In Helsinki during a visiting lecture, an internationally well-known professor in communica-
tionssaid,‘Inthecommunicationssocietywehavemanagedtoconvertourproposalsandideas
to real products, not like in the control engineering society. They have very nice papers and
strong mathematics but most of the real systems still use the old PID controllers!’. As our
background is mainly in control as well as communications engineering, we know that this
thought is not very accurate. We agree that most of the practical controllers are analog and
digital PID controllers, simply because they are very reliable and able to achieve the required
control goals successfully. Most of the controllers can be explained in terms of PID. The
reasons behind this impressive performance of PID will be explained in Chapter 2.
