Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 111)

Publication DNET-UM072C-EN-P - July 2004
Correct and Prevent Network Problems 5-7
Use Terminating Resistors The DeviceNet network may operate unpredictably without terminating
resistors installed at each end of the trunk cable. You can order terminating
resistors, part number 1485A-C2, from your local Rockwell Automation
distributor.
To install terminating resistors:
1. Attach a 121 Ω , 1%, 1/4W or larger terminating resistor at each end of
the trunk cable, across the blue (CAN_H) and white (CAN_L) wires of
the cable.
2. Verify resistor connection.
a. Disconnect DeviceNet power.
b. Measure the resistance across the blue (CAN_H) and white
(CAN_L) wires of the cable. Resistance should equal approximately
50 - 60
Ω. Resistance will approach 50 Ω as more devices are
connected to the network.
Ground the Network You must ground the DeviceNet cable at only one location, closest to the
center of the network.
To ground the network:
1. Using an 8 AWG (10mm
2
) wire up to a maximum of 3m (10 ft.) in
length, connect the following:
a. Connect the network shield and drain wires to an earth ground.
b. Connect the V- conductor (black wire) of the trunk cable to an earth
ground.
c. Connect the DC ground of the power supply to an earth ground.
Diagnose Power Supply
Problems The DeviceNet network requires 24V dc power. Ensure that the power supply
you are using meets the following requirements.
The DeviceNet power supply must:
• be sized correctly to provide each device with its required power
• be rated 24V dc (+/- 1%)
• have its own current limit protection
• have a rise time of less than 250mS to within 5% of its rated output
voltage