|
|||
 
|
       |
||
|
 |
 The great migration – Field bus integrates Ex-protection, SIL and analog signalsThe field bus is being used ever more frequently in process automation. Restrictions due to the requirements of explosion protection are no longer a theme and the new protocols for safety-aligned field bus applications are resulting in parallel-wired analog safety systems becoming superfluous. So no problem for new plants on green field sites. But what about the many existing plants with analogue signal transmission? Here the integration of remote I/O technology in the field bus offers an ideal platform for migration and plant extensions.  Pepperl+Fuchs Fieldbus Technology "Field bus technology has proved to be extremely helpful in keeping to the tight schedule for the construction of the Clariant ruby plant" [1]. Clearly, these three notable users of process automation technology, and in the meantime many others [4], are convinced of the advantages of modern through going digital data transfer from the field devices to the control system using PROFIBUS PA and FOUNDATION Fieldbus H1. In the past, solutions have had to be found for several areas of doubt, which were formulated in the 2002 FuRIOS Study [5]. But now, in 2007, we have the answers to:
High Power Trunk Concept – the end of the power shortage Explosion protection through intrinsic safety limits the energy in the signal circuit in such a way, that no explosion-causing sparks can be generated. That which presents no problem in a conventional loop with a field device, a cable and an Ex i barrier, is simply impossible in the field bus network with up to 31 devices and a cable length of 1900 m. The solution was presented at NAMUR in November 2004 [2]: Field bus barriers. These distributors provide an intrinsically safe connection for each field device, which in addition is individually protected from short-circuiting. The connection between the barriers, the so-called trunk, is designed to provide increased safety (Ex e), which enables the injection of high energy in Zone 1 (Figure 1). Corresponding high power trunk concepts for Zone 2 are also possible through segment protectors with connections in Ex nL (in future Ex ic) [6].  High Power Trunk Topology, also for SIL applications Safety-aligned field buses – doing away with parallelism On all previously constructed plants conventional wiring for safety purposes has had to be installed parallel with the field bus network. This will not be the case in the future. For PA and H1 protocols have been developed up to SIL 3 [7], based on NAMUR Recommendation NE 97. The user tests are running, soon process and safety signals will be transferred in perfect harmony via a common field bus cable. And the good news is: The installation technology is not subject to any SIL consideration! Planning and maintenance – drag & drop with online diagnosis It was often feared: Planning and maintenance changes significantly with the field bus. This is true – both are significantly simpler! The layout of a field bus segment can take place virtually on a PC, including the automatic calculation of the energy balance, simulation of fault cases and the generation of equipment lists. Software design tools, such as the Segment Checker, which is available, free of charge on the Internet (www.segmentchecker.com) offer extensive device libraries, from which the segment can be assembled with a few mouse clicks. High availability required – the answer is redundancy In 2004 redundant field bus components [2] were called for at the NAMUR main assembly. Today they are available: PLC with redundant field bus cards, power supplies, such as the FieldConnex® Power Hub with modular replaceable, redundant power modules [6, 8]; the first systems with trunks aligned parallel in the field were presented at the Interkama exhibition 2006.  FieldBarriers and Fieldbus Process Interfaces Analog signals – no problem with field bus process interfaces In existing process plants there are millions of analog and binary field devices in use, which, understandably, one doesn't want to lose. This led to the development of field bus process interfaces, which bundle the signals from many sensors and actuators into a single field bus message and thus integrate them efficiently into the digital communication (Figure 2). So, for example, the FieldConnex® Temperature Multi-Input incorporates the values form eight temperature sensors. On modern field bus remote I/O Systems, like the LB/FB Series, almost all analog field devices can be connected. The modular construction of these systems enables optimum matching to any process plant. Migration strategies can be developed for the successive modernization of existing plant in conventional technology towards full field bus communication [9]. Literature
Our Products |