ABSTRACT
Programmable logical controllers (PLCs) have been in use since the 1960s and are the basis for the low-level control in many automation systems. PLCs can handle not only the lowest levels of control but also advanced control of hybrid systems, where time-driven continuous controllers have to be integrated with event-driven controllers. The state concept is of fundamental importance to understand sequencing control. Switching theory, which provides the foundation for binary control, is used not only in automation technology but is also of fundamental importance in many other fields. This theory provides the very principle on which the function of digital computers is based. In general, binary combinatorial and sequencing control is simpler than conventional feedback control, because both the measurement values and the control signals are binary. However, also binary control has its specific properties that have to be considered in more detail.
