To upgrade or not to upgrade—that is the question today’s dour economy is forcing many manufacturers to ask themselves about the old analog sensors and instrumentation in their plants. They often wrestle with the question for a while, looking for evidence that installing digital technology will squeeze more from their processes to improve their competitive positions. “These end users are in the middle of a migration and modernization crunch,” says Larry O’Brien, global marketing manager for the Fieldbus Foundation in Austin, Texas.

What can make these decisions particularly difficult is the strategy. Do you simply enhance the current infrastructure with digital devices, or do you adopt an entirely new control strategy?

Questions about the control strategy factor into any decisions about upgrades because, like the sensors and instrumentation, the control systems can be more than 20 years old, too. Boston-based ARC Advisory Group estimates that the installed base of process automation nearing the end of its useful life is approaching $65 billion. For this reason, O’Brien sees any move to modernize as a good opportunity to plan for migrating from the conventional 4-20mA infrastructure to a fieldbus architecture.

He believes that replacing the entire system, both instrumentation and controls, with a digital communications network is well worth the effort and expense. “You get to see your process in ‘high definition,’ ” he explains.

“Foundation Fieldbus devices allow transmitting multiple values and a huge range of diagnostic information that is simply not available with any analog-based technology.” Some manufacturers find that having more information can generate tremendous savings, not only in operations but especially in predictive maintenance.

“When used properly, digital technologies can provide far more functionality than their analog counterparts,” adds Todd Garner, vice president of sensors and communication, for Siemens Industry Inc.’s Industry Automation Div. in Alpharetta, Ga. Besides eliminating drift and boosting the accuracy of measurements, digital instrumentation and control can perform the complex functions that are necessary for diagnostics, safety, control, supervision, and monitoring in a plant.

Garner warns users, however, to keep the differences between the digital and analog technologies in mind in the planning stage. “In most modernization projects, it is not feasible to replace all instrumentation and control system components in the plant simultaneously,” he says. “Therefore, you have to pay special attention to the interaction between the existing systems and the new technology. In many cases, modernization requires more than just replacing existing systems by their digital equivalents, because the two systems are not necessarily functionally identical.”

A Hart for bioplastics
To avoid this, many users prefer to forego the enhanced functionality. Instead, they add digital communications to their installed base of 4–20-mA analog devices by turning to the Hart Communications protocol, which allows an analog signal to serve as a carrier of some digital data. An example is NatureWorks LLC, a producer of biodegradable plastics in Blair, Neb. Management there had decided to perform the upgrade when the company replaced an old, proprietary control system that was no longer being supported by its manufacturer.

The process for producing plastics from sugars extracted from corn and other plants received a new distributed control system (DCS) from NovaTech LLC’s Process Control Div. in Owings Mills, Md. “After choosing our D/3 DCS, the company’s engineers determined that they preferred Hart field instrumentation because it is easily connected through the D/3’s 8000 Series Ethernet I/O modules,” says Joe Shingara, director of product marketing at NovaTech.

Besides the ability to get service from a variety of sources, a chief benefit of using these intelligent devices is the communications established by the Hart protocol and input/output (I/O) modules. Not only does FieldCare asset management software from Endress+Hauser Inc. of Greenwood, Ind. detect and populate the asset database automatically, but it also gives NatureWorks engineers access to all field devices connected to the DCS. Engineers and technicians, therefore, can configure and manage these devices remotely without having to travel to the site and climb on scaffolds. “I was actually able to do it offsite from my desk,” reports Don Marek, president of Plant Services Inc., the Omaha-based consulting firm that installed and configured the instrumentation.

“The new technology also makes maintenance easier,” Marek adds. Not only can operators monitor the process from the control room, but they also can monitor the health of the sensors and instruments themselves. Every time a Hart device responds to a request for information, it also sends six bits about its status and condition, thereby reporting key performance indicators about itself. Operators can dispatch ...