Automating Manufacturing Systems - Process Control and ...

plc wiring - 1.1
PREFACE
Designing software for control systems is difficult. Experienced controls engineers
have learned many techniques that allow them to solve problems. This book was written to
present methods for designing controls software using Programmable Logic Controllers
(PLCs). It is my personal hope that by employing the knowledge in the book that you will
be able to quickly write controls programs that work as expected (and avoid having to
learn by costly mistakes.)
This book has been designed for students with some knowledge of technology,
including limited electricity, who wish to learn the discipline of practical control system
design on commonly used hardware. To this end the book will use the Allen Bradley ControlLogix
processors to allow depth. Although the chapters will focus on specific hardware,
the techniques are portable to other PLCs. Whenever possible the IEC 61131
programming standards will be used to help in the use of other PLCs.
In some cases the material will build upon the content found in a linear controls
course. But, a heavy emphasis is placed on discrete control systems. Figure 1.1 crudely
shows some of the basic categories of control system problems.
CONTROL
CONTINUOUS
DISCRETE
LINEAR NON_LINEAR CONDITIONAL SEQUENTIAL
EVENT BASED
e.g. MRAC
TEMPORAL
e.g. PID
BOOLEAN
e.g. FUZZY LOGIC
e.g. COUNTERS
EXPERT SYSTEMS e.g. TIMERS
Figure 1.1
Control Dichotomy
• Continuous - The values to be controlled change smoothly. e.g. the speed of a car.
• Logical/Discrete - The value to be controlled are easily described as on-off. e.g.
the car motor is on-off. NOTE: all systems are continuous but they can be
treated as logical for simplicity.
e.g. “When I do this, that always happens!” For example, when the power
is turned on, the press closes!
www.PAControl.com