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 Plant Revamp using Remote I/OTwo Degussa production plants were to be revamped within a period of only two to three weeks without unduely interrupting production. The existing signal conditioning interfaces were to be replaced while all the sensors and actuators fitted to the pipes and vessels were to remain in tact. The Pepperl+Fuchs Remote I/O was ideally suited for the job ... Considerations concerning cost reductions play an ever growing part for both instrument manufactures and end users. The following paragraphs will show how Remote I/O can offer advantages regarding service and maintenance as well as initial costs by combining intrinsic safety, increased safety, and flame proofing explosion protection methods. The practical example of the Degussa Rheinfelden plant demonstrates how an operating plant can be revamped using remote I/O without loss of production. The Task The automation sections of the Degussa production plants were to be modernized using the Siemens process control system Simatic PCS7. The plant refurbishment was to take place over a period of just two to three weeks without interrupting production. The processes mainly consist of synthesis, distillation, and mixing.  Section of a plant The technology currently used in these plants was to remain unchanged while the process control was to be modernized. The main challenge of the planned revamp was to conduct all these changes within a very short period of time. Stopping production any longer was totally unthinkable for economic reasons. The Solution It was decided that the existing signal conditioning interfaces should be replaced while the sensors and actuators on the pipes and vessels should remain unaffected. The Pepperl+Fuchs Remote I/O was ideally suited for the task:
In order to proceed with the plant revamp the existing junction boxes were carefully removed from their mounting positions to make room for the FB Remote I/O enclosures in Zone 1.  Junction boxes shown removed from their mounting  FB Remote I/O enclosure surrounded by junction boxes Once the FB Remote I/O enclosures were fitted their functionality was fully tested in connection with the new Siemens system. Every input and output was checked using Siemens PDM. As an alternative a class 2 master (e.g. PACTware) was ready to take over if required. After successfully testing the circuits the existing loops were transferred to the Remote I/O slave one by one. Afterwards it was possible to remove the old junction boxes. At the customer's request the standard FB Remote I/O stations were also able to offer a very practical solution to driving the existing Ex-d valves to EN 50018 [1]. FB Remote I/O being the only system in the market to mount drivers for high power loops immediately next to intrinsically safe modules to EN50020 [2] made it possible to arrive at a very compact GRP enclosure. There was enough space to mount a new kind of removable Ex-d fuses which can be removed in a running system without the need for a hot work permit. These protect the Ex-e (EN 50019 [3]) circuits needed for the Ex-d valves. This was of course completely in accordance with the mounting regulations laid down in IEC 60079-14[4].  FB Remote I/O Sation with Ex e and Ex I circuits  Detail of pluggable Ex d fuses Any non intrinsically safe signals required for electrical signals were connected to the LB Remote I/O Station in the control room. The corresponding I/O modules slot into a backplane which is mounted on a solid metal plate which in turn is snapped on to a DIN rail. The modules feature pluggable front connectors with cage clamp terminals the same as the ones for Zone 1. This allows you to add or remove individual loops during operation without disturbing others. A Profibus gateway supports up to 80 analog or 184 digital signals or any combination of different kinds of signals.  LB Remote I/O Station for electrical signals in the control room HART Communication adds new Dimension Remote I/O stations offer additional benefits at no extra cost. HART enabled field devices can be addressed from a central position in the control room via the standard Profibus. It is no longer necessary to connect them individually using a handheld communicator or wiring them to a HART multiplexer. The operating station can make use of the Siemens PDM configuration software or employ a separate FDT based software package (e.g. PACTware). The FDT concept creates an open system by providing the framework for software device descriptions of all the peripheral devices. That way they can be integrated into the digital control system or the programmable logic controller (DCS or PLC). In the same way that HART DDs open the functionality of the HART field devices to the master the DTMs (device type manager) are integrated into the engineering tool of the DCS system which employs FDT (field device tool). Thus the user is able to configure his HART field devices via Profibus. Second generation Remote I/O are capable of handling standard HART protocols. This gives DD based masters like Siemens PDM the opportunity to act as a class 2 master to address field devices or even route the HART signals through the class 1 master. Pepperl+Fuchs Remote I/O act as a HART modem in that they receive HART telegrammes from the class 2 master via Profibus acting as the operator station. They then superimpose the HART modulation on to the 20mA current of the transmitter power supply or the output isolator. In turn the reply from the field devices is sent back to the DCS via Profibus using "nested communication" (fig. 7). As all this happens in parallel to the normal synchronous data communication the regular control operation of the Profibus remains unaffected. Field devices which are supplied with DTMs of their own can now make use of the device specific HART parameters via Profibus on top of the generic HART functionality which field devices offer that do not come with DTMs. There are also conversion programmes available to turn EDDs (electronic device descriptions) into DTMs (device type manager).  Class 2 master communicating with HART field devices via PROFIBUS Summary Remote I/O simplifies the engineering efforts when modernizing plants with hazardous areas. Proven principles of explosion protection are employed in combination and put to good use to reduce costs. Increased safety loops become as easy to handle as intrinsically safe circuits while offering more energy to the field devices at the same time. The practical example shows an installation concept for hazardous areas which aims at reducing the cost of ownership not only in hardware but perhaps even more so through the use of HART communications and asset management. Plug-in modules for power loops add to this effect during the life cycle of a plant. Literature References
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