Programmable Logic Controllers

Dag H. Hanssen works as an Assistant Professor in automation at the Institute of Engineering and Safety at the University of Tromsø. During the course of his 18 year long career with the university he has taught many different courses, but he now focusses on control technique, process automation and Application Development.

• Preface xivPart One Hardware 11 About PLCs 31.1 History 41.1.1 More Recent Developments 61.2 Structure 71.2.1 Inputs and Outputs 101.3 PLC Operation 131.3.1 Process Knowledge 141.3.2 Standard Operations 161.3.3 Cyclic, Freewheeling, or Event‐Controlled Execution 181.4 Test Problems 192 Digital Signals and Digital Inputs and Outputs 202.1 Introduction 202.2 Terminology 212.2.1 Discrete, Digital, Logical, and Binary 212.2.2 Sensors, Transducers, and Transmitters 222.3 Switches 242.3.1 Limit Switches 242.3.2 Safety Devices 242.3.3 Magnetic Switches 252.4 Logical Sensors 262.4.1 Inductive Sensors 272.4.2 Capacitive Sensors 292.4.3 Photocells 302.4.4 Ultrasonic Sensors 332.4.5 Rotating Sensors (Encoders) 342.4.6 Other Detection Principles and Sensors 372.5 Connection of Logical Sensors 392.5.1 Sink/Source 412.5.2 Selecting a Sensor with the Proper Type of Output 432.6 Properties of Discrete Inputs 442.7 Discrete Actuators 452.7.1 Relays and Contactors 462.7.2 Solenoids and Magnetic Valves 472.7.3 Transistor Outputs versus Relay Outputs 492.8 Test Problems 503 Analog Signals and Analog I/O 523.1 Introduction 523.2 Digitalization of Analog Signals 533.2.1 Filtering 533.2.2 A/D Conversion 553.3 Analog Instrumentation 583.3.1 About Sensors 583.3.2 Standard Signal Formats 593.3.3 On the 4–20 mA Standard 593.3.4 Some Other Properties of Sensors 613.4 Temperature Sensors 613.4.1 Thermocouple 613.4.2 PT100/NI1000 623.4.3 Thermistors 643.5 Connection 643.5.1 About Noise, Loss, and Cabling 643.5.2 Connecting Sensors 673.5.3 Connection of a PT100 (RTD) 683.5.4 Connecting Thermocouples 723.6 Properties of Analog Input Modules 723.6.1 Measurement Ranges and Digitizing: Resolution 723.6.2 Important Properties and Parameters 743.7 Analog Output Modules and Standard Signal Formats 753.8 Test Problems 76Part Two Methodic 794 Structured Design 814.1 Introduction 814.2 Number Systems 824.2.1 The Decimal Number Systems 824.2.2 The Binary Number System 824.2.3 The Hexadecimal Number System 834.2.4 Binary‐Coded Decimal Numbers 854.2.5 Conversion between Number Systems 864.3 Digital Logic 874.4 Boolean Design 914.4.1 Logical Functional Expressions 914.4.2 Boolean Algebra 934.5 Sequential Design 974.5.1 Flowchart 974.5.2 Example: Flowchart for Mixing Process 994.5.3 Example: Flowchart for an Automated Packaging Line 1014.5.4 Sequence Diagrams 1074.5.5 Example: Sequence Diagram for the Mixing Process 1104.5.6 Example: Batch Process 1124.6 State‐Based Design 1134.6.1 Why Use State Diagrams? 1144.6.2 State Diagrams 1144.6.3 Example: Batch Process 1174.6.4 Example: Level Process 1184.6.5 Example: Packing Facility for Apples 1214.7 Summary 1244.8 Test Problems 125Part Three IEC 61131‐3 1315 Introduction to Programming and IEC 61131‐3 1335.1 Introduction 1335.1.1 Weaknesses in Traditional PLCs 1345.1.2 Improvements with IEC 61131‐3 1365.1.3 On Implementation of the Standard 1375.2 Brief Presentation of the Languages 1385.2.1 ST 1385.2.2 FBD 1385.2.3 LD 1395.2.4 IL 1395.2.5 SFC 1415.3 Program Structure in IEC 61131‐3 1415.3.1 Example of a Configuration 1455.4 Program Processing 1465.4.1 Development of Programming Languages 1465.4.2 From Source Code to Machine Code 1475.5 Test Problems 1516 IEC 61131‐3: Common Language Elements 1526.1 Introduction 1526.2 Identifiers, Keywords, and Comments 1536.2.1 Identifiers 1536.2.2 Keywords 1546.2.3 Comments 1546.3 About Variables and Data Types 1566.4 Pragmas and Literals 1566.4.1 Literal 1576.5 Data Types 1586.5.1 Numerical and Binary Data Types 1586.5.2 Data Types for Time and Duration 1616.5.3 Text Strings 1636.5.4 Generic Data Types 1646.5.5 User‐Defined Data Types 1666.6 Variables 1696.6.1 Conventional Addressing 1706.6.2 Declaration of Variables with IEC 61131‐3 1716.6.3 Local Versus Global Variables 1746.6.4 Input and Output Variables 1756.6.5 Other Variable Types 1766.7 Direct Addressing 1766.7.1 Addressing Structure 1766.7.2 I/O‐Addressing 1786.8 Variable versus I/O‐Addresses 1796.8.1 Unspecified I/O‐Addresses 1796.9 Declaration of Multielement Variables 1806.9.1 Arrays 1816.9.2 Data Structures 1826.10 Test Problems 1847 Functions 1877.1 