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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 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

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