Intermittent Communication Issues

[rcorbett11]

I Have 2 Compact Logix L35E's communicating over ethernet. The only reason the two communicate are for Truck and Railcar Loading Messaging for pumps. But on the one controller I have 4 Cooling tower Fans that are on the PLC, and every time the communication goes it knocks all the cooling fans down. I've basically thrown everything I can think of at. I've Changed the controller, I've changed the power Supply, Checked the Patch Cable for the PLC to the Network Switch. Had our IT department check all the network switch ports for anything unusual and there is nothing. I'm monitoring the communication with a Get System Value so I know that its a communication issue causing it. Anybody have any oddballs to throw at it?

 

[dmroeder]

Enter your controllers IP address into a web browser, the build in web page as some good statistics about all the connections being made to the PLC. If you can screenshot some of the pages, that might help give a clue as to what is going on.

Welcome to the forum.

 

[VAN]

I Have 2 Compact Logix L35E's communicating over ethernet. The only reason the two communicate are for Truck and Railcar Loading Messaging for pumps. But on the one controller I have 4 Cooling tower Fans that are on the PLC, and every time the communication goes it knocks all the cooling fans down. I've basically thrown everything I can think of at. I've Changed the controller, I've changed the power Supply, Checked the Patch Cable for the PLC to the Network Switch. Had our IT department check all the network switch ports for anything unusual and there is nothing. I'm monitoring the communication with a Get System Value so I know that its a communication issue causing it. Anybody have any oddballs to throw at it?

RSLogix 5000 Task Monitor Tool - this might help a little too see how everything is running, the web page would probably give similar results.

Out of curiosity, does the PLC fault?

If I were you, I'd rebuild the logic to not care if the communication dies and have the PLC be standalone. So if communication is working, great, if it dies it can maintain the cooling towers or whatever else it needs to run.

 

[atc222]

Take a look at the system time slice allocated for communications.

I've had similar issues in the past, resolved by increasing from default of 20% to 40%.

 

[Firejo]

Depending on how frequently it happens you could setup a wireshark session and try to capture the communications failure. That will give you exactly what is happening at all of the different Ethernet layers before, during and after the failure.

 

[Ken Roach]

Welcome to the PLCTalk forum community !

Let's review the basic connectivity we know about:

CompactLogix L35E Controller A
  - Fan VFD1
  - Fan VFD2
  - Fan VFD3
  - Fan VFD4
  - CompactLogix Controller B Produced/Consumed Connection

CompactLogix L35E Controller B
  - CompactLogix Controller A Produced/Consumed Connection

Are there other I/O connections on either system, and do any of them fail as well ?

I think you're saying that sometimes you lose connectivity from CompactLogix A to all of its IO connections, including all four fan VFDs and CompactLogix B.

How often does this connection fail ?

Can this be recreated by disconnecting the network path between CompactLogix B and CompactLogix A ?

Which controller did you put the GSV instruction in, and which connections was it looking at ?

How do the connections re-establish and the system come back to nominal ? Does it happen by itself, or do you have to cycle power or disconnect/reconnect anything ?

 

[Rayman_7676]

You may want to verify that the comms setting for your ethernet ports are configured correctly. I would usually use Auto Negotiate on both PLCs.