High-power trunk concepts for fieldbus:
FuRIOS becomes a reality
High-power trunk concepts, i.e. topologies with high power in the field, are according to renowned users the breakthrough in fieldbus connection technology. Figure 1 shows the corresponding sheet from the fieldbus experience reports which were presented by DSM, Novartis and Sanofi Aventis as well as Mr. Schwibach from BASF and leader of the NAMUR working group 2.6 “Fieldbusses” at the NAMUR general assembly in November 2004.
Figure 1: Summary of fieldbus experience reports at the NAMUR general assembly 2004
New Perspectives for Users
We at Pepperl+Fuchs do not consider this to be anything particularly new. We have been talking about the FieldConnex® FieldBarrier and the Ex e/Ex i power feed concept for more than three years now. However, only now after the first major process produuction plants have successfully gone into operation on the basis of the FuRIOS recommendations of 2002, are the users starting to free themselves on a larger scale from the traditional explosion protection concepts. Figure 2 shows this “old” approach in which intrinsically safe power supplies or segment couplers imposed energy limitations with its corresponding restrtictions on the entire fieldbus segment.
Figure 2: Intrinsically safe fieldbus according to the “old” concept
High Energy for the Trunk—Limited Energy for the Spurs
The starting point for high-power trunk concepts is the question at which points maintenance work could become necessary in a system during live operation. These are the field devices and their spurs which should be correspondingly designed with an intrinsically safe Ex i explosion protection. Intervention to the passive cabling, i.e. the fieldbus distributors and the trunk to the host, is rarely necessary. Therefore the passive cabling should be carried out in the protection method “increased safety” Ex e. Additionally: if a fault on the trunk should ever arise, the connected field devices will not function anyway. This, on the other hand, is extremely unlikely due to the mechanical protection specified for Ex e. Ex e does not permit any intervention during live operation, but enables high power to be fed into the explosion hazardous area and thus the fieldbus to be fully exploited. The corresponding fieldbus distributor, namely the FieldBarrier, is in charge of transition to Ex i.
The growing market acceptance for high-power trunk concepts for zone 1 is not only evident from the increasing interest of the users. The major manufacturers, who to date have supported the concepts in figure 2, have in the meantime started to introduce fieldbus barriers.
Solutions for Zone 1 and Zone 2
But Pepperl+Fuchs is already one step ahead: the Power Hub System offers new, optimised functions and protective features which help increase the overall plant availability. The details are available in an article published in the P&A magazine (“Fewer Handicaps in Explosion Hazardous Areas”).
And the next step has also been taken: FieldConnex Segment Protectors are Ex nA[L] certified. This permits high-power trunk topologies to also be set up in zone 2, meeting the reduced safety requirements. In the same way as for Ex e/Ex i in zone 1 the trunk is ”non-sparking” Ex nA while the field devices are connected at the outputs of the Segment Protectors with limited energy Ex nL. By configuring the Power Hub System with various output voltages and correspondingly certified field devices topologies can be optimized for almost any application.
