Programmable Logic
Controllers
Version 0.00
EP 41028 / EP 42028
Prepared by: Dr. Soe Naing
PREFACE
The PLC system is the major key in the technology and industrial sector today. The
PLC system is primarily used to control machinery. A program is written for the PLC
which turns on and off outputs based on input conditions. A PLC is designed to be
programmed once, and run repeatedly as needed.
PLCs can work as standalone units that can continuously monitor and automate a
process, specific machine function. PLCs can be networked; such a network can
control an entire production line. PLCs can be adapted to monitor and control many
sensors and actuators; they process electrical signals and use them to carry out
preprogrammed commands for almost any application.
PLCs are used in industrial automation to increase reliability, system stability and
performance, minimizing the need for human operators and the chances of human
error. This system is responsible for all the growth in industry, manufacturing process,
and even entertainment. That’s why PLC system is very important and needed by all
kinds of industry.
The text is mainly a compilation of the best fundamental essence from the two books:
Programmable Logic Controllers (5th edition) written by Frank Petruzella and
Programmable Logic Controllers Principles and Applications (3rd edition) written by
John W. Webb and Ronald A. Reis. The text covers the basics of programmable logic
controllers in a manner that complements instruction with FX PLC platform. The
underlying PLC principles and concepts covered in the text are common to most
manufacturers. They serve to maximize the knowledge gained through on-the-job
training and programs offered by different vendors. The text is written in an easy-to-
read style that is designed for students with no prior PLC experience.
Each chapter begins with a brief introduction outlining chapter coverage and learning
objectives. Chapters conclude with a set of review questions/ problems. The questions
are closely related to the chapter objectives and require students to recall and apply
information covered in the chapter. The problems range from easy to difficult, thus
challenging students at various levels of competence.
TABLE OF CONTENTS
Page
PREFACE i
TABLE OF CONTENTS ii
CHAPTER TITLE
1 PLC: An Overview 2
1.1 Programmable Logic Controllers 2
1.2 Parts of a PLC 2
1.6 PLC Size 5
1.7 The PLC as a Computer 7
2 The PLC: A Look Inside 9
2.1 I/O Section 9
2.2 Discrete I/O Modules 9
2.2.1 Discrete Input Modules 9
2.2.2 Discrete Output Modules 11
2.2.3 Sinking and Sourcing 12
2.3 Analog I/O Modules 16
2.3.1 Analog Input Scaling 17
2.6 The Central Processing Unit 21
2.6.1 The Processor 22
2.7 Memory Types 21
2.8 Memory Size 25
2.9 Power Supplies 27
3 Number Systems and Codes 31
3.1 Decimal System 31
3.2 Binary System 31
3.3 Negative Numbers 33
3.4 Octal System 34
3.5 Hexadecimal System 35
3.6 Binary Coded Decimal (BCD) System 37
3.7 Gray Code 38
3.8 ASCII Code 41
3.9 Parity Bit 42
3.10 Binary Arithmetic 43
3.11 Floating Point Arithmetic 46
4 Fundamental of Logic 52
4.1 The Binary Concept 52
4.2 AND, OR and NOT Functions 52
4.3 Boolean Algebra 55
4.4 Developing Logic Gate Circuits from Boolean Expressions 56
4.5 Producing the Boolean Equation for a Given Logic Gate Circuit 57
4.6 Hardwired Logic versus Programmed Logic 58
4.7 Programming Word Level Logic Instructions 61
5 Basics of PLC Programming 67
5.1 Processor Memory Organization 67
5.2 Program Scan 70
5.3 PLC Programming Languages 72
5.4 Bit-level Logic Instructions 73
5.5 Ladder Diagram and Instruction Addressing 76
5.6 Branch Instructions 77
5.7 Internal Relay Instructions 80
5.8 Programming Examine If Closed and Examine If Open 81
Instructions
5.9 Entering the Ladder Diagram 83
5.10 Modes of Operation 86
6 Developing Fundamental PLC Wiring Diagram and Ladder Logic
Program (Part 1: The Operation of I/O Field Devices) 92
6.1 Electromagnetic Control Relays 92
6.2 Contactors 93
6.3 Motor Starters 95
6.4 Manually Operated Switches 98
6.5 Mechanically Operated Switches 100
6.6 Sensors 103
6.6.1 Proximity Sensors 103
6.6.2 Magnetic Reed Switch 105
6.6.3 Light Sensors 106
6.6.4 Ultrasonic Sensors 111
6.6.5 Strain/Weight Sensors 111
6.6.6 Temperature Sensors 112
6.6.7 Flow Measurement 114
6.6.8 Velocity and Position Sensors 115
6.7 Output Control Devices 117
6 Developing Fundamental PLC Wiring Diagram and Ladder Logic
Program (Part 2: Contact and Coil Programming Examples) 123
6.8 Seal-In Circuits 123
6.9 Electrical Interlocking Circuits 124
6.10 Latching Relays 130
6.11 Converting Relay Schematics into PLC Ladder Programs 134
6.12 Writing a Ladder Logic Program Directly from a Narrative
Description 137
7 Programming Timers (Part 1: Basic Program Examples) 148
7.1 Latched Circuits 148
7.2 Conditional Control 150
7.3 Interlock Control 150
7.4 Sequential Control 151
7.5 Oscillating Circuit 151
7 Programming Timers (Part 2: Basic Operation of Timers) 152
7.6 Mechanical Timing Relays 152
7.7 PLC Timers 153
7 Programming Timers (Part 3: Basic Design Examples) 158
7.8 Oscillating Circuit with Timers 158
7.9 Flashing Circuit 158
7.10 Trigger Circuit 159
7.11 Off-delay Circuits 160
7.12 One-shoot Timer 161
7.13 Output delay Circuit 162
7.14 Timing Extension Circuit 162
8 Programming Counters
(Part 1: Basic Operation of PLC Counters) 167
8.1 Basic PLC Counter Operation 167
8.2 PLC Counter Simulations 168
(Part 2: Counter Design Examples) 171
8.3 Counter Design Examples 171
9 Program Control Instructions 178
9.1 Hardwired Master Control Relays 178
9.2 MC and MCR Function 179
9.2.1 Simulation for the Operation of MC and MCR 182
9.2.2 Example: A Ladder with a Common Line 183
9.3 The Conditional Jump Function, CJ Function 185
9.4 CALL Subroutine Instruction (CALL, SERT) 187
10 Data Manipulation Instructions 191
10.1 What are Data Registers? 191
10.2 Why we use Timer with Data Registers 193
10.3 The Move Instructions 194
10.3.1 Moving Individual Values with MOV Instruction 194
10.3.2 Moving Group of Bit Devices 196
10.3.3 Moving Blocks of Data with the BMOV Instruction 198
10.3.4 Copying Source Devices to Multiple Destinations 199
10.4 Conversion Transfer Instruction (BCD/BIN) 200
10.5 Data Comparison with CMP Function 202
10.6 Zone Comparison with ZCP Function 203
10.7 Contact Comparison Instructions 203
11 Math Instructions 207
11.1 Arithmetic Operations (ADD, SUB, DIV, MUL) 207
11.2 Simulations for Math Functions 209
REFRENCES 213
