LG Electronics 120S user manual Functions, Self-diagnosis

Chapter 5 Power Supply / CPU

5.6Functions

5.6.1Self-diagnosis

1)Functions

(1)The self-diagnosis function permits the CPU module to detect its own errors.

(2) Self-diagnosis	is carried	out	when an error occurs during PLC power supply	is turned on or operating process.
If an error is	detected,	the	system stops operation to prevent faulty PLC	operation.

2) WDT (Watch dog timer) function

The watch dog timer is an internal timer of a PLC to detect the error of hardware and a sequence program. it is changeable with parameter setting.

The CPU resets the watch dog timer before step 0 is executed (after the END processing is finished). When the END instruction has not been executed within the set value due to an error occurred in the PLC or the delay of a sequence program, the watch dog timer will times out. When a watch dog timer error is occurred, all outputs of the PLC are turned OFF, and the ERR LED of the CPU will flickers. (RUN LED will be turned OFF) Therefore, when use FOR ~ NEXT or CALL instruction, insert WDT instruction to reset the watch dog timer.

Refer the MASTER-K programming manual for details on the parameter setting.

0 WDT END 0 END

WDT Reset WDT Reset WDT Reset

3) I/O module check function

Mounting conditions of the loaded module are checked

4) Error history

When error occurs, Corresponding error code is stored in special relay F006.

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