Control system architectures: Remote control

Standalone systems can become DCS-like by adopting some of the DCS-based  technologies, such as fieldbus, says Jonas Berge, marketing manager at SMAR. “For package units and similar systems, users don't mind a small control system, but increasingly they want package unit controls to tie in with the main control system digitally, not via hard wire,” he says. “Standard application layers for industrial Ethernet are helping to make this possible. A good example is FF-HSE [Foundation fieldbus high speed Ethernet—ed.]. Several control systems now support FF-HSE as a control network thus making such integration possible.”

Berge also believes that OPC-based systems are a good way for standalone systems to reach servers. “Users can best prepare themselves by investing in control systems that have open platforms,” he advises. “The system's software architecture should be based on OPC, rather than being proprietary with a gateway ‘application station’ to OPC. Migration from DCOM-based OPC to OPC-UA is expected to be smooth, enabling users to take advantages of web services such as server-based systems.”

Another way is to install DCS-based HMI/SCADA software in the standalone system’s PC. Software such as Wonderware’s InTouch, for example, can easily link a standalone PLC or PAS to a host of advanced IT functions typically offered by the big DCS vendors.

DCSes Understand Servers
While standalone systems must reach out to a host of suppliers to find the enterprise-level support that Honeywell’s McGeorge notes above, modern DCSes already have it. Virtually every DCS vendor supports a wide range of enterprise-level software. The vendors either have their own packages, or they have made agreements with software vendors. Most importantly to DCS users, the integration of all this software is transparent. If you need condition monitoring or a process historian, it just plugs into your existing system.

Because functions such as asset management, condition monitoring, process historians, and all the other IT-like tasks are contained in one or more separate workstations, these workstations are performing the functions of a server. They just happen to be resident in the plant, and they only “serve” one user or process.

“Many suppliers are using the client/server model for HMI,” notes Bruce Jensen, manager systems marketing for Yokogawa. “Not only does that facilitate local control, but also remote access as well.  The downside is that graphics and data are managed by single PCs.  Yokogawa uses peer-to-peer operation and monitoring operator stations which are independent, but augment with a client/server specifically for remote access.”

All a server-based DCS does is move those IT functions elsewhere, and connect to them via Ethernet, private networks, microwave or some other medium. Some services – such as condition monitoring, advanced loop tuning, and process historians— are already being “farmed out” by plants worldwide. In other words, some end users are already employing remote server technologies, in spite of their alleged resistance to letting outside entities process their data.

Server Systems at Work
We know that most major DCS vendors support server technology, and all of them are capable of providing remote servers. Four years ago (May 2001, p 31), we reported on how Siemens provides a remote server-based system for foundries in Germany, where a host of enterprise software is available on a per-use basis over the Internet. Because the foundries don’t have to buy ERP, asset management, and similar software, they save about 70% in overall costs. It also illustrates that a number of different companies – all competitors, in this case – are willing to use a common “information utility” to gain access to advanced software for minimal expense. That puts paid to the argument that user companies won’t subscribe to such a service.

Honeywell also has server systems in the field, according to McGeorge. “We have one pharmaceutical customer who has implemented a control system architecture with 12 redundant servers distributed and integrated through Honeywell's Distributed System Architecture (DSA),” he says. “Several years ago, we deployed our system in ASP style over the public Internet using VPN technology to monitor multiple utilities.  Due to the efficient communication regimes we use and open protocols, this was accomplished without any difficulty.”

Nevertheless, only two vendors supplied specific information about server systems used for control and monitoring: Wonderware/Invensys and Emerson Process Management.

Wonderware, in fact, is supplying server based systems to several companies, including the London Underground, Nutramax (Gloucester, Mass.), DMS Powders (South Africa), Kansas City Power & Light (Kansas City, Mo.), Yellow River Conservancy Commission (China) and Arla Foods (Christiansfeld, Denmark).

“Some end users are already employing remote server technologies, in spite of their alleged resistance to letting outside entities process their data.”

The Arla Foods installation involves using Wonderware’s ArchestrA, IndustrialSQL and its other server-based software products on the plant side with SAP’s NetWeaver ERP system on the business side. he system obtains real-time information from Arla’s widely scattered 70 dairies and processing plants, and makes the information available to company personnel in a central location. “The program calls for all of the systems within the Arla Foods organization to be integrated into a single system,” says Jorgen Greve, plant manager at the Christiansfeld Dairy Centre. “This will make it easier for our corporate headquarters to follow up on business operations on a regular basis.”