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Fieldbus Couplers Protect Automatically

Dec. 16, 2003

New Couplers Provide Electronic and Auto-Resetting Short Protection

Conventional fieldbus installations require two separate segment terminators that have to be manually set. And if there is a short circuit, today's protective devices typically allow high currents that can lead to other failures in the segment.

New TG200 fieldbus device couplers from Hawke Intl. address these problems, reduce specification effort for systems integrators, and ease the wiring workload for field installers by enabling fast and easy connection/disconnection of Foundation fieldbus and Profibus-PA devices. The couplers provide electronic and auto-resetting short-circuit protection with automatic segment termination for up to eight fieldbus devices.

"On detection of excess spur current, the unit reacts immediately to switch spur current to a nominal trickle-level rather than simply limiting that fault current to a fixed, and always higher, level," says Michael Neale, director, Hawke Intl. Fieldbus. "So-called 'current-limiting' circuits actually maintain high spur currents without clearing the fault, which can overload the segment power supply and lead to other failures within the segment. At the same time, current-limiting designs have to dissipate excess power internally, leading to a risk of internal overheating and further damage."

The low current is sufficient to power an LED to indicate where the fault is, and the couplers automatically sense and reset when the short is cleared.

The units also provide automatic segment termination via patent-pending end-of-line sensing circuits. "Any upstream TG200 unit can take over segment termination in the event of any downstream wiring failure," says Neale, "which keeps the upstream devices online."

Properly installed, the TG200 is approved for connection to non-incendive devices (Div. 2/Zone 2) and intrinsically safe (IS) devices (FISCO & Entity). They can be installed in EExe or Class I, Div. 1/EExd enclosures for connection to explosion-proof field devices. If required, TG208-DIN can be specified without enclosure for custom mounting. The couplers are available as complete packages based on Hawke GRP or stainless steel enclosures, with cable glands as specified to suit field wiring.

For more information call 281/445-7400, see http://www.ehawke.com/.

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