Profibus System Integration PDF 4.03MB - Schneider Electric

Multi-barriersxDP/PAcouplerSegment outPROFIBUS-PAZone 1xEExeZone 0EExeTrunk inTrunk outWhith the need to handle a number of devices in an explosive area, and consideringthe population limitation resulting from a conventional intrinsic safety layout, onepossibility is to install as many Transparent Segment Couplers as required, based ona rough calculation of 1 coupler for every 9 devices see previous example.Another possibility is based on a multi-barrier (also called "field-barrier") concept.The idea governing this approach is quite simple:• Because the current requirements of individual devices cannot be decreased,more devices results in a higher total current.• With a higher current delivered to the junction boxes, the intrinsic safety protectionmethod is no longer adaptable for the trunk line, in explosive area• As a result, an increased safety protection method (Ex e) is providedUsing this concept, the trunk line is routed thru cascaded junction boxes named"multi-barriers". Respecting proper installation rules (terminals, cables and ducts),and with no ability to execute maintenance on the "Ex e" trunk line during normaloperation, this approach allows for a trunk current of up to 10 A. As a result, supplyingup to 32 intrinsically safe stations (according to IEC 61158-2 standard) in theexplosion-hazardous area is now possible.29