AUTOMATION SYSTEM ARCHITECTURE USING OPEN INDUSTRIAL STANDARDS
WILLIAM D. FERRAZ, RODRIGO P. PANTONI
Smar Equipamentos Industriais Ltda. Av Antonio Furlan Jr. 1622 CEP 14160500 Sertaozinho - SP E-mails: [email protected] , [email protected]
Abstract In modern industries the control systems are inserted inside a broader context other then the control problem do- main. This broader context is generally referred to as Automation System, which also addresses peripheral issues like control data management and associated communication protocols, maintenance of the control system components (e.g. sensors and fi- nal control elements) known as ‘Asset Management’, management of data exchange among subsystems, interoperability among devices and among systems, etc. This article shows that most of the previous mentioned issues are addressed using not only elec- tronics and network standards as well as open industrial software standards in the host level (control room workstations) estab- lished upon a common open architecture for automation systems based on SOA (Service Oriented Architecture).
Keywords Industrial Standards, SOA, Network of things, Automation System Architecture
1- Introduction requirements like quality and reliability, stability and safety issues among others, it is necessary to have In modern industries the control systems are in- data and information flowing up and down through serted inside a broader context other then the control the several different layers that compose an enterprise problem domain. This broader context is generally structure, and thus through distinct information- referred to as Automation System, which also ad- domains e.g. Neural-Network and PID control (elec- dresses peripheral issues like control data manage- tronics engineering domain) affecting production ment and associated communication protocols, main- efficiency and planning (Production Management tenance of the control system components (e.g. sen- domain). The automation systems community soon sors and final control elements) known as ‘Asset realized that it is not effective, and in some cases Management’, management of data exchange among even not acceptable, to try to siege technology as subsystems, interoperability among devices and well as knowledge development and usage by using among systems, etc. This article shows that most of proprietary solutions or proprietary artifacts. This the previous mentioned issues are addressed using context conducted the development of non- not only electronics and network standards as well as proprietary solutions. To harmonize different ven- open industrial software standards in the host level dors' solutions (non-proprietary) for distinct informa- (control room workstations). Thus, the automation tion domains accomplishing the engineering require- systems evolved in the last decade from stand-alone ments, it is common sense that the enterprise automa- specialized workstations using vendor-specific (pro- tion system might rely upon a common architecture prietary) standards for hardware, software and com- (Emerson, 2005) (Gelle et al, 2003) to enable open munication protocols to full-fledged hardware and standards interoperability. software architecture supporting high-speed data ex- In order to mitigate what have been exposed change among all sorts of entities, from biometrics above, international non-profit organizations play a and Internet-aware components to valve positioners fundamental role. Some of them, like OPC Founda- (Peluso and Wallace, 2003). This augmentation in the tion (OPC – OLE for Process Control), Fieldbus amount of digital-communication enabled devices FoundationTM (FF) and IEC (International Electro- and the associated data processing generated by the technical Commission) cooperate among themselves interaction of these devices requires not only the to enable the development of open and consistent state-of-the-art on software and hardware develop- automation system architectures. Examples of such ment but it requires the knowledge of the state-of-the- efforts are the FF HSE (High Speed Ethernet) speci- art technology to design the system architecture to fications, IEC 61804-2 (EDDL - Electronic Device handle the communication involved in such architec- Description Language) and OPC UA (Unified Archi- ture. Dominance over such technologies that can tecture) specifications (Fieldbus Foundation, 1999a properly deal with the huge amount of information and 199b) (OPC Foundation, 2006). available in the nowadays automation systems net- As it's demonstrated in the next paragraphs, an work is necessary to transform raw information in automation system that combine the implementation usable knowledge (Hayes and Alberts, 1996) and also of such technologies is able to succeed in the hard to control the information exchange (Duchastel, task of observe, classify and use information to cope 2001) between the network components. with the enterprise ROI (Return Of Investment) and In order to guarantee the accomplishment of TCO (Total Cost Of Ownership). common factory-floor production and engineering
