Fieldbus Installation Foolproof at Chemical Processing Plant

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Advanced device couplers simplifies FOUNDATION Fieldbus and PROFIBUS system installation with features such as Â?auto terminationÂ? and Â?short circuit protectionÂ?

We're pretty sensitive to the time it takes to get to market with our plants, so anytime we can save in construction or commissioning, that certainly helps us

Whether for new plant ramp up or expanding/upgrading an existing plant, those responsible for process management have increasingly turned from antiquated analog SCADA and DCS systems to digital FOUNDATION Fieldbus and PROFIBUS systems for operational reliability and interoperability. But to expedite correct installation and operation, many now rely on advanced device couplers to link devices such as temperature and pressure transmitters with the process control system.

The plant managers and engineers at Delta T Corp. of Williamsburg, Virginia, for instance, recently specified about two dozen device couplers for one of their new chemical processing plants. The MooreHawke device couplers used, offered by Moore Industries-International Inc., provide "second generation" attributes such as automatic segment termination for 4, 8, 10, or 20 FOUNDATION Fieldbus H1 or PROFIBUS PA devices.

"This was a greenfield facility, designed and built out of a corn field," adds Tim Gale, Senior I&C Engineer for Delta T Corp., which designs, enhances and integrates technologies for customers in the energy and chemical processing industries.

"We're pretty sensitive to the time it takes to get to market with our plants, so anytime we can save in construction or commissioning, that certainly helps us," continues Gale. "The MooreHawke device couplers worked well for us in this regard."

The MooreHawke units used offer advanced features reflective of recent device coupler developments. Its auto-terminator feature expedites start-up, for instance. In typical installations, troubleshooting termination issues can take days on a segment with the wrong number of terminators.

Second generation device couplers like MooreHawke’s employ unique "end-of-line" sensing circuits that provide fully automatic segment termination to ensure local segment parts will function if remote parts are accidentally disconnected.

"The auto-terminator feature helped prevent any wiring errors; it's almost foolproof," says Delta T's Gale. "Another big benefit of using these particular units is their circuit protection."

While older generation device couplers employ "current-limiting" when a short occurs on the spur between the device and the coupler, the usual "lock-in" load is 60 mA, and no less. The danger of locking in this much current is the risk of causing other devices to receive insufficient current, causing them to drop off the network.

The MooreHawke device couplers, however, use a fold-back technique which locks in a small 2 mA load -- just enough to turn on an LED light -- then removes the device from the segment. Once the short is removed, the coupler automatically resets the device on the network.

The short circuit protection helps the installation process go quicker. Once installed, modern device couplers like the MooreHawke units can improve the control system’s reliability through diagnostic capabilities beyond what fieldbus alone offers.

Each MooreHawke coupler, for instance, contains LED indicators to provide status checks at a glance. Intuitively, the red LED indicates a fault in the spur; green, an intact healthy spur. This status information extends to each spur, so for a 10-spur device coupler there would be 20 LEDs -- a pair for each spur.

"It did save us time -- and time is money," concurs Gale. "The pricing on the MooreHawke device couplers was more competitive than others. It did save some hard dollars up-front."

As those responsible for process management turn from outdated analog DCS systems to digital fieldbus systems, the payoff for plant managers investigating advanced device couplers, such as MooreHawke’s, will only increase.

For more information about the MooreHawke line of device couplers, distributed I/O, temperature sensors, transmitters, alarm trips and signal conditioners, contact Moore Industries-International, Inc. at 16650 Schoenborn Street, North Hills, CA 91343; telephone 1-818-894-7111 or visit http://www.miinet.com.

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