Level 1a. Stuff slightly more complicated than a list of settings, usually for something like a VFD or a stepper motor controllers. Not as common.
Level 2 PLCs, HMIs, and the black magic robotic stuff. Stand alone equipment. Like imagine a machine that can take something, heat it up, and give it to the next machine.
Level 3: DCS and SCADA. Data control center and whatever SCADA stands for, I always forget. This is typically for integrating or at least data collection of multiple stand alone equipment for level 2.
Level 4: the integration layer between Level 3 and whatever means the company has for entering in sales.
Like everything in software this is all general. Some places will mix layers, subtract layers, add them. I would complain about the inconsistent nature of it all but without it I would be unemployed
Is this specific software engineering languages? or is this electrical engineering or what kind of work is this?