Break Through: Fieldbus Protocols

Fieldbus Protocols Continue Pushing into Mainstream Process Applications, and Innovative Users Are Forcing Their Network Infrastructures to Evolve Along with Them

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"Many process plants are embarking on real fieldbus applications for the first time. Fieldbus is a truly enabling technology, but its installation involves some additional considerations over and above traditional 4-20 mA systems. Up-front engineering is key to the success of any fieldbus project, and end users must be mindful of physical layer requirements such as power conditioning and segment termination," says Jeff Marsh, FeedForward's senior project manager. "Without correct connection of wiring and field devices, any anticipated ROI from fieldbus technology can be wiped out because technical complications can delay setting up a plant and take a long time to recoup in operational savings."

To prevent performance and reliability problems caused by bad or over/under terminations, short circuits, interference and inadequate grounding, engineers at Abengoa's Ravenna plant decided to specify new device couplers with automatic segment terminators and short-circuit protection. These couplers simplify fieldbus installation, reduce time required to install and troubleshoot field devices, and assist in segment commissioning by eliminating manual termination. As a result, FeedForward installed MooreHawke's (www.miinet.com) Trunkguard system, which is reportedly the first FF and Profibus physical layer solution with automatic fieldbus segment termination. Abengoa's control system incorporated 72 individual fieldbus segments with more than 650 nodes, which were installed using MooreHawke's field device couplers, redundant fieldbus power supplies and segment power conditioners.

"Trunkguard provided seamless plug-and-play connection with the Yokogawa DCS. The control system's H1 cards connected directly to the power conditioner boards, eliminating the need to manually wire each fieldbus segment" explained Marsh. "Unlike the older current-limiting technique, Trunkguard's short-circuit protection prevents segment failure caused by single device faults. Its "fold-back" technique automatically removes the faulted device from the segment, and doesn't permit any current flow to the device until the fault is corrected. The fold-back technique employs a logic circuit on each spur, which detects a short in an instrument, disconnects that spur from the segment and illuminates an LED visible to maintenance personnel."

Tom Wilson, Abengoa's COO, adds that the Ravenna plant's fieldbus-based DCS will give its ethanol process long-term competitive benefits. "Fieldbus provides us with a leaner automation architecture containing less wiring and hardware than a traditional control system. Loop and wiring diagrams, panel drawings and cable schedules were greatly simplified. Plus, installation was easier than with a traditional system, since several devices could be multi-dropped on one pair of wires," says Wilson. "The flexibility of fieldbus also allows us to reconfigure our process automation scheme to meet product and sales demands without major reinvestments. It reduces I/O subsystem requirements and makes the plant control system very scalable. The system can be expanded or modified loop-by-loop as needed. Thanks to our fieldbus automation solution, our Ravenna plant has achieved optimal operating conditions that increase yields, while also cutting the amount of energy needed per gallon of ethanol produced."

Similarly, HiProm Technologies (www.hiprom.com), a system integrator in Johannesburg, South Africa, reports that its mining and metals processing clients are using more Profibus, Foundation fieldbus and other digital networks in their platimum, gold and coal mines, shops and steel fabrication plants, but they had to first overcome some network difficulties and reluctance (Figure 2). Its clients include Anglo Platinum's Rustenburg mining operations and Impala Platinum.

"It was the classic integration problem—it was hard to bridge the gaps between the existing network and the fieldbuses," says Hein Hiestermann, HiProm's CEO. "However, this has become easier over time with better communication devices, such as the EN2PA module we invented that links EtherNet/IP to Profibus PA."

Stephen Proctor, HiProm's technical director, adds that HiProm has been making modules with help from Rockwell Automation (www.rockwellautomtion.com) for years, but adding Profibus meant writing firmware to make a Profbus PA device look like an Allen-Bradley I/O device. This eliminates the need for the array of devices previously needed to connect foreign networks and controllers, he explains. "This method makes configuation and automated operations a lot easier," says Proctor.   

Gateways, Subnets and the Future

Ironically, as fieldbuses replace hardwiring and as linking devices and gateways make it easier, there's probably no way to avoid basic changes in how industrial networks are designed and implemented. Few observers think traditional control rooms will disappear, but there's sure going to be a lot more data processing and value-added jobs going on ever further out in the field.

"We're actively involved in working with suppliers to expand the application of Foundation fieldbus," says Saudi Aramco's Kinsley. "We're working toward adopting FF in both our SCADA and safety instrumented systems. This will increase the overall percentage of digital bus technology at our facilities and reduce training and spare parts requirements. In our SISs, Saudi Aramco is conducting a beta test for FF-SIS, which will be one of the world's first field installations of this technology. We believe there will be greater adoption of FF-SIS once it's sufficiently mature. We also see great benefit in SCADA applications where remote diagnostics can significantly reduce maintenance time by limiting travel.
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