PROGRAMMABLE LOGIC CONTROLLERS. Wiley USING CODESYS A PRACTICAL APPROACH TO IEC. Dag H. Hanssen Institute of Engineering and Safety,

Transcription

1 PROGRAMMABLE LOGIC CONTROLLERS A PRACTICAL APPROACH TO IEC USING CODESYS Dag H. Hanssen Institute of Engineering and Safety, University oftroms0, Norway Translated by Dan Lufkin Wiley

2 Contents Preface xiv PART ONE HARDWARE 1 1 About PLCs History More Recent Developments Structure Inputs and Outputs PLC Operation Process Knowledge Standard Operations Cyclic, Freewheeling, or Event-Controlled Execution Test Problems 19 2 Digital Signals and Digital Inputs and Outputs Introduction Terminology Discrete, Digital, Logical, and Binary Sensors, Transducers, and Transmitters Switches Limit Switches Safety Devices Magnetic Switches Logical Sensors Inductive Sensors Capacitive Sensors Photocells 30

3 vi Contents Ultrasonic Sensors Rotating Sensors (Encoders) Other Detection Principles and Sensors Connection of Logical Sensors Sink/Source Selecting a Sensor with the Proper Type of Output Properties of Discrete Inputs Discrete Actuators Relays and Contactors Solenoids and Magnetic Valves Transistor Outputs versus Relay Outputs Test Problems 50 3 Analog Signals and Analog I/O Introduction Digitalization of Analog Signals Filtering A/D Conversion Analog Instrumentation About Sensors Standard Signal Formats On the 4-20mA Standard Some Other Properties of Sensors Temperature Sensors Thermocouple PT100/NI Thermistors Connection About Noise, Loss, and Cabling Connecting Sensors Connection of a PT100 (RTD) Connecting Thermocouples Properties of Analog Input Modules Measurement Ranges and Digitizing: Resolution Important Properties and Parameters Analog Output Modules and Standard Signal Formats Test Problems 76 PART TWO METHODIC 79 4 Structured Design Introduction Number Systems The Decimal Number Systems The Binary Number System 82

4 Contents The Hexadecimal Number System Binary-Coded Decimal Numbers Conversion between Number Systems Digital Logic Boolean Design Logical Functional Expressions Boolean Algebra Sequential Design Flowchart Example: Flowchart for Mixing Process Example: Flowchart for an Automated Packaging Line Sequence Diagrams Example: Sequence Diagram for the Mixing Process Example: Batch Process State-Based Design Why Use State Diagrams? State Diagrams Example: Batch Process Example: Level Process Example: Packing Facility for Apples Summary Test Problems 125 PART THREE IEC Introduction to Programming and IEC Introduction Weaknesses in Traditional PLCs Improvements with IEC On Implementation of the Standard Brief Presentation of the Languages ST FBD LD IL SFC Program Structure in IEC Example of a Configuration Program Processing Development of Programming Languages From Source Code to Machine Code Test Problems IEC : Common Language Elements Introduction 152

5 viii Contents 6.2 Identifiers, Keywords, and Comments Identifiers Keywords Comments About Variables and Data Types Pragmas and Literals Literal Data Types Numerical and Binary Data Types Data Types for Time and Duration Text Strings Generic Data Types User-Defined Data Types Variables Conventional Addressing Declaration ofvariables with IEC Local Versus Global Variables Input and Output Variables Other Variable Types Direct Addressing Addressing Structure I/O-Addressing Variable versus I/O-Addresses Unspecified I/O-Addresses Declaration of Multielement Variables Arrays Data Structures Test Problems Functions Introduction On Functions Standard Functions Assignment Boolean Operations Arithmetic Functions Overflow Comparison Numerical Operations Priority of Execution Selection Type Conversion Bit-String Functions Text-String Functions Defining New Functions EN/ENO Test Problems 204

6 Contents 8 Function Blocks Introduction The Standard's FBs Declaring and Calling FBs FBs for Flank Detection Bistable Elements Timers Counters Up-Counter Down-Counter Up/Down-Counter Defining New FBs Encapsulation of Code Other Nonstandardized FBs Programs Program Calls Execution Control Test Problems 220 PART FOUR PROGRAMMING Ladder Diagram (LD) Introduction Program Structure Contacts and Conditions Coils and Actions Graphical Elements: An Overview Boolean Operations AND/OR-Conditions Set/Reset Coils Edge Detecting Contacts Example: Control of a Mixing Process Rules for Execution One Output: Several Conditions The Importance of the Order of Execution Labels and Jumps Use of Standard Functions in LD Development and Use of FBs in LD Structured Programming in LD Flowchart versus RS-Based LD Code State Diagrams versus RS-Based LD Code Summary Test Problems Function Block Diagram (FBD) Introduction 262

7 END_FOR DO... END_REPEAT X Contents 10.2 Program Structure Concepts Execution Order and Loops Labels and Jumps User-Defined Functions and FBs Integer Division Sequential Programming with FBD Test Problems Structured Text (ST) Introduction ST in General Program Structure Standard Functions and Operators Assignment Calling FBs Flank Detection and Memories Timers Counters IF Statements CASE Statements ST Code Based upon State Diagrams Example: Code for the Level Process Loops WHILE... ENDJWHILE FOR REPEAT The EXIT Instruction Example: Defining and Calling Functions Test Problems Sequential Function Chart (SFC) Introduction SFC in General Structure and Graphics Overview: Graphic Symbols Alternative Branches Parallel Branches Steps Step Addresses SFC in Text Form (for Those Specially Interested...) Transitions Alternative Definition of Transitions Actions Action Types Action Control Alternative Declaration and Use of Actions 321

8 Contents xi 12.6 Control of Diagram Execution Good Design Technique Test Problems Examples Example 1: PID Controller Function Block: Structured Text Example 2: Sampling: SFC List of Variables Possible Solution Example 3: Product Control: SFC Functional Description List of Variables Possible Solution Example 4: Automatic Feeder: ST/SFC/FBD Planning and Structuring Alternative 1: SFC Alternative 2: ST/FBD 347 PART FIVE IMPLEMENTATION CODESYS Introduction Starting the Program The Contents of a Project Configuring the (WAGO) PLC Communications with the PLC The Gateway Server Local Connection via Service Cable Via Ethernet Communication with a PLC Connected to a Remote PC Testing Communications Libraries Defining 14.7 Programming in FBD/LD 368 a POU Declaring Variables Programming with FBD 371 with LD Programming 14.8 Configuring Tasks Downloading and Testing Programs Debugging Global Variables and Special Data Types CODESYS Version Starting a New Project Device Application 384

9 xii Contents 15.2 Programming and Programming Units (POUs) Declaration of Variables Compiling and Running the Project Start Gateway Server and PLS and Set Up Communications Test Problems 393 Bibliography 395 Index 396