Part IV: Digital Computer Control
So far in the book we have treated only continuous time (or analogue) control systems. However, the reality is that almost all modern control systems will be implemented in a digital computer of one form or another. Thus in this fourth part of the book we will describe the essential differences between analogue and digital control. Some authors devote entire books to this topic. This tends to highlight the differences between analogue and digital control. However, our perspective is quite different. We want to show the reader that these topics actually have a remarkably close connection. We show, for example, that all properly formulated digital controllers converge to an underlying continuous controller as the sampling period goes to zero. We also point to the issues where digital and analogue control are different - especially at slow sampling rates.