Epson RC620 Manual page 157

♦ Causes of Error
Possible Cause
 Disconnected
terminating resistors
 Cable disconnection
 Disconnected
connector
 Disconnected signal
wire
 Loose connector
 Loose signal wire
 Voltage drop of
communications
power supply
 Noise
(external cause)
 Broken unit
 No cause is
identified.
RC620 Option Fieldbus I/O Rev.8
Examination Method
(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
 Measuring point: Connection
of the trouble unit
 For details, refer to the
section 4.1.3.1 Connection
Problem.
Check for the connection of
connectors and signal wires.
→ The connectors and signal
wires should be firmly
connected.
 Checkpoint: all nodes and all
branch taps
 For details, refer to the
section 4.1.3.2 Loose
Connector and Signal Wire.
Measure voltage of
communications power supply
at the unit with a trouble.
→ Normal: 11V or more
between V+ and V-
 If the voltage is 11 to 14 V,
the unit is a possible cause.
Fix the problem on the unit.
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.
Replace the broken unit with a
new one.
→ Verify whether the problem
is fixed.
Identify the trouble point by
dividing the network.
→ For details, refer to the
section 4.1.3.4 Broken Unit
Examination.
4. Troubleshooting (DeviceNet)
Countermeasure
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.
Connect the connectors and
signal wires again.
Check the voltage of the
power supply.
Calculate the current
capacity of the cable and add
more communications power
supplies.
Take countermeasures
against noise.
Replace the unit with a new
one.
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