The trunk-and-spur topology is accepted and often used. It is the de facto standard in process automation with fieldbus, because it is easy to engineer and easy to manage. A trunk-and-spur topology is made of power supplies and fieldbus couplers. Spurs are certified for your intrinsically safe instrumentation.
Your instrumentation connects to the fieldbus coupler, the DART Segment Protectors. The Segment Protectors are certified for installation in Zone 1 with outputs that are certified intrinsically safe Ex ib IIC. DART protects your plant from the very explosive gasses of group IIC. This means:
The DART Segment Protector provides sufficient power for device connections. Most importantly, it provides the short-circuit protection, which is critical when live maintenance is required on an instrument.
Up to 1000 m of homerun/trunk is permitted with DART Fieldbus. Up to four DART Segment Protectors can be connected to the trunk and provide devices with intrinsically safe power. Spur length is on top with up to 120 m per spur - double the length of FISCO. This is very similar to the High-Power Trunk today.
The table highlights the most important technical attributes of DART Fieldbus. With most attributes influenced by the fieldbus standard (IEC 61158-2), fewer regulations apply for fieldbus in Zone 1 compared to FISCO or the High-Power Trunk.
|Trunk output power||typ. 22 V / 360 mA|
|Spur output power||min. 10.5 V @ 34 mA|
|Impedance – Cable type: ’A’||100 Ohm|
|Trunk cable length, max.||1000 m|
|Overall cable length, max. (as per IEC 61158-2)||1900 m|
|Spur cable length, max. (as per IEC 61158-2)||120 m|
|Entity parameters for instruments Uo, Io||24 V / 250 mA|
|Trunk length and number of devices all depend very much on the topology and instrumentation you choose.|
DART Fieldbus is planned like any other fieldbus segment. Explosion protection almost “comes for free” with very little effort and giving you greatest choice and flexibility on designing fieldbus segments. Planning means to you:
Only a few limitations apply due to constraints for explosion protection. The rest is “just fieldbus”. The developers of DART Fieldbus have taken great care to engineer the components and explosion protection so that your planning and application of fieldbus in the hazardous area is simple.