Ladder Logic. A more recent evolutionary step is the Programmable Automation Controller (PAC), which is typically programmed in C/C++, and has analog, digital, and communications functions built in. This is the arena where the Arduino (and even a Raspberry Pi) shines. No longer do process controls have to be expensive, proprietary, and mysterious. It's much simpler to control a pump or solenoid with a Arduino, by reading sensors (digital or analog) and writing short pieces of decision code. Data can also be sent by way of ethernet or wifi to a central database. There are even DIN Rail Mounts for mounting your Arduino and Screw shield.
Anyone can build industrial process controls, for very little expense, with very short development times.
Steve Spence builds Arduino based industrial process controls in a manufacturing / factory setting for his employer.