Modelling Control Systems Using IEC 61499 (2nd Edition)
2: Atkins, UK
IEC 61499 is a standard for modelling distributed control systems for use in industrial automation, and is already having an impact on the design and implementation of industrial control systems that involve the integration of programmable logic controllers, intelligent devices and sensors. Modelling Control Systems Using IEC 61499. 2nd Edition provides a concise and yet thorough introduction to the main concepts and models defined in the standard. Topics covered include defining applications, systems, distributing applications on the system's devices, function blocks, structuring applications, service interface function blocks, event function blocks, and examples of industrial applications. This second edition has been significantly updated to reflect the current second release of IEC 61499, including changes in the function block model, its execution, and the newly standardized XML exchange format for model artefacts, and to reflect lessons learned from the author's teaching of IEC 61499 over the last ten years. This book will be of interest to research-led control and process engineers and students working in fields that require complex control systems using networked based distributed control.
Inspec keywords: control systems; IEC standards
Other keywords: industrial automation; control systems modelling; IEC 61499
Subjects: Control technology and theory (production); Standards and calibration; Control systems; General control topics; Management and business
- Book DOI: 10.1049/PBCE095E
- Chapter DOI: 10.1049/PBCE095E
- ISBN: 9781849197601
- e-ISBN: 9781849197618
- Page count: 245
- Format: PDF
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Front Matter
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1 Introduction
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This introductory chapter reviews the background and reasons behind the development of the IEC 61499 standard. Specifically the chapter: reviews the design of current day control systems and considers the impact of new technology; looks at the reasons for starting the development of the IEC 61499 standard; considers the reasons why function blocks are still an important concept to process and system engineers; shows how function blocks have some of the characteristics of object- and component-oriented software; and shows 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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This chapter reviews the main models and concepts defined in IEC 61499 to gain a general overview of the function block standard. It is advisable to have some understanding of the material in this chapter before proceeding into any of the following chapters where specific features of IEC 61499 are reviewed in more detail. Topics covered in this chapter include: characteristics of function blocks and their execution; the different forms of function blocks; service interface function blocks to provide interfaces into hardware and operating systems; models to represent applications independent from the system configuration; the system, device and resource models for distributed control systems; the distribution model which assigns applications to the devices and resources; and exchange and storage formats for IEC 61499 entities.
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3 Defining function block types
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This chapter reviews how to create type definitions for function blocks and shows how these can be used to create function block instances. Specifically the chapter: reviews different forms of function block definitions; shows how event and data interfaces can be defined and how the external visible behaviour of function blocks can be described; examines how algorithms are constructed and linked to the event execution; considers how instances of function blocks behave; and shows how function block instances can be aggregated to composite function blocks.
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4 Structuring applications
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This chapter reviews how applications can be hierarchically structured into independent sub-systems using sub-applications and shows how the interaction of function blocks can be decoupled by applying the adapter concept. Specifically the chapter: reviews where sub-applications can be used and compares their behaviour and properties with those of composite function blocks; describes the distribution capabilities of sub-applications; considers how the use of sub-applications can support either a top-down and bottom-up approach to application design; decouples application parts and function blocks using common interfaces defined by adapters; and shows how adapters can be defined and used in applications and in the different function block types.
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5 Service interface function blocks
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This chapter reviews a special form of function block that provides interfaces into the underlying resource and communications systems. Specifically we will: discuss why service interface function blocks are required and show where they can be used; review standard input and output data and event points required in service interface function block type definitions; review how service sequence diagrams are used to describe the behaviour of service interface function blocks; consider some examples of service interface function blocks and look at where they could be applied; describe the two communication models defined in the standard and review the corresponding communication service interface function blocks; finally we will review management function blocks, which are a further specialised form of service interface function block for controlling the creation and management of function blocks within resources and devices.
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6 Event function blocks
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As discussed in Chapters 1 and 2, a fundamental property of IEC 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 describes 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; create events from Boolean edge detection; and count the number of event occurrences.
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7 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 function block model for a conveyor belt control system; consider issues related to modelling systems running on Fieldbus devices; and explore some of the special requirements for function blocks used in process control.
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8 Epilogue
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In this final chapter, we will review how 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; IEC 61499 Part 2 that covers 'Engineering Task Support'; and compliance with IEC 61499 as defined in IEC 61499 Part 4.
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Appendix A: Common elements
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The article outlines the common elements used in IEC 61499 that are based on definitions from the IEC 61131-3 PLC Software Standard. It 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: IEC 61499 Compliance Profile for Feasibility Demonstrations
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The article outlines as an example an IEC 61499 compliance profile, designated: the 'IEC 61499 Compliance Profile for Feasibility Demonstrations'. Currently, most IEC 61499 implementations comply at least in part to this compliance profile. Originally, the profile was developed within the 'Holonic Manufacturing Systems' project to show the inter-vendor feasibility of IEC 61499. The original version was defined by the companies Rockwell Automation, Softing AG and Profactor GmbH. Currently it is hosted and maintained by the company Holobloc Inc. Note: Compliance profiles are typically developed and maintained by organisations not under direct control of the IEC. The scope of this compliance profile is to provide reference definitions for all three aspects (i.e. portability, interoperability and configurability) of IEC 61499 compliance profiles. How these three aspects are defined in the 'IEC 61499 Compliance Profile for Feasibility Demonstrations' is outlined in the article.
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Appendix C: Frequently asked questions (IEC 61499 FAQ)
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The article 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 for IEC 61499 (at that time IEC TC65/WG6). The authors have restructured and added additional comments to some of the answers. Furthermore the authors have updated the comments to be consistent with the current version of the IEC 61499 standard and also provided some additional questions with answers.
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Appendix D: PID function block example
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The article depicts how a proportional, integral and derivative (PID) algorithm can be encapsulated as a composite function block. 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. Examples are: to control the temperature of a heat treatment oven where the internal temperature has to remain stable while the oven door is opened and different loads are inserted into the oven, or to control the pressure in a reactor vessel while a chemical reaction is progressing. The PID algorithm uses the error between the current Process Value (PV) and the desired process value or Set-Point (SP), along with the integral and derivative values of the error, to calculate a new output value to drive the process. This output value is used to drive an actuator to, say, adjust the current in a heater or change a pump speed in order to bring the process value closer to the SP. A PID algorithm has a number of parameters that must be 'tuned' to match the process under control. This is required to ensure that the control action is responsive and has minimum overshoot. An application using a PID is discussed. The main features of the PID algorithm are shown. This example is intended to demonstrate the use of IEC 61499 to encapsulate algorithms.
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Appendix E: Exchange formats
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The article gives a brief overview of the main keywords and structure used in the IEC 61499 Textual Syntax and XML format. It is provided to assist with the understanding of the examples of Textual Syntax and XML format given in the book. For a full description and the full and formal production rules of the Textual Syntax, the reader is advised to read Annex B of IEC 61499-1. For a full description of the XML format and the associated Document Type Definition, the reader is advised to read Annex A of IEC 61499-2.
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Appendix F: Bibliography
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Back Matter
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