844
FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
37 Error Check Method and Error Code List
37.1 States and Colors of LEDs PLC Operation Status
37.1.3
BATT LED [lit or unlit] [FX
3U
/FX
3UC
]
37.1.4
ERROR LED [lit, flickering or unlit] [FX
3U
/FX
3UC
]
LED status
PLC status
Action
Lit
The battery voltage is low.
Replace the battery as soon as possible.
(Refer to FX
3U
/FX
3UC
Hardware edition.)
Unlit
The battery voltage exceeds the value set in
D8006.
The battery is normal.
LED status
PLC status
Action
Lit
A watchdog timer error has occurred, or
the hardware of the PLC may be
damaged.
1) Change the PLC mode to STOP, and turn ON the PLC
power again.
When the ERROR LED is off, a watchdog timer error
occurred. Take either of the following actions:
-
Review the program, and make sure that the
maximum value (D8012) of the scan time is not larger
than the set value (D8000) of the watchdog timer.
-
Make sure that an input used for input interrupt or
pulse catch does not abnormally turn ON and OFF
several times in one scan time.
-
Make sure that the frequency of the pulse (duty: 50%)
input to a high speed counter is within the
specifications range.
-
Adding WDT instruction
Use two or more WDT instructions in a program so
that the watchdog timer is reset several times in one
scan time.
-
Change the set value of the watchdog timer
Change the set value (D8000) of the watchdog timer in
a program so that it is larger than the maximum value
(D8012) of the scan time.
2) Remove the PLC, and connect another power supply to
the PLC.
If the ERROR LED is off, the cause of the error may be
noise. Examine the following action:
-
Check the wiring for grounding, and then review the
wiring route and installation location.
-
Add a noise filter in the power line.
3) If the ERROR LED is not off even after the step 1) or 2),
consult a Mitsubishi Electric Distributor.
Flickering
Either of the following errors occur in PLC:
•
Parameter error
•
Syntax error
•
Circuit error
Execute the PLC diagnostics and program check by
programming tool.
For the action, refer to Section 37.4.
Unlit
Error which stops PLC is not occurred.
If PLC operation is a failure, execute the PLC diagnostics or
program check by programming tool.
An I/O configuration error, serial communication error or
operation error may occur.