Batching process like Soup is a good one, this will improve your skills.
Think about designing (on Paper) a simple batching process.
For example:
You have a vessel with load cells, therefore you need to process the data from them into a meaningful measurement i.e. kg, think about the recipe structure, this could be quite simple i.e. most PLC's now have enough memory to store a few recipes, what additions do you need, i.e. water, oil, manual addition like veg or meat, perhaps an emulsion (starch), mixing times/speeds of agitators, heating blending (perhaps shear mixers), batch sampling, discharge to a cooling vessel then the cooling cycle i.e. vacuum or glycol cooling, transfer to bins or vessels ready for production.
Design your process plant i.e. how many valves, motors, inverters for speed settings, heating loops i.e. jacketed steam, have flexible recipe structure i.e. all recipe stages are almost the same contain things like weight to be added, does it require mixing & blending, heating times etc.
the recipe may contain a field that dictates the type of addition, i.e. water milk, emulsion, manual addition, heating & mixing only etc. that way each stage is the same it's just the variables that are enabled & the product type.
here is a simple one.
Recipe stage:
Type of addition (0-4) 0= no addition, 1 = manual addition, 2 = water etc.
Mixer required (0-1) yes/no
Heating required (0-1) Yes/no
Blend required (0-1) yes/no
Mix time
Temperature
etc.
This will give you a good grounding, for many of the types of code you need to produce i.e. analogs, digital I/O, maths sequences.
Easy to simulate as you can write extra blocks for the simulation of valves opening/closing, incrementing/decrementing the weight & heating etc.
handling of recipes.
If you think this is probably too advanced then perhaps a simple pick & place system that picks up a drum at a station moves it to an elevator/tipper, raises it, tips it, returns back for next drum.
