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SLC 5\05 Ethernet Problems Locking Up

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Hi Guys I could use some help please with an SLC 5\05 problem that we are having. One of the sites that we maintain has 12 SLC 5\05 processors which are all connected via a fibre optic network over a distance of approximately 5 kilometers. The network was installed 9 years ago and has been functioning trouble free until a couple of months ago. The fibre converters are Hirschmann RS2-3TX\2FX and the fibre is multimode 62.5\125. There is no redundancy and the network is daisy chained straight through from the first to the last processor. Also on the network are 10 PC's running Wonderware Intouch SCADA, these communicate through two I\O ABTCP I\O servers. There are also 8 off PanelView Plus HMI terminals at various points throughout the network. We have recently had a strange occurrence where a number of PLC Ethernet channels appear to freeze up at exactly the same point in time. The green Ethernet LED goes solid and the processor loses all Ethernet communications to the SCADA PC's and to our maintenance laptop running RSLinx. The fault can occur on one or a number of PLC's at exactly the same point in time and each processor has to have its power cycled in order to recover from the fault and to re-establish comms. The control supply to the processors is derived from a number of separate High Voltage transformers and in some cases totally seperate electric board supplies as they are located at another site. This would appear to rule out a mains power quality problem. There appears to be no pattern to the problem. Any advice would be greatly appreciated. regards Steve

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When the fault only occurs on 1 PLC, is it always the same PLC? Is there anything setup for datalogging, so you can get more info on system conditions when this issue happens? RSLinx has an Event Log, on my copy of RSLinx Classic Gateway 3.60 you have to go to "View" then "Event Log". I have personally never used this log before but it maybe helpful.

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Use Wireshark on one of the computers. Don't leave wireshark running non stop or you'll run out of memory. Then use dumpcap to store the logs to file (instructions here - scroll down to the Solution, there's a link to a UI tool at the very bottom) You can then use Wireshark to analyse the file captures you've made. When you have a problem, go back to that point in time on your log files and see if there was a network storm or something on your network, and what IP address it came from. This should help you determine the source of the problem, if not the cause. Edited by MrAutomation

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MrAutomation raises a great suggestion. Wireshark reports can point you to the culprit, but you will be weeding through a lot of data. You could program some event registers in your PLCs. Determine a handshaking tag that you can buffer the CPU date/time to when the handshaking tag goes low. Since you have a daisy-chained network, you could program to pass and increment a tag around your network to be monitored at a last location. Also, since your network is very, very large, keep a close eye on grounding practices. Over time from when the system was first commissioned, I have been bit in the butt before with a new noisy process that goes in and flushes out poor grounding practices in a working system.

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Thanks for your help guys I am installing a monitoring laptop this week that will be running Wireshark to try and capture some data that could help. I will also check the event logs on RSLinx and get the local electricians to check all of the ground practices. Thanks for your help, I will report back.

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