Modelling Control Systems Using IEC 61499. Applying function blocks to distributed systems
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New technologies and standards are emerging which will have a dramatic effect on the design and implementation of future industrial control systems. This book provides a concise yet thorough introduction to the main concepts and models defined in the IEC 61499 standard and particularly the use of function blocks.
Inspec keywords: distributed control; industrial control; IEC standards
Other keywords: distributed systems; function blocks; industrial problems; IEC 61499 standard; functionality; distributed control systems
Subjects: Control applications; Control technology and theory (production); Control system analysis and synthesis methods; Standards and calibration
- Book DOI: 10.1049/PBCE059E
- Chapter DOI: 10.1049/PBCE059E
- ISBN: 9780852967966
- e-ISBN: 9781849190367
- Page count: 208
- Format: PDF
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Front Matter
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1 Introduction
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In this introductory chapter we review the background and reasons behind the development of the IEC 61499 standard. Specifically we will: review the design of current-day control systems and consider the impact of new technology. Look at the reasons for starting the development of the IEC 61499 standard. Consider the reasons why function blocks are still an important concept to process and system engineers. Show how function blocks have some of the characteristics of object oriented software. And finally show how IEC 61499 models can be used in the control system development life-cycle.
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2 IEC 61499 models and concepts
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We review the main models and concepts defined in IEC 61499 to gain a general overview of the Function Block Standard. Topics covered in this chapter include: the system, device and resource models for distributed control systems; models for representing distributed applications; characteristics of function blocks and their execution; type specifications for different forms of function block; service interface function blocks to provide interfaces into hardware and operating systems; adapters for sharing block interfaces; and textual syntax for defining IEC 61499 entities.
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3 Defining function block and subapplication types
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This chapter reviews how to create type definitions for function blocks and subapplications and show how these can be used to create function block instances and copies of subapplications. Specifically it (1) review different forms of function block definition (2) show how events and data interfaces can be defined (3) examine how algorithms are constructed and linked to the event execution (4) consider how instances of function blocks behave (5) review where subapplications can be used and compare their behaviour and properties with composite function blocks.
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4 Service Interface function blocks
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We have now covered the important features of IEC 61499 Service Interface functions. Service Interface (SI) function blocks are provided to give an interface between function blocks running in the resource and services provided outside the resource. An SI function block type definition only defines the interface into the service and its response; it does not define the service behaviour outside the resource. A special notation, the Time-sequence diagram, is used to show the timing relationships between events on the input and output side of SI bocks.
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5 Event function blocks
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As discussed in chapters 1 and 2, a fundamental property of lEC 61499 function block networks is that the execution of all software within every function block is, in some way, event triggered. In this chapter we will review a special set of standard function blocks that are provided for event behaviour. These function blocks can be used to model the control, generation and detection of events. This chapter will describe the standard event function blocks that: allow events to be split to produce new events; allow events to be merged; permit the propagation of particular events; select between two or more events; delay an event by a given period; generate streams of events; and create events from Boolean edge detection.
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6 Industrial application examples
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In this chapter we will consider how the IEC 61499 concepts and standard function blocks can be applied to modelling some examples of industrial control systems. Specifically we will: model a simple temperature control system and its main function blocks consider how to design a FB model for a conveyor belt control system consider issues related to modelling systems running on Fieldbus devices explore some of the special requirements for function blocks used in process control.
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7 Future development
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In this final chapter we will review how the IEC 61499 standard is likely to develop in the future and its possible impact on the design of systems and support tools. This chapter will review: current limitations of part 1 of the IEC 61499 standard; proposals for IEC 61499 part 2 that covers 'Engineering Task Support' ; requirements of a standard file exchange format for porting; and future developments.
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Appendix A: Common Elements
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This appendix outlines the common elements used in TEC 61499 that are based on definitions from the IEC 61131-3 PLC Software Standard. This appendix is provided as a brief overview -the formal definitions for all of these elements are given in Part 3 of the IEC 61131 standard.
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Appendix B: Overview of XML
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This appendix gives a brief overview of the XML language and the reasons why it has been chosen as a file exchange format for IEC 61499 library elements, for example, for exchanging function block definitions between engineering support systems and other IEC 61499 compliant applications.
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Appendix C: Frequently Asked Questions (IEC 61499 FAQs)
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This appendix is a compendium of frequently asked questions with answers concerning the development and application of the IEC 61499 Function Block Standard. The answers have been provided by international experts working in the IEC working group (IEC 65/WG6) and are not necessarily consistent with the current version of the IEC 61499 standard. The author has restructured and added additional comments to some of the answers and also provided some additional questions with answers.
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Appendix D: PID Function block example
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A PID algorithm is used in 'closed loop' control where there is a requirement to control a process that may be subject to disturbances caused by external factors or by unpredictable changes to the process. In the example discussed in this chapter, the PID function block is constructed by connecting instances of three function blocks: FB_INT, FB_DEV and FB_CALC. These are created from DERIVATIVE_REAL, INTEGRAL_REAL and PID_CALC function block types, respectively. The DERIVATIVE_REAL and INTEGRAL_REAL blocks provide derivative and integration functionality for inputs of REAL data type and are based on definitions given as examples in the IEC 1131-3 PLC software standard. The PID_CALC block encapsulates the PID algorithm and calculates a new output value that is proportional to a weighted summation of the error, the derivative of the error and the integral of the error.
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Appendix E: Textual syntax
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This appendix gives a brief overview of the mainkeywords used in the IEC 61499 Textual Syntax. It is provided to assist with the understanding of the examples of Textual Syntax given in this book. For a full description and the full and formal production rules, the reader is advised to read Annex B in IEC 61499, Part 1. Text enclosed in quotes '...' are keywords, text enclosed in angle brackets <...> is descriptive.
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Back Matter
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