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"If you have a lot of HART devices in your installation, and you're not monitoring them on a continuous basis, you're missing a great deal of opportunity,” says Tom Holmes, president of MACTek, a manufacturer of HART modems. “There's diagnostic information, alarms, alerts and confirmations of whether the analog signal is good or bad."
Industry experts recommended a number of strategies to help users identify the most high-value applications involving continuous monitoring.
Emerson’s Cobb suggests that plants go about taking advantage of HART gradually.
“One of the nice things about HART is that you can add its capabilities to your plant, loop by loop, and gradually take your facility from analog to a fully integrated HART plant,” says Cobb.
“I’d start with online monitoring of my most critical assets. That’s where I’m going to get the most value from predictive diagnostics, such as being able to avoid unplanned shutdowns and preventing off-quality products,” adds Cobb. “At the same time, I might start using HART to monitor other instruments offline and gradually, as my maintenance budget allows, bring other assets online.”
Marcelo Dultra, vice president of sales and marketing for Smar International, recommends plant audits as a means of identifying areas ripe for improvement via HART. “They should do a full check of what equipment they have installed and what technologies they’re using. This kind of thing usually takes a maximum of two or three days,” says Dultra, who adds that Smar, as well as other vendors and consulting firms, provide such services.
"It's always good to get opinions from outside the plant, from people who have seen other operations. If you work a long period in your own plant, you miss some points that are important, especially when it comes to the technologies available today,” he adds.
Prasad Raghavendra, Honeywell’s product manager for all systems-related HART products, recommends that users review a history of process upsets and their causes to identify areas that are ripe for HART-enabled continuous monitoring. “Make a business plan out of that to determine if the cost of incidents are higher than the cost for investing in HART-enabled I/O,” says Raghavendra. “That’s a fairly simple method that would clearly indicate whether it was worth it for the customer to make the investment.”
In some instances, he says, the benefits from investing in HART will be plain. “For example, your plant could be having problems caused by simple incidents like sensor failures. If you’re simply relying on a 4-20 mA signal, the operator will see a local trip, but everything in that group of devices becomes suspect. This requires the operator calling maintenance and what could be an extensive debugging process. With HART, however, if there’s a sensor failure, the device tells you that it’s the source of the problem, saving you time and resources in correcting the malfunction.”
“Processes that could benefit the most from this technology are those with a large number of remote-connected HART devices that can be brought in to a control system through remote HART I/O,” says Eric Olson, a senior product manager with ABB. “This could include processes such as those in the oil and gas or wastewater treatment industries, where there are many satellite I/O stations.”
Foxboro’s Piper recommends that users employ a diagnostic tool such as ExperTune’s PlantTriage, to monitor loops and field instrument performance and identify potential troublespots that could benefit from full time monitoring via HART.
HART can play an important role in refineries, mills and power plants that employ process safety systems. To maintain a system’s Safety Integrity Level (SIL) rating, safety system valves must be periodically tested to ensure that they will move if called upon in an emergency. Full-range tests can be conducted only during plant shutdowns, but these occur only every two to three years. However, by stroking a valve by as little as 10 percent, which does not disrupt a process, plants can ensure the reliability of their safety valves. A valve positioner has the ability, via HART, to confirm to operators that the valve actually responded to the movement command.
Robert Hotard, a product manager with instrument-maker K-Tek, also suggests that users take advantage of HCF’s expertise in planning HART-based projects. “The first thing I’d recommend to anyone interested in HART is to go to the HART Communication Foundation’s website,” says Hotard. “There’s a lot of information there that’s available to everyone and explains in great detail how to use the protocol and the benefits that are possible. I’m currently writing some manuals for K-Tek products, and in them I specifically reference the HCF website.”
Don’t Overlook Control Opportunities
While most facilities use HART for applications related to device configuration and maintenance, users also should look for opportunities to use HART data for process monitoring as well. For example, in applications where conditions such as temperature, pressure and levels change relatively slowly, users can reduce the number of instruments they need in the field by acquiring multiple variables from a single device. Hotard points to tank farms as being ideal sites in which to make use of HART for applications such as inventory monitoring.
In relatively small operations, users can set up set up modest, but effective SCADA systems that utilize HART technology, says Mactek’s Holmes. “You could continuously monitor up to eight points using a PC equipped with eight USB HART modems. That’s very do-able,” says Holmes. “For software, you could use a dedicated data acquisition package such as Wonderware’s InTouch software, or something as basic as a Microsoft Excel spreadsheet. “I think there are plenty of operations such as bakeries or small specialty chemical plants that can’t justify spending the money for a large control system. But with HART input and a PC, you can build yourself a quick and dirty DCS,” he adds.
Liberate the Genie
Having HART capabilities at your disposal, but not taking advantage of them, is like keeping the genie stuffed in the lamp. By carefully examining your facility, looking at the HART capabilities you already have, and carefully weighing the need for additional investments, you can take full advantage of opportunities for improvement.
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