63 of 67 by FF, has no counterpart in other open specification 2- FF HSE – Open Specifications to such as MODBUS. Implement a Common Network Architecture for Interoperability
Obviously, the Enterprise production infra- structure is the basic source of the Automation Sys- tem's raw data. In the modern plants, however, the data generated varies from simple measurements like a pressure value to complex diagnostics information like a valve signature1 or even measurement subsys- tems. Analog technologies are not suitable to transmit this amount of data, so the technology evolved to- wards digital-processor field devices in the last two Figure 1: FF HSE Architecture decades. However, technologies and standards appear and The FF systems' architecture is composed of disappear all the time. Often, those who buy into the two parts. The (low-speed) factory-floor part, named 'technology de jour'2 have later been disappointed ‘H1’ and the systems' backbone communication net- and incurred in unnecessary expense to replace a work named ‘HSE’, taking the acronym from the 'promising' but unsupported technology. Ethernet's definition High Speed Ethernet, since the Therefore, when discussing digital field automa- communication relies upon the well known and ac- tion technology architectures, users state their con- cepted Ethernet standard. cerns a hundred different ways, but in the end, what users (Business and Process) seek are assurances the 3- EDDL – The Experts Talk technology platform they choose provides (Zielinski, 2004): FF HSE User layer uses the Electronic De- • Freedom of choice in plant floor instrumen- vice Description Language (EDDL) to describe the tation and equipment independent of the devices throughout the FF-HSE-based system. EDDL Host - valves, transmitters, motor starters, is a text-based language for describing the digital remote IO, etc.; communication characteristics of intelligent field • Consistency in how plant floor instrumenta- instrumentation and equipment parameters—device tion and equipment is engineered; status, diagnostic data, and configuration details—in • Flexibility and efficiency in how plant-floor an operating system and Human Machine Interface data are shared throughout the enterprise; (HMI) neutral environment. • Ease of maintenance; Everyone is aware of the difficulties of get- • Quantified proof that adopting manufactur- ting device software drivers to work after a host plat- ers have long-term commitments to expand form OS upgrade. EDDL was specifically designed and improve the underlying technology; for the EDD (Electronic Device Description) file to • Easy access to production data; avoid this issue. The IEC 61804-2 standard is not • Easy connectivity throughout the business only OS (Operational System) and HMI independent, endpoint; but also fieldbus communication protocol neutral. • Enough resources for data mining. Today EDDL technologies establishes the engineering and operating base on which all major Among several solutions, the non-profit organi- digital fieldbus protocols—FOUNDATION Field- zation Fieldbus FOUNDATIONTM presented an ap- bus™, HART®, and PROFIBUS—construct para- proach that meets the requirements of the modern metric and device descriptions. And, because EDDL enterprise's infrastructure network mentioned above. is an open technology with international standard As shown in the figure 1, the FF HSE system archi- status, it can be easily and effectively applied to any tecture provides a framework for describing the device and any fieldbus protocol (Emerson , 2005). automation system as a collection of physical devices From an end-user perspective, it's equally interconnected by a fieldbus network (Fieldbus reassuring to know that a host workstation change Foundation, 1999a). from any OS to any other without require modifica- The FF's architecture is comprised of a con- tion of the existing EDD files. It is possible to men- sistent hardware and software architecture envisaging tion two typical examples like: migration of the host an optimum integration with the end-user, through a platform (OS) from Windows NT to Windows 2003 layer called ‘User-Layer’, which, in the extent given Server or from Windows to Linux. Allying the FF HSE architecture and EDDL capability is possible to integrate not only the com- 1 Valve signature plots actuator pressure versus travel munication systems between networks but it's possi- (actuator stem position variation over time) ble to integrate the device manufacturer know-how to 2 French expression. Technology-of-the-day, not proven- in-use technology the automation infrastructure. However, the automa-
