18-05-2012, 12:45 PM
modern control technology
(Delmar) Modern Control Technology--Components & Systems (2nd Ed.).pdf (Size: 6.14 MB / Downloads: 215)
INTRODUCTION
A control system is a collection of components working together under the direction of
some machine intelligence. In most cases, electronic circuits provide the intelligence,
and electromechanical components such as sensors and motors provide the interface to
the physical world. A good example is the modern automobile. Various sensors supply
the on-board computer with information about the engine’s condition. The computer
then calculates the precise amount of fuel to be injected into the engine and adjusts the
ignition timing. The mechanical parts of the system include the engine, transmission,
wheels, and so on. To design, diagnose, or repair these sophisticated systems, you must
understand the electronics, the mechanics, and control system principles.
CONTROL SYSTEMS
Introduction and Background
In a modern control system, electronic intelligence controls some physical process.
Control systems are the “automatic” in such things as automatic pilot and automatic
washer. Because the machine itself is making the routine decisions, the human operator
is freed to do other things. In many cases, machine intelligence is better than direct human
control because it can react faster or slower (keep track of long-term slow changes),
respond more precisely, and maintain an accurate log of the system’s performance.
Control systems can be classified in several ways. A regulator system automatically
maintains a parameter at (or near) a specified value. An example of this is a homeheating
system maintaining a set temperature despite changing outside conditions. A
follow-up system causes an output to follow a set path that has been specified in
advance. An example is an industrial robot moving parts from place to place. An event
control system controls a sequential series of events. An example is a washing machine
cycling through a series of programmed steps.
Closed-Loop Control Systems
In a closed-loop control system, the output of the process (controlled variable) is constantly
monitored by a sensor, as shown in Figure 1.3(a). The sensor samples the system
output and converts this measurement into an electric signal that it passes back to
the controller. Because the controller knows what the system is actually doing, it can
make any adjustments necessary to keep the output where it belongs.