TABLE OF CONTENTS The advances made in microprocessors, microcomputers, and digital signal processors have accelerated the growth of digital control systems theory. The discrete-time systems are dynamic systems in which the system-variables are defined only at discrete instants of time.
The terms sampled-data control systems, discrete-time control systems and digital control systems have all been used interchangeably in control system literature. Strictly speaking, sampled-data are pulse-amplitude modulated signals and are obtained by some means of sampling an analog signal. Digital signals are generated by means of digital transducers or digital computers, often in digitally coded form. The discrete-time systems, in a broad sense, describe all systems having some form of digital or sampled signals.
Discrete-time systems differ from continuous-time systems in that the signals for a discrete-time systems are in sampled-data form. In contrast to the continuous-time system, the operation of discrete-time systems are described by a set of difference-equations. The analysis and design of discrete-time systems may be effectively carried out by use of the z-transform, which was evolved from the Laplace transform as a special form.
Figure 2.1 (a) shows the block-diagram of a sampled-data control system. The continuous error-signal e (t) is sampled at an interval of time T by means of a sampler. The plant output is also a continuous-signal and it is due to the fact that a hold circuit preceeds the plant.