64 of 67 tion system vendor is not limited to the device manu- cation among different software of different plat- facturer know-how. It can also join its own knowl- forms, providing interoperability (state of the art in edge to it. IT) (OPC Foundation, 2006). In February 2003, representatives of, FF, The Extensible Markup Language (XML) is HCF (HART Communication Foundation) and PNO a non-proprietary specification for document inter- (PROFIBUS NutzerOrganisation) met in a collabora- change in the Internet that the World Wide Web tive project to extend the capabilities of the IEC Consortium (W3C) developed in 1998 (Roy and Ra- 618342 standard. manujan, 2000). XML lets interoperability of differ- The scope of the co-operative project is to ent software of different platforms to transfer infor- add robust organization and graphical visualization mation using a common language. Since XML is a of device data as well as support for persistent data meta-language, it is possible to create new languages storage (i.e., permanent data storage) features to IEC to make a standard talk. In Mathematics for example, 61804-2. Sophisticated devices. As it is protocol and a XML based language called MathML is in use in technology independent (different from other tech- the same way OPC uses SOAP (Gelle et al, 2003). nologies with the same purpose like FDT - Field De- The OPC Foundation has joined the interna- vice Tool (Merrit, 2002)), it is even more efficient tional cooperative team of the three leading fieldbus when using FF-HSE, with its user-layer, to empower organizations, the Fieldbus FoundationTM (FF), data and information transfer. HART Communication Foundation (HCF), and PROFIBUS NutzerOrganisation e.V. (PNO), to ex- 4- OPC AND OPC-UA tend the reach of electronic device descriptions (EDDs) into the OPC unified architecture. This work The rising of OPC technology made the provides the total integration between OPC UA and HMI software manufacturers have to develop only a EDDL to describe data to the host reads, i.e., OPC driver for communication with devices, differently of Clients have access to complex device data with the way before, which each manufacturer had to de- automatic integration. This lets an easier and cheaper velop proprietary drivers for supporting its devices. development, which brings a better quality for the A common analogy for OPC DA (Data Ac- product to the final user (Fieldbus Foundation, 2006). cess) is printer drivers in DOS versus Windows. In Thus, OPC UA is the key to improve the DOS, the application developer had to write a printer transformation of simple data in knowledge, due to driver for every printer. So AutoCAD, WordPerfect, the open high-level mechanism, open the doors to and Netscape all had to write a separate printer driver store the information by an easer way for MES for every printer they wanted to support. In industrial (Manufacturing Execution System) and ERP (Enter- automation, companies like Rockwell Automation, prise Resource Planning) applications. ICONICS and Citect wrote their own HMI software and a proprietary driver for each industrial device 5- COMMON OPEN ARCHITECTURE AND including every PLC (Programmable Logic Control- XML ler) brand in order to retrieve process data. The standardization of these drivers was de- Although the above-mentioned technologies veloped by a group of manufactures that have im- can enable the development of an efficient yet inter- proved the OPC model due to them additions based operable automation system in order to establish a on past experiences. It is mentioned for example the common architecture, other features are necessary. navigation system of the OPC tags through tree struc- These other requirements are necessary because FF- ture, and its division by sectors. HSE, EDDL and OPC do not provide resources, for Since 2003, OPC Foundation and a group of instance, to implement binary and sequential logic as IHM and device manufactures have been working in well as enterprise representation (which are better a joint venture to define and implement a new OPC provided by the IEC 61131 standard and ISA S-88). Specification. This new Specification is the OPC UA. Then it is very clear that another technology The purpose of OPC UA is to provide en- is necessary to integrate all the different standards hancements for existing and next generation OPC used in the automation system. As can be inferred products in the areas of security, reliability, and in- from the previous sections, the best approach to pro- teroperability. OPC UA is designed to unify existing mote integration of data, communication and even OPC specifications such as DA, DX (Data Ex- graphical elements is