Microcontroller system or PLC system
You can buy some quite dumb PLCs, that will only handle a few inputs, outputs and lines of ladder logic, and some really quite clever ones, that are a Pi class or better processor inside, with storage and a nice GUI. 

A PLC is a product that is targeted to a very specific and limited application space, it's not a general purpose computer.

The advantage of a PLC is it's 'industry ready', already in a tough box with protected I/Os, and easy to duplicate if you need more systems.

The problem with a PLC is whether it provides an adequate API, or whether you can 'get into' the software to do what you want. You may find an interface that's been crippled to do exactly what it's advertised to do and no more. I know my TV recorder is just a processor running Linux inside, but I can't get it to do more than the interface presents (won't copy MP3s from a USB for instance) without nuking it and installing a bare OS. 

The question is, do you want to ruggedise a Pi, or find a PLC that you can have your wicked way with?