The PLC fault indicator light ERR usually lights up, indicating that the PLC has an error or fault. The following are some common specific meanings:
Program error:
Syntax error: There are places in the written PLC program that violate the syntax rules of the programming language, such as misspelling of instructions, incorrect parameter settings, missing necessary punctuation marks, etc., which cause the PLC to be unable to correctly parse and execute the program.
Logic error: There are problems with the logical flow of the program, such as incorrect conditional judgment, improper loop control, unreasonable timer or counter settings, etc., which make the program run results inconsistent with expectations and even cause the system to run abnormally.
Data overflow: The data used in the program exceeds the range allowed by the PLC data storage area or variable. It may be caused by reasons such as too large calculation results, mismatched data types, or insufficient allocation of data storage areas, which causes the ERR light to light up.
Subroutine error: If a subroutine is used in the PLC program, there may be problems such as subroutine call errors, missing or incorrect subroutine end flags, etc., which affect the normal execution of the entire program.
Hardware failure:
CPU failure: Problems with the central processing unit of the PLC, such as chip damage, internal circuit failure, overheating, etc., may cause the ERR light to light up. The CPU is the core component of the PLC, and its failure will affect the operation of the entire system.
Memory failure: Problems such as memory module damage, insufficient memory, or memory data confusion may prevent the PLC from storing and reading programs and data normally, which in turn causes failures and causes the ERR light to light up.
Input and output module failure: Input module failure may cause the PLC to be unable to correctly receive external signals, and output module failure may cause the PLC to be unable to control external devices normally. For example, damage to the input point, adhesion of the output relay, or damage to the transistor may cause the ERR light to light up and affect the input and output functions of the system.
Communication module failure: When the PLC communicates with other devices, a communication module failure, poor communication line connection, or incorrect communication protocol setting may cause communication failure, and the ERR light will light up to indicate a communication failure.
Power failure: PLC power supply is unstable, power supply voltage is abnormal, or power module is damaged, which will affect the normal operation of PLC and cause ERR light to light up. Power supply is the basis of PLC operation, and power supply problems may cause a series of failures.
Other problems:
Watchdog timer error: The watchdog timer is used to monitor the running time of PLC program. If the program execution time exceeds the set value of the watchdog timer, it may be due to the program falling into an infinite loop or the execution time is too long, causing the ERR light to flash or light up. At this time, it is necessary to check the logic and execution efficiency of the program to ensure that the program can complete scanning and execution within the specified time.
Environmental factors: Harsh working environment, such as high temperature, humidity, dust, electromagnetic interference, etc., may affect the normal operation of PLC and cause ERR light to light up. PLC usually needs to work in a relatively stable and clean environment. Environmental factors beyond its allowable range may cause hardware failure or program abnormality.
Configuration error: If the system configuration parameters of the PLC are set incorrectly, such as I/O point configuration, communication parameter settings, timer/counter settings, etc., the PLC may not work properly and the ERR light will be on to indicate a configuration error. You need to check and modify the relevant configuration parameters to make them consistent with the actual system requirements.