the usage of XML (W3C, 2006) change), HAD (Historical Data Access), and XML (and its variations like XML Schema, XSLT - eXten- (eXtensible Markup Language) DA into an environ- sible Stylesheet Language Transformations, etc). ment that will leverage Web-based technologies and XML is used to integrate different software layers as standards such as Web Services, WSDL (Web Ser- well as the software in the same network layer be- vices Description Language), XML and SOAP (Sim- cause it is also open (in fact it is public), platform ple Object Access Protocol). independent and has a great number of programs and The OPC UA is based on SOA (Service APIs that allow easy manipulation (read and write Oriented Architecture) through Web Service that operations) of XML files. Even other specifications transports XML data, which provides the communi- are being produced having XML as basic element of
65 of 67 information and data description, like SOAP, SAX (Simple API for XML), DOM (Document Object Model) and SVG (Scalable Vector Graphics ) (Tan- taleán, 2003) (Gelle et al, 2003). Thus, XML can directly consolidate not only device internal data (described, for instance, by EDDL, CFF - Capability File Format and CFH - Ca- pability File for FOUNDATION FieldbusTM HSE) but also its relationship with the communication workspace (FF, OPC and CORBA - Common Object Figure 3: The ‘Network of Things’ Request Broker Architeture) as well as configuration and visualization tools (IEC61131, ISA-S88, SGML, SVG). Having XML as the common language being According to ARC (The ARC Strategies used by the different components of the system, it is Report, 2001), one set of the benefits is shown in the possible to extend the cognition to the upper layers of following graph (Figure 4), which guarantee better the automation system facilitating the integration of ROI figures than conventional, proprietary systems the system with business endpoints, MES, etc. The (Verhappen, 2005). figure 2 represents the SOAP / XML as the integra- tion technology.
Figure 4: Benefits of a common open architecture Source: ARC Figure 2: SOAP-XML as the core ‘language’ of the Common Automation Architecture This graph (Figure 4) reflects how import is to choose not only the best control strategy (or algo- The adoption of such Automation System rithms) but also the components and associated soft- Architecture, can assure long-term integration of the ware used to implement the control system itself and Manufacturing Facility with other business endpoints, its insertion in the enterprise automation. This means since SOAP-XML is currently being applied in all that the gains obtained by using a better control sys- sorts of business automation structures. tem algorithm will not be evident if a sensor used in the implementation is affected by defects not quickly 6- CONCLUSIONS detected. Using modern software the resolution of such defects could be done faster than using legacy The nowadays technology is presenting a software and equipment, reducing the downtime and new challenge to the mankind, which is the ability to consequently, reducing unplanned breakdown. construct networks of virtually anything. Some has To fully accomplish the above-mentioned called this as ‘network of things’ (Sang, 2006). This scenario this article has shown that the Automation new reality, as shown in figure 3, will need not only System of the Total Information Age should be able new network approaches but also solutions to deal to map the intricacies of its problem domain into with such amount of information exchanged through- SOAP/XML using open standards, constructing a out the network. The new ‘network of things’ sce- common open architecture. It was shown that EDDL, nario will be constructed on devices that have an en- FF-HSE and OPC UA are able to accomplish such hanced cognition ability, using SOAP /Web Services, task. TCO is then mitigated since this approach will characterizing the ‘Total Information Age’. prepare the enterprise to face the nowadays needs and The first implementations of systems that also the future fractal network structure, where the are using these technologies have demonstrated sev- users will have almost no concern about the network eral benefits not only for technicians but also for en- and software technology being used but they will be terprise managers and business agents. concerned about the services being offered.
66 of 67 GLOSSARY Fieldbus Foundation (2006).
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Duchastel, P.(2001). Towards an information realm. Digit.hvm. ISSN 1575-2275.
Emerson (2005). White paper: EDDL Technology.
Fieldbus Foundation (1999a). FF-581-1.3: System Architecture.
Fieldbus Foundation (1999b). FD-043-2.0: Technical Overview.
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