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Unread April 21st, 2010, 01:13 PM   #1
Matthewn
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AB 1747-SDN Devicenet module

Hi All,

I'm having a problem with a 1747-SDN devicenet scanner module. The network which its on is small. Only two other nodes, both partlow PID loop controllers (MLC9000). There had originally been 3 nodes - a speed drive along with the two PID controllers. But we wanted to remove this as we were replacing the drive and were going to use normal analog signals. I did this - using rsnetworx and a 1747 sdnpt driver. I connected to the scanner through the backplane and removed the speed drive from the scanlist. However, the module still shows a fault, the same fault it had been showing all along. The module status light flashes red, the netword light is solid red and error 91 shows up on the screen, a bus-off error if im correct. The network itself seems fine, each end has been terminated with 120ohm resistors, dnet power seems good, shield is grounded, each node has the right baud and node number configured. Could anyone shed some light? Thanks in advance.

Matthew.
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Unread April 21st, 2010, 01:23 PM   #2
highvoltage8471
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Devicenet scanner

Correct me if im wrong and im not sure with device net but isn't there only supposed to be a resistor at one end?
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Unread April 21st, 2010, 01:25 PM   #3
mellis
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You're wrong, resistors should be at both ends of the trunk.
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Unread April 21st, 2010, 01:27 PM   #4
Matthewn
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You could be right, however i did remove the resistor from one end at one stage and the same error was shown. The Scanner is at poistion 1, and both PID controllers at position 2 and 3. So currently I have a resitor accross the blue and white wires at both the scanner at position one and the PID controller at position 2.
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Unread April 21st, 2010, 01:28 PM   #5
Matthewn
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Sorry that should have been the PID controller at position 3.
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Unread April 21st, 2010, 01:32 PM   #6
OkiePC
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Check the power at each node. A bus off condition can mean that your power has dropped below 16 volts somewhere.

Have you cycled power to the rack? You also may need to cycle power to the slave nodes. The error may have occurred when you changed the network wiring and may persist until the scanner is reset, or power cycled.
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It's not all the variables I am most concerned with, it's the undiscovered constants.
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Unread April 21st, 2010, 01:37 PM   #7
Matthewn
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Hi Okie,

Thanks for the reply. Yes, the power was cycled alright. And Dnet power at each node seems fine. I didn't reset the module though, ive never done this. I have an inclination the scanner may be faulty, from the manuals, a solid re network light doesn't sound too good. However, i may be missing something and would like to eliminate any other possible cause before I order a new one.
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Unread April 21st, 2010, 01:57 PM   #8
mordred
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on the remote device reset the power there I get these flashing errors on a regular basis on devicenet have yet to see it not reset.

This may also help I located this to study the requirements after we got the device net surprisingly Its on the AB website as opposed to the Omron website

http://literature.rockwellautomation...m072_-en-p.pdf

to answer the above on how many terminating resisters each end requires it
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Unread April 21st, 2010, 02:08 PM   #9
doctord
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Here is a Rockwell DNET troubleshooting guide that might help. Verify that all nodes have different addresses and if any has a built-in termination resistor.
Attached Files
File Type: pdf DNET TROUBLE SHOOTING GUIDE.pdf (219.5 KB, 68 views)
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Unread April 21st, 2010, 02:28 PM   #10
Matthewn
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Hi Doctord,

Thanks for the reply. I Had a look through the manual. Nothing that could be a problem popped out. I'm pretty confident the physical network is good. That leaves me with a configuration problem which would cause the fault indications to show as they do, a faulty scanner or something else entirely different that I havent considered.
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Unread April 21st, 2010, 03:47 PM   #11
mordred
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theres the other guide I was looking for lol I lost the link and it was too big to post thank Ya saved this link now. One thing that popped out is the mention of fault code 91 associated with baud rates.

The module status light flashes red, the netword light is solid red and error 91 shows up on the screen, a bus-off error if im correct



Blinking
RED means no communication
Check for missing power on all nodes
Check if all other nodes are disconnected
Check node baud rate ( Bad baud rate does not always cause buss off )
Check scanner, if a code 91 is displayed then the communications connection with the node
has timed out. Recycle 24V supply and then reset scanner.

this was in the second posted article on troubleshooting though easily missed as its written in much smaller lettering

Last edited by mordred; April 21st, 2010 at 04:26 PM.
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Unread April 21st, 2010, 04:31 PM   #12
mordred
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on page 5-3 of the first manual I posted there is a section on faults and possible causes check those out
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Unread April 23rd, 2010, 12:56 AM   #13
highvoltage8471
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yes I had this problem disconnecting a robot connection. I don't know if this pertains but I had to reconfigure the scanner for the missing node. Also check all the other nodes that are presently connected, and reset them one at a time to make sure they are all communicating.
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