Distributed HMI - Information And Control Where You Need It Most

By adopting a distributed HMI architecture, companies access and contol information from various areas within the enterprise.

If most machines could talk to us—a la Hal in “2001: A Space Odyssey”—there’d be no need to look at interface screens. And, at that point, the machines themselves would probably be self-diagnosing and self-maintaining. But despite the turn of the millennium, humans are still very much a part of the human machine interface (HMI) equation.

That is not to say advances aren’t continually being made. In fact, one of the most important changes to the way information and control are accessed and executed can be found in a distributed HMI architecture. With a distributed architecture, real-time data can be viewed and controlled from near and remote access points. Distributed HMI systems also can be upgraded and maintained more efficiently than stand-alone systems. Finally, distributed HMI can deliver a high level of integration among what had been islands of automation—and connect that shop-floor information to the top-floor systems that need it.

Distributed vs. centralized
The concept of distributed computing, which has both a hardware and software component, has been around for years. It made its automation debut when companies began installing programmable controllers to manage independent parts of the factory floor. As control technology evolved, the idea of islands of programmable control was discarded in favor of larger, centralized controllers. Industry is now moving back to a decentralized approach in which small, intelligent controllers gather data locally and share it across a network.

Figure1: click for larger image

Trends in HMI systems have followed the same ebb and flow. Early HMI stations permitted both viewing and control of individual machine operations or manufacturing processes. The HMI architecture then evolved into that of one computer networked to multiple programmable controllers and HMI viewing stations (see Figure 1). In this design, the “intelligence” rests within the single central computer, which performs all of the HMI services including program execution.

Recent technological advances have allowed companies to move from a centralized HMI structure to a true distributed architecture. Distributed HMI connects multiple HMI servers to each other, and allows each to communicate with multiple remote client stations.

Software sets the standard
Software advances are the key enablers of distributed HMI. Unlike Rockwell Software RSView32™, which was built to run on Microsoft Windows NT, the RSView™ Enterprise Series products were built to run on Microsoft Windows 2000 and Windows CE, taking advantage of Microsoft’s latest technology.

Windows 2000 Terminal Services, in particular, lets users install an HMI application on a central server and execute it in multiple client locations over virtually any type of network connection. This greatly eases maintenance chores, because users don’t have to reload software on each client when something changes. The clients merely access the software housed on the server. Other benefits include reduced network traffic and increased application security.

When combined with ACP's ThinManager software, Rockwell Software’s RSView32™ Active Display System andWindows 2000 Terminal Services lets Rockwell Automation customers centralize HMI operations and deploy clients throughout the plant. The RSView32 Active Display System supports up to 20 clients and allows independent access to information, viewing screens, the server and the process.

Today’s distributed HMI solutions make additional use of industry standard technologies and open architectures. For example, Microsoft inspired a revolution within the manufacturing industry by allowing companies to use off-the-shelf operating system features to take advantage of Ethernet networking and increased reliability. Citrix Systems is another company that has improved server software. ACP took products from those companies and combined them so that users can now run applications on practically any device over any connection, including both wired and wireless.

Hardware helps too
Typically located off the factory floor, an HMI server is a high-end computer with enough memory to store and execute the HMI software programs. The server’s more computer-friendly location means more expensive, industrially hardened components are not necessary. However, many manufacturers do recommend adding hardware redundancy and uninterruptible power supplies to protect the integrity of HMI applications.

On the client side, the distributed HMI architecture eliminates the need for full-powered stand-alone computers. Because they do not run high-end, resource-intensive HMI software locally, these “thin clients” need little in the way of RAM, disk storage capacity and CPU speed. Commonly, the client is a basic computer, such as an Allen-Bradley RAC6181™. Additionally, Rockwell is working with ACP to bring to market several other ACP Enabled Thin Clients in the coming months.

Next-generation HMI
For Rockwell Automation, the key to distributed HMI is Rockwell Software RSView™ Supervisory Edition, scheduled for release this summer. As the next generation of RSView32 component-based HMI software package, RSView Enterprise Series products are based on a new scalable architecture, and serve as the foundation for Rockwell Automation’s ViewAnyWare™ strategy. The goal of ViewAnyWare is to provide a common development environment, application reuse and an integrated architecture so customers can increase productivity, reduce operations costs and improve quality.

The transition to multiple servers and multiple clients eliminates the one risk—a single point of reliability—associated with the centralized intelligence/distributed viewing approach to HMI. The built-in redundancy of the distributed HMI model means that the failure of one server has a minimal impact on the overall system. Another server can take over HMI program execution, users can get information through any plant floor client, and the process continues to operate. And when combined with automatic server failover and redundancy found in ACP's ThinManager software, the customer ends up with the ultimate in reliability.

The future of the HMI
The evolution of HMI software has increased opportunities for manufacturers to take control of processes across their enterprise, applying a common development environment and functionality to both individual machine-level interfaces and fully distributed supervisory-level HMI stations. Improved software development tools are making it possible and more cost-effective to build upon the distributed HMI architecture and allow users to gather information from the factory floor.

By adopting a distributed HMI architecture, businesses will benefit from the added efficiency, flexibility, and freedom to access and control information from various areas within the enterprise. Companies around the world have recognized the power of real-time data and decision-making, committing billions of dollars to this innovative model that will reap billions more in profits and savings. It is a critical technological advantage that business must embrace to avoid being left behind.