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 problem 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 trouble unit.
→ 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.
88 Fieldbus I/O Rev.6