Just one other I remember was a bank of Carl Schnell mixers, the clients spec was to use Eurotherm controllers for all temperature control, this proved to be a real problem as the product turned thixotropic, shallow vessels so as the product rose in temperature the vapour injectors would blow holes through the product, the controllers by their nature would increase the flow, this just made it worse, talked to Eurotherm, they sent out a specialist, no joy, I then removed the controllers, built in a profile of steam flow into the recipes, this worked like a treat, so PID in normal terms is not always the answer, yes I could have built in a profile of flow into the controllers, tried this still a little iffy, my idea worked & it removed another not required piece of equipment & so reduced the possibility of failure.