Random DeviceNet Nodes dropping off Network

Join Date
Jul 2007
Location
Kiruna
Posts
600
Hi Guys,

Very strange one I've encountered that I need assistance with.

I have an CLX L-61 with 2 1756-DNB DeviceNet scanners. Every so often (approx 2-3 times per hour)a random node will dissapear off the network. It occurs mostly on Network 2 but very occasionally on network 1.

There are 55 nodes on each network comprising of DNY41R Starter Auxilarys and E3Plus Overloads. It is ALWAYS an E3 Plus that falls off network. An Error 78 will appear on relevent scanner module for 40-41 seconds every time.

I have an Alarm/Event log on my HMI which logs communications errors and this verifys my problem. Random nodes disppearing off network for exactly 41 seconds!!!!

I'm satsified that network cable lengths are well within spec, properly shielded and terminated. Power supplies are as recommended and DNet voltage levels are correct.

The baud-rate is at 125kps and I have tried increasing this to 250kps with no success.

Has anyone ever experienced this? Any suggestions on how to diagnose this problem would be great.
 
The only time I've every had any nodes "drop off" the network it has usually been one of two things:
a) A cable issue (bad connection, inadequate shielding, etc)
or
b) Power supply issues (power supply breaking down, not big enough, transient voltages, etc)

If you have one available, put a devicenet meter on the system and let it monitor activity for a while, it'll usually point you in the right direction.
 
When you are increasing the baud rate, are you increasing it just for the affected devices or the whole network? If you do this, every device needs to be changed as well as the scanner. I know you said that you verified all of the cables, but that is sometimes difficult to do. I have had faulty cables right out of the bag. The RSNetworks for device net has a feature that troubleshoots your network but it is a seperate purchase from the software itself. Beyond that, 55 nodes seems a bit high. Rockwell states that you can have a max of 63, but that is a best case scenerio. I would first bump the baud rate up to 500. If that fails, I would add a third scanner card to remove some of the burden of the networks.
 
DeviceNet Monitor?

Don't have one readily available. Is it a good investment? I'll look into one tomorrow.

MartB said:
The only time I've every had any nodes "drop off" the network it has usually been one of two things:
a) A cable issue (bad connection, inadequate shielding, etc)
or
b) Power supply issues (power supply breaking down, not big enough, transient voltages, etc)

If you have one available, put a devicenet meter on the system and let it monitor activity for a while, it'll usually point you in the right direction.
 
I have no idea how much they are, I've had one here for a while (I didn't buy it), but I would say it's a good investment (we've used it out in the field mostly), it will report errors and recommend the appropriate fixes. Ours will also monitor for several hours and warn if the voltage went out of range etc.
I'll dig it out and get a part number for you when I can get a minute.
 
Concidering your problem is specific to the E3 Plus I would look to that device and its corosponding EDS file for your problem. We have many networks here with over 55 nodes and have never experenced an error 78 unless there was a specific problem with the device on that node. Like moisture etc. are all the devices autobaud? If so I would try very hard to get the scanner at 500 baud.If this was Ethernet or Controlnet I would suggest scheduling but im not sure you can schedule devicenet. Look carefully at the parameters of the E3 and contact manufacture for that device.

Also we have the devicenet meter and have never found a good use for it because common sense usually worked as good. In your case though it may be usefull.
 
Yes all devices are on autobaud.I have many other Networks on MCC's on other parts of the plant with same Rev of E3 Plus and have experienced no errors. Also on this L-61 Chassis I have 2 more DNet networks with no communication errors. This really is strange.

Even if noise were the issue surely it would effect other networks????
 
My guess is your buss traffic is too high. I had a similiar problem once and was able to get a hold of a Woodhead NetAlert to diagnose that it was a high buss traffic problem. I was able to get down to the 80% buss traffic by reconfiguring DBN module to scannimg many of the nodes using COS/Cyclic and polling background instead of every scan polling.
 
I believe DaveW is on the right track. The NetAlert meter will tell you your traffic loading. If it gets to 90%, you will have the issue you are describing. A simple fix is to increase the Interscan delay. Default is 10 msec, I always set mine to 50 msec. This will typically bring bus traffic down from 60% to 20% running at 500 baud and approximately 40 nodes.
 
We have many networks with large numbers of E3+ overloads installed and they are extremely reliable. We have had problems with large networks losing nodes at low baud rates as the total scan time is high and individual nodes can time out if there are any errors requiring retries. For this reason I would normally run any network at 500K if this is possible.
I would also look carefully at your power supply as the E3's consume quite a bit of power and we normally split our network power into two or three sections to overcome cable volt drops.
It is also worth stressing that the DeviceNet cabling must have the 0v line and the shield connected to ground as failure to do this is the biggest single cause of problems that I see.
Andybr
 
Though we have less nodes than you ( we have 28) we use ferrite beads at input and output of every E3, we have experienced no problems due to noise. Noise could be your problem.
 
55 Nodes on 1 network, I wouldn't even try that when I designed it.
I have started up a lot of devicenet, never seen 55 nodes.
 
Third party verification

A lot of our costumers require us to verify the D-Net through a third party source. One of the third party sources we use is good old Rockwell. Our costumers require this third party to verify the D-Net for many different items, including noise, line loss, voltage drops, power supply grounding, Trunk & drop cable lengths, COS communication on simple devices and Polled on larger (more than 1 32bit word) and so on. They use a D-Net meter and digital scope. They help you with any of the little problems you may have. The report is very complete check list including the scope and meter readings. Just a thought, a thrid party may help you out of a sticky problem.

Bud
 

Similar Topics

Random DeviceNet "Port 5 Adaptor " Fault on various PowerFlex 70 Drives in Panel Good Evening , We have a machine with about 17 -...
Replies
12
Views
14,227
Hi, customer woke me up today with strange problem. He got machine controled by SLC 500 with DeviceNet network (some inverters and Remote IOs...
Replies
10
Views
6,986
The last two days our automation has just stopped randomly at different spots. Everything that has stopped, is thru DeviceNet.We have about 5...
Replies
3
Views
2,607
Looking for some advice for backing up the programs on a bunch of old random PLCs. All I'm really concerned about is getting the program out of...
Replies
43
Views
4,596
We have several Powerflex 4M (22F-D013N114) VFD’s controlled by compactlogix PLC’s. Control is simple, a run and direction signal with the speed...
Replies
6
Views
1,486
Back
Top Bottom