Emerson Exchange 365

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Delta V/Devicenet wiring topology

Hello all,

Having come into a situation where the Delta V system was planned and installed by others, I sometimes find myself in the position of trying to determine why things were done a certain way. While my Devicenet network does function in its current configuration, I'm about to add some nodes and have found some issues with the wiring topology. The Devicenet cable originates at the card in the Delta V system, hits the first power supply in the MCC cabinet, and then travels through the cabinet making a drop at each bucket. The first terminating resistor is attached to a tee just past the first power supply and the second terminating resistor is at the end of the trunk line. It seems that the Delta V Devicenet card would be another node and that the first terminating resistor should be attached to a short cable run on the other side of the card such that the order would be resistor, card, power supply, mcc drops, resistor. What I have now is card, power supply, resistor, mcc drops, resistor. Any thoughts, opinions, or criticisms are welcome. Thanks in advance.

Logan J

• 27 Jan 2016 7:59 PM
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6 Replies

• Tracy Waller

  

  • 28 Jan 2016 11:05 AM

  Logan,
  The DeltaV card doesn't have to be at the end of the bus. Picture the bus as a straight line, then picture the devices as hanging off of the bus. Then you should see that the DeviceNet Card is just a device hanging off of the bus... Click here to see the DeviceNet Planning and Installation Manual from ODVA for more info that I've posted in the library in this group.  On page 1-4 is a picture of what I'm talking about...

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• Logan J

  

  • 28 Jan 2016 11:58 AM

  In reply to Tracy Waller:

  Tracy,
  That's what I was thinking as well...the Delta V card is just another node with respect to the wiring topology. I have looked at the ODVA manual and wanted some confirmation from others who had experience with this protocol that I had interpreted it correctly. I looked at some oscilloscope traces yesterday afternoon and, while I'm no expert with that device, did not see clean transitions from dominant to recessive as were displayed in the example traces that I had found. My scope is supposed to be able to decode CANbus but could not read any of the traces that I saved which makes me think I have issues with either noise or reflections on the line. Would you agree then, given that my Delta V card is at the end of the trunk line and there isn't really any way to change its location, that I should add a short piece of trunk line with a terminating resistor to the card? That way I have the resistors on either end of the main line. Thanks for your reply as well.

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• Tracy Waller

  

  • 28 Jan 2016 3:45 PM

  In reply to Logan J:

  I think it should be just fine where it is. Mine is wired just like that. Check to make sure all screws are tight. Check for one and only one ground. Make sure you have 2 terminators by measuring the resistance on the bus...(not three, not one...)

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• Rachelle McWright

  

  • 28 Jan 2016 3:55 PM

  In reply to Tracy Waller:

  Hi Tracy Waller, can you please add the pdf file you reference in this post to the DeltaV Library in this group? This way, folks will be able to view a visual of the attachment. I can also provide a link to the item in the library from your original post. Thanks so much! :)

  Best Regards,

  Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast

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• Tracy Waller

  

  • 28 Jan 2016 4:29 PM

  In reply to Rachelle McWright:

  Done. Also added the troubleshooting guide...

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• Rachelle McWright

  

  • 28 Jan 2016 4:42 PM

  In reply to Tracy Waller:

  Awesome resources, thanks so much Tracy Waller! Please visit the Library/Resources tab in the DeltaV group navigation and/or click on the links below to view & download these valuable resources. :

  • DeviceNet Planning and Installation Manual
    
    
  • DeviceNet Plant for Troubleshooting Guide

  Best Regards,

  Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast

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