Page 28 - Modern Control Systems

2 Chapter 1 Introduction to Control Systems

1.1 INTRODUCTION

Engineering is concerned with understanding and controlling the materials and
forces of nature for the benefit of humankind. Control system engineers are con-
cerned with understanding and controlling segments of their environment, often
called systems, to provide useful economic products for society. The twin goals of
understanding and controlling are complementary because effective systems con-
trol requires that the systems be understood and modeled. Furthermore, control en-
gineering must often consider the control of poorly understood systems such as
chemical process systems. The present challenge to control engineers is the model-
ing and control of modern, complex, interrelated systems such as traffic control sys-
tems, chemical processes, and robotic systems. Simultaneously, the fortunate
engineer has the opportunity to control many useful and interesting industrial au-
tomation systems. Perhaps the most characteristic quality of control engineering is
the opportunity to control machines and industrial and economic processes for the
benefit of society.
Control engineering is based on the foundations of feedback theory and linear
system analysis, and it integrates the concepts of network theory and communica-
tion theory. Therefore control engineering is not limited to any engineering disci-
pline but is equally applicable to aeronautical, chemical, mechanical, environmental,
civil, and electrical engineering. For example, a control system often includes elec-
trical, mechanical, and chemical components. Furthermore, as the understanding of
the dynamics of business, social, and political systems increases, the ability to control
these systems will also increase.
A control system is an interconnection of components forming a system configu-
ration that will provide a desired system response. The basis for analysis of a system
is the foundation provided by linear system theory, which assumes a cause-effect re-
lationship for the components of a system. Therefore a component or process to be
controlled can be represented by a block, as shown in Figure 1.1. The input-output
relationship represents the cause-and-effect relationship of the process, which in turn
represents a processing of the input signal to provide an output signal variable, often
with a power amplification. An open-loop control system uses a controller and an ac-
tuator to obtain the desired response, as shown in Figure 1.2. An open-loop system is
a system without feedback.

An open-loop control system utilizes an actuating device to control the process
directly without using feedback.

FIGURE 1.1 Input Process Output
Process to be
controlled.

FIGURE 1.2
Open-loop control Desired output
system (without Controller Actuator Process Output
feedback). response