1 January 2007
Ethernet wise to the enterprise
A blurring of the traditional boundaries between operation execution and business logistics is occurring
By Jonas Berge
Traditionally, the automation system has been an isolated island—not connected to anything. However, new methods of operation require remote access for visualization and supervision of the controls through a live link. This requires network access to the automation system from other parts of the enterprise.
Up-to-date data from the automation system is required for activities and decision support at the execution and business levels. Therefore, the automation needs connectivity to the upper levels.
The control-level network, therefore, has to connect to the operations information network and the business logistics network.
Since it is paramount to protect the integrity of the automation system, a firewall should lodge between the automation system and any other networks.
For administrative reasons, it is better to use two firewalls back-to-back. This way the responsibility for the automation-side firewall can rest with the automation systems engineers, while the responsibility for the IT-side firewall rests with the IT network administrators. This leaves a clear demarcation line for the responsibilities.
Since packet-filtering firewall is between the automation system and the rest of the enterprise, it is necessary to use Web technologies to bring the data across the networks.
Moreover, automation networking protocols and software interfaces such as OPC do not work with common IT applications and business software. Therefore, standard IT technologies for the Web are ideal for integration with higher levels of the enterprise.
Execution systems cross the information boundary between automation and business systems. One of the functions of the software at the border between the automation level and the execution level is to take OPC data and present it in a Web-based format.
Today the network technology used at all three levels is the same—IP on Ethernet. The systems and applications are technically on the same network, albeit usually on separate IP subnets. The result is homogenous network architecture.
Because inserting firewalls between the automation network and the information network creates the need for additional hardware and software to support Web technologies, it is tempting not to use a firewall. However, the firewall and other security equipment are necessary to protect the control network from problems originating from the execution and business levels.
Make the legacy system coexist
Since the network infrastructure technology at the different levels is now the same, and the applications are modular rather than monolithic, it is very hard to draw a distinct line between automation software and execution software.
For example, the SQL server database, now often found as an integral part of the automation systems' operator visualization software, has traditionally been the core of MES software or so the perception goes.
In the past, the automation system such as a DCS did not have the database capacity for long-term trends; it left that to the separate historian applications part of the execution system, which had a completely independent database.
Today, an SQL server often serves as the interface between automation and execution.
The automation application is now populating the shared historian server "data warehouse" with data, with the execution software clients consuming it.
The applications in business systems are transaction-based, using the SQL database as the interface rather than interfacing direct application-to-application.
The automation and execution applications are merging into a single "control domain" below the enterprise domain. A similar blurring of the traditional boundaries between operation execution and business logistics is also occurring.
Throughout the three levels, TCP/IP on Ethernet is the network platform of choice. Simply connecting a business system to the automation system would overload the business system and network with data.
Software at the execution level extracts and distills automation system data to the information required for decision support at the business level. This typically means reports of integrated totals, summary charts, as well as easy to grasp Key Performance Indicators, or KPI, numbers.
Existing automation systems 10+ years old found in plants, buildings, and on production lines are not based on open technologies and do not have connectivity required to integrate with the execution and business levels to reap subsequent benefits.
Therefore, to achieve a totally integrated system, a plan for change needs to be in place. The long-term objective is usually to replace the entire legacy DCS or PLC to benefit from lower-level fieldbus networking, but short-term this is often not feasible. Therefore, the first step is to make the legacy system coexist with the newer systems. Such integration usually entails replacing workstations and software of the existing automation system with modern applications, based on OPC.
Be aware, having the automation system connected, particularly permanently, to the enterprise LAN and outside world has security issues.
At the lower-end, a modern automation system integrates with sensor and actuator hardware networked using fieldbus technology. At the upper-end, the automation system integrates with execution software applications that, in turn, integrate with business software applications.
An MES proactively manages manufacturing processes, and an ERP system proactively manages business processes. This is where automation software meets regular IT.
While the automation system handles visualization and control, the MES does track and trace, performance analysis, maintenance, and document management.
The ERP, in turn, handles finance, order management, and logistics.
The need for enterprise integration is very much the result of e-business. In an e-business scenario, the initial delivery time promise requires knowledge of machinery and processing equipment availability as well as raw material inventory.
This information for decision support must come from diagnostics and measurements ultimately originating from the shop floor. Orders from customers must find their way into the production planning, individual product items down to detail production scheduling, and, lastly, as the required machine and equipment settings.
Once in production, fulfillment progress updates, quality reports, and the like pushed to the customer originate from information percolated up from field measurements.
Throughout this process, the production, quality, and maintenance departments need their specific information. For example, there are many bidirectional transactions between the layers, and a fully automated solution requires integration between the systems at all levels.
The connectivity characteristics are very different at the different levels of the plant hierarchy. At the lower-end, network protocols such as Foundation fieldbus have very tight interoperability including strong data typing and definition of semantics for the data.
At the automation level, OPC provides relatively tight connectivity but do not cover semantics and provide great flexibility for data types, thus requiring some configuration and possibly scripting for interpreting the data.
Between applications at the MES and ERP levels, the integration is loose, generally requiring special data mapping applications or even drivers in order to patch data from sources to consumers together.
Lose coupling means more work for the system integrator, and thus higher costs for the end user.
For many proprietary systems at automation, execution, and business levels, integration is not possible at all, since database formats and application interfaces are unseen.
Traditional systems for automation, execution, and business are usually monolithic, having proprietary interfaces between inseparable applications.
The trend at the execution and business levels is now towards open interfaces and applications using Web technologies.
All applications at the execution level are very much about consolidating information from various sources, compiling the data into reports, and summarizing them into key performance indexes. Therefore, it is important that all underlying data sources have open interfaces based on specifications, such as OPC, to provide easy access to the data.
Some also support ActiveX, making it possible to include information in other displays. Similarly, MES applications must have open interfaces to exchange data among themselves and to make it available to higher-level business applications.
Huge amounts of data for all
Traditionally, the automation system and execution system have separate databases. It is still common that the plant-information-management system is a stand-alone application that interfaces to the automation system through a driver or OPC.
However, it is increasingly common that a powerful SQL based plant information database performing trend and alarm & event logging is part of the automation system. At the execution level, the primary function is increasingly to provide a "portal" to publish consolidated information and summaries.
At the execution and business levels, the interfaces between applications are not well defined and interchanges are occasional, across firewalls and domains, and even between different operating systems.
At these levels, exchange platforms on message transactions between loosely coupled applications. Therefore, Web services and the Microsoft .NET framework are more suitable than DCOM.
Applications at this level store and process huge amounts of data for very many users. The .NET framework is scalable to multiprocessing platforms and therefore better handles large loads.
ABOUT THE AUTHOR
Jonas Berge (Jonas.Berge@AP.EmersonProcess.com) is a senior member of ISA and president of the Fieldbus Foundation Marketing Society in Singapore. He is the author of the books Fieldbuses for process control: Engineering, Operation, and Maintenance and Software for Automation: Architecture, Integration, and Security. He received the 1999 ISA award for excellence in documentation.
OPC data access is a group of standards and specifications for communicating real-time data from data acquisition devices such as programmable logic controllers (PLCs) to display and interface devices like human-machine interfaces (HMI). The specifications focus on the continuous communication of data.
TCP/IP: Transmission Control Protocol/Internet Protocol is the suite of communications protocols used to connect hosts on the Internet and local area networks (LAN).
MES: Manufacturing execution systems use network computing to automate production control and process. By downloading "recipes" and work schedules and uploading production results, MES bridge the gap between business and plant-floor or process-control systems.
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