Their intelligence works quietly in the background, providing a level of diagnostics that helps companies manage all types of assets, including work-in-process. These devices process information locally, performing tasks from providing error codes to self-calibrating the valve positioners regulating the production of polyethylene terephthalate (PET) at Wellman Inc., a plastic-resins producer based in Fort Mill, S.C.

The intelligent positioners are vital to controlling the quality of the PET pellets made at Wellman’s Pearl River plant in Mississippi. They regulate the introduction and, hence, interaction of purified terephthalate acid (PTA) and monoethylene glycol (MEG), the two main reagents, in the reactors. Consistency is critical because final product is a flexible, clear plastic that is fast becoming the preferred packaging material for beverages and other fluids. Not only must the plastic have the specified strength, but it also must look good.

“Controlling the injection of PTA and MEG, from a small trickle to an almost gushing chemical flow, is very difficult, and very, very critical,” says Robert Goetzman, senior controls engineer at Pearl River. “The process must be precise and repeatable to maintain the quality of our plastics, whether for clarity or strength.”  

The Foxboro SRD991 Positioners from Invensys Process Systems, of Foxboro, Mass., operate pneumatic valve actuators from control systems and electronic controllers over the Invensys FoxCom field device protocol. If one fails, it sets off an alarm in the control room, which is based on Foxboro’s I/A Series automation. The operators there either shut down the PET line temporarily or bypass the failed valve while technicians replace the positioner, a task that involves unbolting and removing it and installing a new one.

Then the automatic self-calibration kicks in. “It enhances quality control by eliminating or reducing mistakes that might result from a technician incorrectly calibrating the positioner,” says Goetzman. This is critical, because a miscalibrated positioner will inject the wrong amounts of PTA or MEG and ruin an entire batch.

Using its FoxCom communications instrumentation, the positioner performs the necessary diagnostics automatically in two to three minutes and sends the results to the control room. “From my office, I can check the status of all valve positioners and transmitters,” says Goetzman. Because of the positioner’s ability to monitor and calibrate critical parts of the company’s processes, Wellman uses one everywhere it needs to control the opening and closing of a valve continuously—including a new line slated to boost the plant’s output of PET by 50 percent this year.

Intelligence at work

The most important development in field devices has been their growing intelligence—intelligence to sift through the mountains of raw data being generated to find useful information and send it automatically to where it is needed. Building this kind of intelligence into field devices is crucial if users are going to reap benefits from the data available to them these days.

“Information is a good thing, but too much of it is a bad thing,” explains Rick Gorskie, senior product manager at Phoenix-based automation controls vendor Honeywell Process Solutions. “If devices just deluge you with information that you can’t use to run your process better, then the effort is wasted.”

Two developments have made the growing intelligence on field devices practical, according to Richard Casimiro, director of development for measurement and instrumentation at Invensys Process Systems. The first is the enhanced firmware made possible by the continuing advancements in digital electronics. The second is the international open-communications standard promulgated by the Brussels-based Field Device Tool (FDT) Joint Interest Group for managing the configuration and flow of information between field devices and automation control systems.

The FDT standard differs from the OPC open communication standard by focusing primarily on the device’s configuration, thereby making it independent from the communications protocol and the software running the device or the host system. “By expanding communications to field devices, FDT allows for exchanging much more diagnostic-rich information than do device descriptors (DDs) or enhanced DD language,” says Casimiro.

The result is better asset availability and utilization. Not only do the on-board diagnostics perform health checks on the internal workings of the instruments, but they also can report richer information in real time. In the case of valve positioners, such as the ones used by Wellman’s Pearl River plant, “management can plan their maintenance better and be more proactive at keeping their assets healthy,” says Casimiro.

Soon, warehouses equipped with automated storage and retrieval systems will have the same ability with the photoelectric sensors monitoring their equipment. “These facilities are generally very large and ...