In industrial automation you are not supposed to do anything at 50Hz, the reasoning is simple: more times than not you are simply turning on and off something t

In industrial automation you are not supposed to do anything at 50Hz, the reasoning is simple: more times than not you are simply turning on and off something that is AC powered and you do that probably with mechanical relays and contactors, quite obviously it is pointless to do that faster than some multiple of AC line period. It is simply about trusting the supplier, certifications and perceived reliability of the thing. On the other hand even brand name PLC hardware is not that expensive if you factor in the fact that interfacing with 24V and mains-level logic is somewhat complex engineering problem. Relays and optocouplers are expensive. Edit: and as for what PLCs can do that random MCU cannot: the Chinese Mitsubishi GX/FX clones mentioned in the sibling thread are essentially STM32 eval boards with industrial I/O and preloaded PLC firmware, nothing more, nothing less, so there you go.