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Protection for fieldbus devices

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THE TG200 TRUNKGUARD Series Fieldbus Device Couplers from MooreHawke, a division of Moore Industries- Pacific Inc. , use a unique "fold-back" technique to disconnect a shorted instrument from the fieldbus segment, thus preventing complete segment failure.

Other fieldbus device couplers use a "current-limiting" technique, which holds a fault on the segment; this adds up to 60mA of current, which may deprive other instruments on the segment of power, overload the segment power supply, and cause an entire segment to have catastrophic failures.

The fold-back technique used in the TG200 has a logic circuit on each "spur" that detects a short in an instrument, disconnects that spur from the segment, and illuminates an LED that can be seen by maintenance personnel. By removing shorts from the fieldbus segment, users have confidence that wiring and instrument mishaps will not jeopardise their fieldbus segment reliability and availability. No other fieldbus coupler has this fold-back feature.

The TG200 Device Coupler also simplifies commissioning and startup through use of a patented Automatic Segment Termination feature that eliminates problems caused by over or under-termination.

The Automatic Segment Termination feature in the TG200 series of device couplers automatically activates when the device coupler determines that it is the last fieldbus junction device in the segment; if it is, it terminates the segment correctly.

If it is not the last device, it does not terminate the segment, since the downstream device coupler will assume that responsibility. No action- such as setting DIP switches- is necessary by the installation person to terminate a segment properly.

If a device coupler is disconnected from the segment accidentally or for maintenance, the Automatic Segment Termination detects the change, and terminates the segment at the proper coupler. This allows the remaining devices on the segment to continue operation. No other fieldbus device coupler has this automatic segment termination feature.

TG200 device couplers are available with four, eight or ten fieldbus spurs, and work with FOUNDATION fieldbus H1 and PROFIBUS PA interfaces. Couplers can be DIN-rail mounted or enclosed in IP66-rated glass-reinforced polyester (GRP) or stainless steel enclosures.

Up to 32 fieldbus devices can be accommodated in a single segment. The TG200 TRUNKGUARD has ATEX/FM approvals for use in Zone 2 and Division 2 hazardous areas. Other TRUNKGUARD models are available for other hazardous area classifications or other protection concepts.

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