While the use case for off-line, on-demand HART connectivity is compelling, further leaps in plant productivity and reliability await users who pursue full-time, integrated HART connectivity among their field instruments and control and asset management systems.
With off-line HART, the emphasis is on bringing productivity and efficiency to routine and reactive maintenance tasks. But with full-time HART connectivity, users can begin to leverage the HART Protocol's diagnostic power to drive predictive methodologies that can both reduce maintenance costs and improve plant reliability. Integrated HART connectivity also allows instrument and host system manufacturers to implement new synergistic features and functionality not possible over a simple 4-20mA connection. And despite its many years of widespread, proven use, "many people are still unaware of what's possible with HART," notes Scott Saunders, chief operating officer for Moore-Industries International. "HART Communication is about more than just the handheld."
Robert Schosker, Pepperl+Fuchs' product manager for the company's HART interface products in the Americas, notes that all talk about the potential benefits of wireless technology these past several years -- and fieldbus before that -- has served to remind users of the value proposition HART has always offered. "The push toward wireless, fieldbus and other digital networks got people to think more about that extra information they could get back from their devices. For users who say ‘I'm not ready for fieldbus, but we have all these HART devices around,' the move to [permanently
integrated HART connectivity] is still a step forward.
Further, the large installed base of HART-based field instruments in many process plants means that integrated HART connectivity need not be an overly ambitious, all-or-nothing proposition. A first step might be extracting and translating a handful of critical HART diagnostics into digital or analog I/O signals for alarming in an existing control system. In a stepwise fashion then, users can tackle as much HART connectivity as is practical with little risk and tremendous upside as they learn the benefits.
Alternatively, multiplexers provide a relatively straightforward way to pluck HART signals from existing analog I/O cards and wiring without disturbing the current control system installation. For example, a HART interface module can effectively extract the extra process variables gathered by today's increasingly powerful multi-variable transmitters, says Chris Costlow, Yokogawa business development manager for meters and instruments.
And if your plant is among the many out there with an aging control system that must soon be replaced, most modern control systems on the market today offer out-of-the-box HART connectivity at the I/O level that can be used directly in control system strategies or passed through to a complementary plant asset management system, offering a speedy return on a small incremental investment.
Ray Azizian, technical support engineer in Yokogawa's VigilantPlant Services group, notes that while handheld devices have their role, especially for use in hazardous areas, integrated connectivity offers significant visibility benefits. For example, with the company's Plant Resource Manager (PRM) plant asset management software, "you can look into assets and HART devices from the comfort of your desk or maintenance shop," he says.
Diagnostics Drive Reliability Gains
At the Dow Chemical Company's complex in Deer Park, Texas, HART-based diagnostics have helped slash plant trips attributable to instruments and control valves by 70% over the past three years, delivering "millions of dollars in savings," according to Dow's Shadrach Stephens, instrument reliability engineer, and Christopher Garcia, instrument/electrical technology leader.
In order to prioritize their efforts, Stephens and Garcia first analyzed sources of downtime and found that five reactors accounted for a full 48% of instrument- and valve-related outages. "We needed to identify the opportunity so we could justify the return on capital to our leadership. Where could we make the biggest bang for the buck?" Stephens says.
Their first priority was to deploy continuous monitoring via HART for the plant's most critical control valves, which also were the biggest contributors to downtime. The plant now uses HART connectivity to Emerson Process Management's AMS Suite software to help mitigate failures but also to push out preventive maintenance intervals, Stephens says. "We can proactively work with operations to resolve issues without incurring downtime."