Introduction 1877.2 On Functions 1887.3 Standard Functions 1897.3.1 Assignment 1907.4 Boolean Operations 1917.5 Arithmetic Functions 1927.5.1 Overflow 1937.6 Comparison 1947.7 Numerical Operations 1957.7.1 Priority of Execution 1967.8 Selection 1977.9 Type Conversion 1977.10 Bit‐String Functions 1997.11 Text‐String Functions 2007.12 Defining New Functions 2027.13 EN/ENO 2037.14 Test Problems 2048 Function Blocks 2068.1 Introduction 2068.1.1 The Standard’s FBs 2078.2 Declaring and Calling FBs 2078.3 FBs for Flank Detection 2088.4 Bistable Elements 2098.5 Timers 2108.6 Counters 2118.6.1 Up‐Counter 2128.6.2 Down‐Counter 2128.6.3 Up/Down‐Counter 2128.7 Defining New FBs 2138.7.1 Encapsulation of Code 2148.7.2 Other Nonstandardized FBs 2168.8 Programs 2178.8.1 Program Calls 2188.8.2 Execution Control 2198.9 Test Problems 220Part Four Programming 2219 Ladder Diagram (LD) 2239.1 Introduction 2239.2 Program Structure 2249.2.1 Contacts and Conditions 2259.2.2 Coils and Actions 2269.2.3 Graphical Elements: An Overview 2279.3 Boolean Operations 2279.3.1 AND/OR‐Conditions 2279.3.2 Set/Reset Coils 2309.3.3 Edge Detecting Contacts 2339.3.4 Example: Control of a Mixing Process 2349.4 Rules for Execution 2379.4.1 One Output: Several Conditions 2379.4.2 The Importance of the Order of Execution 2389.4.3 Labels and Jumps 2399.5 Use of Standard Functions in LD 2409.6 Development and Use of FBs in LD 2429.7 Structured Programming in LD 2449.7.1 Flowchart versus RS‐Based LD Code 2489.7.2 State Diagrams versus RS‐Based LD Code 2539.8 Summary 2599.9 Test Problems 26010 Function Block Diagram (FBD) 26210.1 Introduction 26210.2 Program Structure 26310.2.1 Concepts 26410.3 Execution Order and Loops 26410.3.1 Labels and Jumps 26510.4 User‐Defined Functions and FBs 26610.5 Integer Division 26810.6 Sequential Programming with FBD 27110.7 Test Problems 27311 Structured Text (ST) 27811.1 Introduction 27811.2 ST in General 27911.2.1 Program Structure 28011.3 Standard Functions and Operators 28111.3.1 Assignment 28211.4 Calling FBs 28311.4.1 Flank Detection and Memories 28411.4.2 Timers 28711.4.3 Counters 28811.5 IF Statements 28811.6 CASE Statements 29011.7 ST Code Based upon State Diagrams 29211.7.1 Example: Code for the Level Process 29511.8 Loops 29811.8.1 WHILE … DO… END_WHILE 29811.8.2 FOR … END_FOR 29911.8.3 REPEAT … END_REPEAT 30011.8.4 The EXIT Instruction 30011.9 Example: Defining and Calling Functions 30111.10 Test Problems 30212 Sequential Function Chart (SFC) 30612.1 Introduction 30612.1.1 SFC in General 30712.2 Structure and Graphics 30712.2.1 Overview: Graphic Symbols 30912.2.2 Alternative Branches 30912.2.3 Parallel Branches 31112.3 Steps 31212.3.1 Step Addresses 31312.3.2 SFC in Text Form (for Those Specially Interested…) 31412.4 Transitions 31412.4.1 Alternative Definition of Transitions 31512.5 Actions 31712.5.1 Action Types 31812.5.2 Action Control 31912.5.3 Alternative Declaration and Use of Actions 32112.6 Control of Diagram Execution 32212.7 Good Design Technique 32312.8 Test Problems 32613 Examples 33113.1 Example 1: PID Controller Function Block: Structured Text 33113.2 Example 2: Sampling: SFC 33313.2.1 List of Variables 33413.2.2 Possible Solution 33413.3 Example 3: Product Control: SFC 33713.3.1 Functional Description 33813.3.2 List of Variables 33813.3.3 Possible Solution 33913.4 Example 4: Automatic Feeder: ST/SFC/FBD 34213.4.1 Planning and Structuring 34413.4.2 Alternative 1: SFC 34513.4.3 Alternative 2: ST/FBD 347Part Five Implementation 35114 CODESYS 2.3 35314.1 Introduction 35314.2 Starting the Program 35414.2.1 The Contents of a Project 35614.3 Configuring the (WAGO) PLC 35714.4 Communications with the PLC 36014.4.1 The Gateway Server 36114.4.2 Local Connection via Service Cable 36214.4.3 Via Ethernet 36314.4.4 Communication with a PLC Connected to a Remote PC 36414.4.5 Testing Communications 36514.5 Libraries 36514.6 Defining a POU 36714.7 Programming in FBD/LD 36814.7.1 Declaring Variables 36914.7.2 Programming with FBD 37114.7.3 Programming with LD 37214.8 Configuring Tasks 37514.9 Downloading and Testing Programs 37614.9.1 Debugging 37714.10 Global Variables and Special Data Types 37915 CODESYS Version 3.5 38115.1 Starting a New Project 38115.1.1 Device 38215.1.2 Application 38415.2 Programming and Programming Units (POUs) 38615.2.1 Declaration of Variables 38815.3 Compiling and Running the Project 38915.3.1 Start Gateway Server and PLS and Set Up Communications 39015.4 Test Problems 393Bibliography 395Index 396