Unique Split-Architecture Device Coupler System Doubles Number Of Intrinsically Safe (IS) Devices For Hazardous Environments

For two decades, distributed control systems (DCS) have enabled pharmaceutical plants to exercise precise control over their processes, especially given the more efficient communication protocols such as FOUNDATION fieldbus. However, limitations in installing multiple sensor and other control devices in hazardous environments have traditionally stymied pharmaceutical engineers and DCS integrators in their efforts to maintain tight control.

Now, a new split architecture approach developed by engineers at MooreHawke — a division of Moore Industries-International, in North Hills, California—goes beyond traditional FISCO (Foundation Intrinsically Safe Concept) operating parameters with a full 350mA per segment; enough to drive up to 16 devices — while still being intrinsically safe for hydrogen at the individual spur connection. Subsequently approved by the FM (US) and SIRA (ATEX) certifying organizations, this approach uses a field-mounted device coupler, and associated power supply with a safe-area interface.

“To get the most bang for the buck during our last expansion we utilized the MooreHawke RouteMaster system of power supplies and device couplers within our DeltaV DCS,” says John Hutto, Instrumentation & Control engineer for Boehringer Ingelheim Fine Chemicals in Petersburg, Virginia — part of the Boehringer Ingelheim group of companies, one of the world’s leading pharmaceutical corporations.

“Our plant has a fair amount of drums that hold flammables and open manways on reactors, and while we try to keep everything closed, there are certain instances where you need to manually have a flammable open to the air for a short time — that makes the area a Class 1, Division 1 area,” says Hutto.

The Routemaster(TM) system “enabled us to get in the neighborhood of up to eight devices per segment,” he says. We could have gotten even more, but we like to limit our devices to those that are part of the same control loop or system, per segment. With ordinary FISCO, we could have only used about five, and that would be the max'."

The split-architecture power supply steps around the complexity associated with FISCO circuits by the use of a conventional wire-wound resistor. The ROUTEMASTER also incorporates full AC/DC power conversion, simple linear power supply, and full galvanic isolation, with built in redundant supplies. Fewer components translate into greater reliability.

The high current made possible by split architecture device couplers and power supplies enables the connection of devices over cable lengths almost double that of FISCO — 1900meters for trunk lines and 120meters per spur.

"Within the building the longest trunk run was 400 feet, and out in the field the longest cable run we got into was 500 feet." says Hutto. "This helps because we always have one of these device couplers available that we can easily tie an instrument into within 30-40 feet of any given place in the plant. We can get right up there in the bay and minimize conduit and wiring runs to short distances eliminating clutter verses traditional wiring techniques."

For pharmaceutical plants, it appears that recent technological improvements have finally enabled IS segment capacity virtually indistinguishable from non-hazardous fieldbus implementations. For those who believe that "the product is the process," this improvement in device couplers will allow devotees to stay competitive well into the future.

Harry Wilson
NSM – MooreHawke
(972) 335-0176
hwilson@miinet.com
http://www.miinet.com


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