 40 card, scanner rate in RSNetWorx. Power cycled everything. Now the scanner sits at 91 and nothing talks at all, which I guess is progress of a sort.
Pretty sure one node you missed is still at 250. One wrong rate and the whole bus goes off, that's your 91. Check the one you didn't touch, usually the spare you dropped in last week.
Carl was right. The spare at node 24 was still on 250, its DIP switches were under a label and I never lifted it. Set it, cycled it, and the whole network came up at 125, scanner sitting at 00, no drops since Monday.
So it was the 2015 extension all along, 290 m of trunk on a 250 m limit at 250 kbps, and 125 kbps on every node and on the 1747-SDN fixed it. Nobody changed the rate when they added the stacker and it ran nine years on the edge.
Still amazed it ran at all. Thanks dieter_k, carlh.
Nine years past the limit and it ran. I wouldn't have believed it.