Understanding error handling
Errors can kill the execution of a program, which, in turn, can lead to injury or death. A fatal error will halt the execution of a program. These fatal errors are typically called exceptions. Essentially, an exception occurs when the PLC encounters a problem that it cannot handle at runtime. The ultimate fate of the PLC when an unhandled exception occurs is the program locking up and the PLC needing a reboot. On top of all that, if the condition that caused the error originally occurs again, the program will crash again, and the system will need to be rebooted. In essence, the only safe way to handle the condition is to modify the code to ensure that the condition does not happen again.
Exception errors will not show up during the compilation process. Instead, exceptions occur when the program is running. Due to their nature, it is often difficult or impossible to fully predict when an exception will occur. To make matters worse, some exceptions can...