stumped with devicenet

To make a long story short, my company purchase a used conveyor loop, which i seen running 2 months previous. The loop arrived was set-up and commissioned. After 3 people tried to get it running, the task was lastly given to me. After a week of frustration, the system(loop), is partially running.

The system contains 15 nodes on devicenet which contain nordac device modules, holijeron modules, and a compact scanner card. I seem to get all the nodes visible (looking online with rsnetworx for devicenet and rslinx), but some of the modules are not acting like they are communicating with the master(scanner card). The whole system is set at 500k baud and each node is set with dips. The system contains all three devicenet cable types(thick, thin and flat) and there are terminating resistors on both ends.

I'm fairly new with devicenet and rsnetworx for devicenet.

What is the correct procedure to commission a network?

THe system seems to flake out and a node goes bad, i fix it, then 3 more nodes go bad. I'm thinking that im downloading, uploading, and doing my network setups in the wrong order and i keep downloading over my working network.

If its flaky at 500k baud maybe putting it down to 125k baud work help with this?

I have a devicenet media checker, but it seems like it will only work with on media at a time, but i have all three types of media.

I'm at the point where im going to call rockwell and get help.

I've printed out manuals, and read but unless a person if real experienced it doesnt help to much when i dont know the language.

MY eds files are all updated, and my linx is updated.

I'm at a loss, any help would be appreciated.

It has been a while since I dealt with DNET but see if this helps: http://www.odva.org/Portals/0/Library/Publications_NotNumbered/DeviceNet_Troubleshooting_by_Robert_D_Law.pdf
The power supply can be a BIG issue even if you have less then the limited number of nodes, it may be possible you need a dual supply or 2 supplies. I ran into this my first time dealing with it. AS mentioned in that pdf, the power supplie(s) should be for the DNET network ONLY.

Hope this helps, will offer more if I can think of it, maybe others can offer more.

DeviceNet is really not as hard as some people make it out to be, but you absolutely must follow the essential rules for wiring the network.

First, power. Have a good 24VDC power supply that can meet the current needs of all the devices on the network. Dedicate the power supply ONLY to an individual DeviceNet network. Ground the power supply Common termial, and the network shield, at one point (generally at the power supply).

Second, termination. There must be one 120 Ohm terminating resistor at each physical end of the network trunkline.

Not one. Not three. Not 150 ohms. Not 82 ohms. Not 1200 ohms.

Third, network trunk length vs. speed.

The rules are simple: 100 meters at 500 kb/s, 250 meters at 250 kb/s, 500 meters at 125 kb/s.

Fourth, dropline distance.

DeviceNet nodes can be between zero and 20 feet from the trunkline. You can push this a little (25 feet ought to work) but not a lot (40 feet won't.)


The absolute best tool you can have for troubleshooting a DeviceNet is a NetMeter from Woodhead Connectivity. If you get a Rockwell network engineer onsite, he will have one.

There is a PowerPoint slideshow that comes with RSNetworx that illustrates the basics of operating the program. You can find it in your RSNetworx program directory:

C:\Program Files\Rockwell Software\RSNetWorxii\DeviceNetRoadMap.pps


The biggest rookie mistake that I see is that people take an empty project and browse the network, which brings up icons in the graphical view for each device. Then they double-click on a device and immediately and totally ignore the notification box that is displayed.

You see, if you choose "download to device" when you have only created a new project and browsed the network, the RSNetworx for DeviceNet software can only download the parameter values it has stored.... which are the defaults.

When I go online with a new network for the first time, I browse to identify all the nodes, then right-click in blank space on the graphical view and select Upload from Network.

This feature directs the software to go around to each device in the graphical view and upload the current parameters from it. It can take a while, especially over a slow connection, but it's the very best way to capture the current settings for all of your network devices.

There's also a much more potentially dangerous feature, Download to Network. The aforementioned starstruck user who has browsed a new network and chosen "Download To Network" will load each device in turn with the default values from the EDS file. Not necessarily what you want. This is why the E3 overload relays, and many drives, have a "Program Lock" feature to prevent this kind of mistaken default parameter loading.

About all that mixed wiring.... I realize you inherited it, but you're going to have to take it seriously because it has the potential to mess you up.

The flat cable, of course, has no shield. This means that the shielded thick and thin cables have to be considered to be individual segments for noise shielding purposes.

Carefully examine your shielded segments to be sure they're grounded in only one place.

Also, eyeball the cables and be certain they're DeviceNet cables. DNet cable requires a characteristic impedance of 120 ohms, which is not too uncommon, but is also not the default of ordinary untwisted 5-conductor control cables. I have seen countless users install whatever they wanted (including untwisted 14 AWG appliance wire) then appear bewildered when I told them that a high speed digital network might require the correct type of cable.

What exactly are the Nordac and Holjeron modules ? I know Holjeron makes conveyor-specific zone controllers and light-tower/pushbutton type devices, but Nordac is a new name for me.

Regarding the network speed; I generally commission the network at 125 kb/s, take some measurements, then turn it up if performance requires. 125 kb/s is generally more stable and error-resistant than 500 kb/s.

A little googling... Nordac sounds like it's the NORD company's servo controller with a DNet interface.

The most noisy and difficult systems I've ever faced involved servodrives. You have a grounding and shielding project ahead of you.

First, find out if noise is the problem at all. A few minutes with an SST/Woodhead DeviceNet NetMeter will settle that question.

helijeron makes zone control modules for conveyors, just like you said and nordac is a devicenet interface that goes on a motor............thanks for your help.............i have some ideas now

Ken Roach said:

DeviceNet is really not as hard as some people make it out to be, but you absolutely must follow the essential rules for wiring the network.

Click to expand...

That pretty much somes it up. DNET is very sensitive to wiring, power supply, and grounding. If you follow the rules it works fine. If it doesn't work you have broken a rule or you have a bad device. With most networks you can bend the rules a bit and it will still work, in my experience this is not the case with dnet.

Hi Ken,

Thankyou for putting it all in one post. It will help a lot more people than PLC_NEWBIE
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