Devicenet troubleshooting

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DeviceNet Troubleshooting
DeviceNet will not function correctly if design rules are not followed. Even a Network previously thought to be functioning correctly may begin to exhibit abnormal or anomalous operation due to incorrect system design. The following are tips to help locate and correct these abnormalities. For specific DeviceNet System Installation Information. Please refer topublication DN-6.7.2 entitled "DeviceNet Planning and Installation Manual". Manuals can be ordered via the Automation Bookstore on the Internet at " www.theautomationbookstore.com " or your local Allen-Bradley distributor or sales office.

Termination Resistors:
A termination resistor equal to 121 Ohms 1% , 1/4W must be attached at each end of the Trunk cable. The resistors must be connected across theBlue & White wires of the DeviceNet cable. Resistor connection can be verified by disconnecting DeviceNet power and measuring the resistance across the Can_H & Can_L lines (Blue & White Wire). This reading should be approximately 60 Ohms. Important: The DeviceNet network will not operate correctly without terminating Resistors. Termination resistors can be ordered from your local Allen-BradleyDistributor using the part number 1485AC2.

Network Grounding:
The DeviceNet cable must by grounded at only one location. This should be done closest to the center of the network. connect the network Shield and Drain wire to an earth ground using #8 AWG wire up to a maximum 3m ( 10Ft ) in length.Also connect the V- conductor ( Black Wire) of the network trunk cable and the DC ground of the powersupply to this ground connection.

Power Supplies:
DeviceNet requires 24VDC. Use a power supply rated 24VDC (+/- 1% ). Make sure the power supply has it's own current limit protection. Provide fuse protection for each segment of the cable system. DeviceNet requires a power supply to have a rise time of less then 250mS to within 5% of its rated output voltage. The power supply must be sizedcorrectly to provide each device with its required power. Important: The power supply should be used to power the DeviceNet network only.When multiple power supplies are required, verify that the V+ connection is broken between the supplies. Please refer to the " DeviceNet Planning and Installation Manual " for more specific installation procedures.

Examine the System Design of the InstallationWalk the network if possible to determine the actual layout. ( Make a sketch of the network ) Check number of nodes Check cumulative drop length Check individual drop lengths Check branched drop length Check total trunk length, including long drop near the ends Check the termination location and measure the terminators Check the power supply cable length and gauge Check for one, and only one, earthground of the V- and shield Break the combination shield/V- connection to frame ground and verify >1.0 Mohm to frame ground Check for one and only one V- to shield connection Break the shield/V- connection at the power supply and verify >1.0 Mohm shield to V- with 24VDC off Check for shorts of CAN- and/or CAN+ to shield or V- verify with an OHM meter Check the length and gauge of the earth groundconnection Check total power load and its distribution points

Check the Power
Check trunk and drop current limits Check type (size and length) of cable bringing power into the trunk Measure the 24V supply at the middle and ends of the network Consider spot checking the power for noise with an oscilloscope

The 24 VDC Network Power for DeviceNet Must be for the DeviceNet network only.Check the Wiring
Check lead dress in junction boxes Check that connectors are screwed together tightly Check that glands are screwed tightly Check for foreign material (electrical tape, RTV, etc.) in glands Check that nodes are not touching extremely hot or cold surfaces Check that cables are kept a few inches away from power wiring Check that cables are not draped on electric motors, relays,...
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