New Approach to Power Supply Increases Fieldbus Network Design Flexibility in Hazardous Areas

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Simplicity in Practice Makes the Difference

The simplicity of FISCO inspired the designers of Dart Fieldbus to develop a new approach to intrinsic safety that would be equally simple in practice. Dart Fieldbus is designed with a comparable level of simplicity for planning and validation of intrinsic safety. Instrumentation and automation engineers need only observe three rules:

• Plan for up to 1,000 m of trunk cable. This is longer than required by most systems;

• Install only cable type A, a shielded twisted-pair cable that is common in fieldbus installations and is very resistant to noise induction;

• On the trunk, connect only components listed on the certificate, such as power supplies and fieldbus couplers.

And with these simple rules, which in any case practically run in engineers’ blood, the segment is planned and its explosion protection validated. Connections for the control system and field instrumentation conform to the regular standards, so investments in existing field instrumentation are protected.

System availability is equally important. The Dart Power Hub comes with two power modules per segment. These are arranged in a unique redundant configuration that incorporates managed load sharing, so that in normal operation each power module provides half the load current. This is a small detail that makes a big difference; each module operates at its optimum power level, leading to lower heat dissipation in the control room cabinet.

Practice has proven again and again that it is not the cabinet space but heat production in the cabinet which limits the number of segments per cabinet. So Dart Fieldbus supports a dense cabinet layout, lowering capital expenditure. In addition, the electronics operate at their optimal temperature, which helps increase their service life.

Dart Segment Protectors, the fieldbus couplers, are certified for installation in Zone 1, so the junction box can be placed close to the field instruments. Dart Segment Protectors provide short-circuit protection at each output.

This means that maintenance performed on one device leaves the remainder of the segment untouched. Even the occasional short-circuit that happens when an instrument is connected or disconnected will not harm plant operation.

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