Device Couplers: An Essential Link for Maximizing Fieldbus Installations
Specifying the correct FOUNDATION Fieldbus and PROFIBUS PA device couplers can spell the difference between quick up-time and low maintenance, versus delayed start-up and downtime
(PRWEB) August 23, 2005 -- FOUNDATION Fieldbus and PROFIBUS are certainly popular, with installations in more than two-dozen countries. Yet, for all its operational advantages, it can also prove tricky to install. Without the correct connections, anticipated ROI can be wiped out as technical complications can delay setting up a plant and take a long time to recoup in operational savings.
For this reason, second generation device couplers have recently gained attention as an essential link that can make or break a new installation. In response, engineers and process control vendors are increasingly specifying device couplers that incorporate features such as auto termination, short circuit protection, and visual circuit checking as a means to ensure new installations proceed as planned.
"Having the right devices in the field is really important, as this can directly affect a business financially," says Chris Peters, an automation consultant with Logical Innovations, a leading DCS systems integrator. "If you have device couplers with features that enable you to start quickly, you're in much better shape."
As the vital link between devices, such as temperature and pressure transmitters, and the process control system, device couplers must excel at routing sensor inputs onto the bus toward the control head-end, and then routing commands back to the proper control devices.
In general, a second generation fieldbus device coupler reduces the design efforts of DCS systems integrators and the wiring workload for field installers by enabling fast and easy connection and disconnection of devices. Beyond that, the individual features of the unit can make a significant difference.
"Some of these features help you diagnose problems," notes Peters. "Other important attributes include auto-termination and short circuit protection. I like the MooreHawke device couplers because they have all of this."
Offered by Moore Industries-International (www.miinet.com), MooreHawke device couplers are complete packages based on IP66 field enclosures complete with cable glands to suit field wiring. The company's TRUNKGUARDTM units provide "second generation" attributes for 4, 8, 10, or 20 FOUNDATION Fieldbus H1 or PROFIBUS PA devices.
For example, the TRUNKGUARD employs unique "end-of-line" sensing circuits that provide fully automatic segment termination to assure that local parts of a segment will continue to function if remote parts are accidentally disconnected.
"The auto-terminator feature is the biggest thing that helps in start-up." notes Peters. "In most fieldbus installations it seems like you always have termination issues. You can spend 2-3 days troubleshooting a segment. But if you use the MooreHawke couplers that have the auto-terminator function, then you don't have to worry about termination."
Another benefit of the TRUNKGUARD is 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. Instead, the TRUNKGUARD utilizes a fold-back technique which locks in a 2 mA loadžjust enough to turn on an LED lightžand then removes the device from the segment. Once the short is removed, the device coupler automatically resets the device on the network.
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