Programmable Logic Controller (PLC) software measures:

We have a strong self-test and protection.
① fault detection - software periodically to detect the external environment, such as a power failure, under voltage, battery voltage is too low and strong interference signals. So that timely treatment.
② Information Protection and Recovery - When sporadic fault condition occurs, does not destroy the plc cpu modules's internal information. Once the fault condition is removed, you can return to normal, continue the original program of work. Therefore, intelligent plc when the fault condition is detected, immediately put the current state stored in the memory, software with the memory is closed to the memory of any action to prevent the storage of information is obliterated.
③ Set the Watchdog WDT (Watchdog) - If the program execution time per cycle than the WDT specified time, indicating the program into an infinite loop, call the police.
④ strengthen inspection and verification procedures - once the program is wrong, call the police, and stops executing.
⑤ the program and dynamic data backup battery - after a power outage, use battery-powered back-up, and information about the status will not be lost.
Plc modules factory pilot project, there is an immunity test. It is required to withstand the amplitude of 1000V, the rise time 1nS, a pulse width of the pulse 1μS of interference. In general, the average time between failures of up to hundreds of thousands - tens of millions of hours; the system can be made up to 4 to 50,000 hours or longer.