Types of Errors in PLC

plc

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PLC errors are of two types based on the severity of the errors, Fatal errors and Non-fatal errors. Fatal errors are more serious errors which stop the PLC operation. Non Fatal errors are less serious and don’t stop the PLC operation.

Non-Fatal errors:

PLC operation and program execution will continue after one or more of these errors have occurred. Although the PLC operation will continue, the cause of the error must be corrected and the error occurs be cleared as soon as possible.

When one of these errors occurs, the POWER and RUN indicators will remain lit and the
ERR/ALM indicator will Flash.

The Following messages may appear on the programming console display.

• SYS FAIL FAL**
• SCAN TIME OVER

You need to refer to the appropriate PLC manuals to check the Flags to determine the cause of the problem and correct the error.

Fatal Errors

PLC operation and program execution will stop and all outputs Irom the PLC will be turned OFF when any of these errors have occurred. CPM1A operation can1t be restarted until the PLC is turned OFF and then on again or a Peripheral. The device is used to switch the PLC to PROGRAM mode and clear the Fatal error.

All CPU indicators will be OFF Ior the power interruption error. For all other Fatal operating errors, the POWER and ERR/ALM indicators will be lit. The RUN indicator will be OFF.

The Following messages may appear on the programming console display

• MEMORY ERR
• NO END INST
• I/O BUS ERR
• I/O UNIT OVER
• SYS FAIL FALS**

You need to check the error Ilag oI the appropriate PLC manual to determine the cause of the problem and correct the error.

User-defined Errors

There are three instructions that the user can use to deIine his own errors or messages. FAL(06)
causes a non-Iatal error, FAL(07) causes a Iatal error, and MSG(46) sends a message to the
Programming Console or host computer connected to the PC.

FAILURE ALARM-FAL(06)

FAL(06) is an instruction that causes a non-Fatal error. The Following will occur when an
FAL(06) instruction is executed:

1,2,3… 1. The ERR/ALM indicator on the CPU will Flash. PC operation will continue.
2. The instruction1s 2-digit BCD FAL number (01 to 99) will be written to SR 25300 to
SR 25307.

The FAL numbers can be set arbitrarily to indicate particular conditions. The same number cannot be used as both a FAL number and a FALS number.

To clear a FAL error, correct the cause of the error and then execute FAL 00 or clear the error using the Programming Console.

SEVERE FAILURE ALARM-FALS(07)

FALS(07) is an instruction that causes a Fatal error. The Following will occur when a FALS(07)
instruction is executed:

1,2,33 1. Program execution will be stopped and outputs will be turned OFF.
2. The ERR/ALM indicator on the CPU will be lit.
3. The instruction1s 2-digit BCD FALS number (01 to 99) will be written to SR 25300 to SR 25307.
4. The FALS number and time of occurrence will be recorded in the PC1s error log area. If a Memory Cassette with a clock (RTC) is used.

The FALS numbers can be set arbitrarily to indicate particular conditions. The same number cannot be used as both a FAL number and a FALS number.

To clear a FALS error, switch the PC to Program Mode, correct the cause oI the error, and then clear the error using the Programming Console.

MESSAGE-MSG(46)

MSG(46) is used to display a message on the Programming Console. The message, which can be up to 16 characters long, is displayed when the instruction1s execution condition is ON.