Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 108)

Publication DNET-UM072C-EN-P - July 2004
5-4 Correct and Prevent Network Problems
bus traffic problems
•
nodes stop communicating
•
device times out
•
check scanner configuration to ensure scan
rate is set correctly
−
inter-scan/delay scan interval too short
can cause device timeouts
−
inter-scan/delay scan interval too long
can reduce system performance and
make inefficient use of available
bandwidth
•
check change-of-state devices consuming
excessive bandwidth
•
increase production inhibit time or change
these devices to polling, cyclic, or bit strobe
communication
•
check for nodes with excessive bandwidth or
a much-higher than average MAX value
bus power problems
•
nodes near the end of the trunk line stop
communicating after operating normally
•
the network communicates only when the
number of nodes is decreased or the trunk
length is reduced
•
check network power voltage at the node
•
check common mode voltage
•
check for output devices (e.g., contactors)
powered from the network
•
check for interference caused by network
cables routed too closely to high-voltage and
RF lines
•
use an oscilloscope to check the power
supply trace for ripple increasing over time
against the baseline
•
check cables for intermittent operation by
shaking, bending or twisting the suspected
cable or connection and checking
peak-to-peak voltages
shield voltage problems
•
nodes operate intermittently
•
properly configured slave devices are not
detected by the scanner
•
check shield voltage
•
check for additional V- or shield wire
connections
•
check for loose connections (in particular,
field-attachable connections)
•
ensure that only shield and V- wires are
connected together at earth ground and the
power supply
problem symptom do this