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4. Troubleshooting (DeviceNet)
♦ Causes of Error
Possible Cause Examination Method Countermeasure
{ Disconnected
terminating resistors
{ Cable disconnection
{ Disconnected
connector
{ Disconnected signal
wire
(1) Check that terminating
resistors are connected to
both ends of the network.
(2) Measure resistance
between signal wires with
communications power
supply OFF.
→ Normal: 50 to 70 Ω
z Measuring point: Connection
of the trouble unit
z For detail, refer to the section
4.1.3.1 Connection Problem.
Fix the problem.
How to find the trouble
point:
Remove the terminating
resistor on one end of the
network. The trouble point
is where resistance changes
from 120 Ω.
{ Loose connector
{ Loose signal wire
Check for the connection of
connectors and signal wires.
→ The connectors and signal
wires should be firmly
connected.
z Checkpoint: all nodes and all
branch taps
z For details, refer to the
section 4.1.3.2 Loose
Connector and Signal Wire.
Connect the connectors and
signal wires again.
{ Voltage drop of
communications
power supply
Measure voltage of
communications power supply
at the unit with a trouble.
→ Normal: 11V or more
between V+ and V-
z If the voltage is 11 to 14 V,
the unit is a possible cause.
Fix the problem on the unit.
Check the voltage of the
power supply.
Calculate the current
capacity of the cable and add
more communications power
supplies.
{ Noise
(external cause)
Check the noise intrusion via
the following paths (1) to (3).
(1) Noise via DRAIN (FG)
(2) Induced noise via
communication cable
(3) Communications power
supply
→ For details, refer to the
section 4.1.3.3 Noise
Intrusion.
Take countermeasures
against noise.
{ Broken unit Replace the broken unit with a
new one.
→ Verify whether the problem
is fixed.
Replace the unit with a new
one.
z No cause is
identified.
Identify the trouble point by
dividing the network.
→ For details, refer to the
section 4.1.3.4 Broken Unit
Examination.
Fieldbus I/O Rev.6 85