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Fieldbus topology for IS installationsIn general the same arguments apply for ISinstallations in regards of grounding; shielding; protection etc.In addition the topology has to provide the ISisolation between safe areas (e.g. control room) and hazardous areas (e.g. field).As fieldbus devices are low power devices anyhow, IS is a very appropriate method for fieldbusinstallations in hazardous areas.Today two different IS installation concepts for fieldbus are existing:
“True intrinsic safety“-Concept“High Power Trunk“-Concept
“True Intrinsic Safety”-Concept and “High Power Trunk”-Concept are both widely accepted and have to be seen as prooventechnology.What about a “True Intrinsically Safe High Power Trunk”-Concept?In other words: Can we achieve high power on an intrinsically safe trunk?
Single Ex-i harzadous area protection concept, no Ex-e wiring.High Power Trunk offers more cable length through accepting bigger voltage drops along the trunk cable.Simplified Active Junction Box (compared to Fieldbusbarrier).Spurs remain FISCO protected.
The energy in an intrinsically safe system is limited to a value that is not capable of causing ignition in normal operation and fault condition in the surrounding hazardous atmospheres by sparks (opening, closing, short circuit, short circuit to earth)