It has strong self-checking and protection functions.
①Fault detection – The software regularly detects the external environment, such as power failure, undervoltage, low lithium battery voltage and strong interference signals. for timely processing.
②Information protection and recovery – when the occasional fault condition occurs, the information inside the PLC will not be destroyed. Once the fault condition disappears, it can return to normal and continue the original program operation. Therefore, when the PLC detects a fault condition, it immediately stores the current state in the memory, and the software cooperates to seal the memory, prohibiting any operation on the memory to prevent the stored information from being flushed.
③Set the watchdog WDT (watchdog) – If the execution time of each cycle of the program exceeds the time specified by the WDT, it indicates that the program enters an infinite loop and immediately alarms.
④Strengthen the inspection and verification of the program – once the program is wrong, it will immediately alarm and stop the execution.
⑤ Battery backup for programs and dynamic data – after a power failure, the backup battery is used to supply power, and the relevant status and information will not be lost.
One of the PLC factory test items is the anti-interference test. It is required to be able to withstand interference pulses with an amplitude of 1000V, a rise time of 1nS and a pulse width of 1μS. Generally, the mean time between failures can reach hundreds of thousands to tens of millions of hours; the system can also reach 40,000 to 50,000 hours or even longer.
