geetee1969

DeviceNet

7 posts in this topic

I have enjoyed reading the posts on this site for some time now, and I am hoping that someone on here would be able to help me out with a problem. We have a small DeviceNet network consisting of a 1756-DNB (node00), two Wago scanners (nodes 03, and 04) and two identical MTS position transducers (nodes 02, and 05). The DNB card is in a rack along with a ControlLogix L71 controller. We have been experiencing random device net error alarms lately where a node would stop communicating and we would power down the system and reboot. The errors would then go away. The other day I decided to use the Networx for DeviceNet to find out what was going on when one of these errors popped up. I found that the device on node 05 was not present on the network. Since we had a spare identical sensor I decided I would address the sensor as node 05 and configure it using a spare DNB card and chassis we have. All went well until I installed the spare sensor into the system. At that point we had alarms pertaining to most of the device net devices. Scanning the network with the Networks software showed no device problems, all were present and communicating, but I could not get the alarms to reset. We tried rebooting the network, the sensor, and even the entire system with no luck. It wasn’t until I reinstalled the old sensor that we were able to get the alarms to clear. Since I have rambled on long enough I won’t bore you with the rest of the trip down this rabbit hole I went down, but what did I do wrong when trying to change this sensor? Is there a specific sequence of events that need to take place when replacing one, even if the sensors are identical?  I am stumped, and we still have the potential of one of these sensors failing without having a clear idea about how to go about changing it. Any help would be greatly appreciated. 

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Welcome to the MrPLC forum community !

The first thing to do when you're dealing with intermittent DeviceNet problems is to check for proper termination resistors (about 60 ohms between blue and white wires, with power off), as well as any obvious loose connectors or an overloaded power supply.

After that, when you're dealing with alarms or errors, pay close attention to the scrolling display on the 1756-DNB.   All that data is also available in the status tags for the module, but a quick look at the scrolling display is a faster way to figure out things like Error 91 (Bus Off) or 92 (No Power).

When plugging in one devices takes down the whole network, then the device is probably a duplicate node to the Scanner, or the Data Rate is set to the wrong value.  

DeviceNet can run at 125, 250, or 500 kb/s.     Most slave devices auto-detect the traffic on the network and adjust themselves, but some can be hard-set for a specific data rate.

Imagine you're having a rap battle and Celine Dion shows up singing "My Heart Will Go On".    It's the same thing with a mis-matched data rate;  the transmissions are at the wrong speed so that they interfere with shorter or longer transmissions and can't use the built-in CAN network anti-collision mechanisms.

MTS has built DeviceNet-equipped position sensors for a long time.   Some of the older ones had the data rate set by DIP switches, and even the modern -R series can be ordered with a pre-set data rate from the factory.    

So a mis-set data rate is my best guess at the problem you were having.     This incident is probably a good prompt for taking a look at the "alarm reset" logic and how it works on your specific system.    Most DeviceNet status or alarm conditions are self-resetting;   when power is restored the Error 92 goes away, and when a slave is reconnected, Error 72 goes away.

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Ken thanks for replying. The network is set for 500 kb/s. The sensor is a R series sensor factory set for 500 kb/s. It came set as node 63 from the factory, so I changed the node to 05.  I guess the revision level of the sensor may have been different than the one previously installed. I thought I could take care of that issue by correcting the identity mismatch after uploading but I never got a message this was the case. The original alarm was an E78 node 05. The alarm handling operates like you suggested, after a few minutes a reset command is issued by the controller and then it issues a run command to the scanner. This was another piece of the puzzle or rabbit hole that has me confused. After switching back to the old sensor, all errors went away but the scanner was stuck in idle mode.  Looking through the controller tags, there were no device net errors and there was a 1 in run status tag but the module still said idle. I could not get the module to switch to the run mode until I downloaded a copy of the program back into the controllogix controller. Then the scanner went into run mode and we have been running this way for a few shifts now. This system has been in place for 17 years now and we have had these alarms happen a couple times a year. This is our first attempt at changing one of the devices, and I thought I had my ducks in a row, apparently I did not. 

 

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E78 tells that node (5) is configured in a scanlist but it is not responding...

did you check terminations and presence of 24V on the bus? is the wiring correct? are ALL devices on same DeviceNet network set to use same speed?

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1756-in566_-en-p.pdf

 

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Not sure if I should start a new thread for a little question here? Thought Id hijack this one ;) Sorry geetee1969.

Installed a new set of e3 plus overloads. Need to connect them to existing DeviceNet. Have two cards, each to a powertap, then to a devicebox. Have three sets connected to devicebox already and need to connect the new set. What steps should I take?

We use to just connect one e3 at a time on a set to node 63 and change it to the next node up and so forth, but havent done a new line to the devicebox yet. How do I get the plc to pickup on the new branch?

Hope this makes sense.

 

Regards

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connected how? what PLC? what software? etc

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Got it sorted. Silly me.

 

Its a AB control logix. Silly me missed the one OL being an older model had to be set manually.

 

Cheers

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