DACs sense nonsense and loopy loops

Abstract: A discussion of Process Logic Controllers (PLC) and proportional, integral, and derivative (PID) control. To some the thought of an analog control loop is difficult, and the concept of loop stability is considered fragile. Somehow the concept of a \"digital loop\" or \"analog loop\" is mildly amusing. A control loop controls something independent of how it is implemented, analog or digital. Control loops do just as say, they control. The loops fall into two broad areas they can be open or closed. We will touch on the topic just enough to define the DAC parameters necessary in different control situations and to select such from datasheets.