Communication Offline error message using controllogix


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I am having a problem of "COMMUNICATION OFFLINE." We are using controllogix redundancy system and two 1756 ENBT card. The Ethernet cable from two ENBT card is directly hook up to CISCO HUB 32port. There around 12 outgoing Ethernet cables, 6 of them are for wireless Ethernet Communication using "RadioLinx." One of them is a fiber optic used for our SCADA communication, and the rest is used for HMI PanelView Plus communication. For four years it is working fine just recently when we frequently got "COMMUNICATION OFFLINE" Fault. There is no switchover from PLC 1 and PLC2 in the time of communication failure, we did replace the CISCO HUB but still problem not solve.

I really don't know what is causing the offline, I’m guessing that it might be one of those outgoing Ethernet cables.

Please help and thanks in advance.

Just a thought... I have found that RJ45 connectors in use for multiple years sometimes exhibit some unusual errors, often associated with vibration of the equipment. It wouldn't cost anything and only a few minutes of your time to extract and re-insert the connectors at both ends of the cable.

It probably isn't the cause but I had something similar happen with a servo motor. Had occasional encoder faults shutting down the axis with no apparent cause. It was tracked down to a dirt/oxidation on the encoder connector. Removed the connector and re-installed the same device and the problem went away. Note that this was on a mil-spec type connector, not something a light as an EtherNet connector.

Any time you are dealing with low current signals there is always a risk of bad connections. I sometimes think that there is less MTBF in the equipment I am installing than in the connections I am making to it.

Can you explain exactly what device or software package is displaying the "Communication Offline" error? Is it RSLogix 5000, or RSView, or Wonderware, or something else?
Hi All,

Thank you for the reply.

The Redundancy System PLC 1 and PLC 2 is our Anode Management System (AMS) PLC, the brain and the master, using a fiber optic cable for the SCADA, the rest of the equipment is slave. The communication offline fault is displayed on SCADA monitor. We generate the communication offline fault bit through the define communication watchdog for individual connected equipment communicating with AMS. We set it for 10 seconds (Receive and Transmit) if no update then fault will be generated. Whenever failure occurs I check the watchdog or heart bit and it really stops updating, and sometimes communication automatically restores and sometimes I need to power down the HUB and power up again because it freezes or something.

A week ago I isolated the SCADA Ethernet connectivity, by putting a new CISCO HUB for the used of SCADA alone, the second CISCO HUB I used it for the rest of the equipment Ethernet connectivity loop from the first HUB. The failure of communication happens to all, except the SCADA. Once happen each equipment will display Offline Fault on the SCADA.

All the equipment is using RSLogix5000 and our SCADA is also RSView. Six of the equipment is using RADIO LINX wireless Ethernet communication. They are all individually communicating to our AMS.