DeviceNet Issue

[Gordo26 0]

Hi all, I have a CJ1M CPU-11 PLC with an attached CJ1M-DRM21 DeviceNet unit attached. This unit is being used as a slave and has the master function disabled, this unit is Node #6. This unit is mounted in a panel used for a scanning station, there is an exact replica of this station located about 50ft and it is set as Node #7. Node #7 is on one end of the network (ie: the EOL resistor is located near this nodes branch). Currently I am getting a large number of Remote IO Communications Error logged in the master DeviceNet unit for the network and the errors are logged to Node #6. There are no errors showing on the 7-segment displays on any of the units at any time that I have been watching. Also, I removed the branch cable leading to Node #6 at one point and replaced it with a new cable, the problem seemed to have stopped for a short period of time but then it reappeared again (maybe 10min or so). I discovered the problem after seeing one of the DeviceNet inputs on Node #6 flickering on and off, which I assume is a direct cause of the Remote IO Communications Error. Has anyone ever seen this type of problem, is there anything that you could think that I could try to fix the problem? *Note: The voltage between CAN-H and V- is 3.2V, the voltage between CAN-L and V- is 2.4V and the voltage between V- and drain is 0.1V (Node #6 and #7). The network voltage at both Node #6 and Node #7 is 23.8V. Edited 6 Jan 2012 by Gordo26

[PdL 71]

If you say you were seeing the Devicenet inputs "flickering", are you referring to an input LED or watching an input digital status in the PLC? If the first, no matter if there are communications, the input LED is just a circuit when power applied the LED lights up. If it flickers, you might want to look for the source of your problem in the power supply. Do you have separate power supplies for I/O and Devicenet power?

[Gordo26 0]

Thanks for the response, what I'm seeing is bit 4000.00 flickering on and off. This is a DeviceNet input coming from another PLC. I do have separate power supplies for DeviceNet and my I/O. I'm logging a ton of Remote IO Communications Error on the master PLC for the network and the error code identifies the problem as coming from node #6, which is where I see the flickering bit. I've changed out the cable coming from the T branch and the problem still persists. Note that I have a exact replica of this slave PLC (node #6) at one end of the trunk set as node #7 and it has the same bit (4000.00) coming from the master and isn't flickering. Would I be right to say the problem is with node #6 or could the problem be elsewhere?

[Gordo26 0]

In going through the network and drawing out the topology and where the devices are located I think I found the solution. An outside company was contracted to put the deviceNet network in for us and I've found we are missing an EOL resistor which could be the cause of the problem.