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TO CONTINUE our coverage of challenges faced by new technologies, particularly automation technologies and fieldbuses, another hurdle to their adoption are skid and modular-equipment manufacturers. This is a “double whammy” because most new facilities are no longer “stick built,” but are entirely modular, so end users often can’t benefit from digital field devices. The second half of the “whammy” is that fieldbuses are well suited to modular design and fabrication because they can be preconfigured in the shop, and then simply connected by one or two cables in the field to local “mini-junction boxes” in a tree or chickenfoot arrangement.
So, let’s review the impediments and some incentives for skid manufacturers to make changes in their packaged offerings. Many skid fabricators are less likely to change from traditional wiring to Foundation fieldbus due to unfamiliarity, increased cost, and perceived risk. Even after getting an EPC to jump on the bandwagon, not many are willing to take responsibility for the instrumentation wiring of skid packages (pre-built by fabricators). These segments need to be designed and devices selected. Allowing the skid fabricator freedom to layout segments may provide the best (lowest cost) solution for them, but not necessarily the best solution from an operations viewpoint. This is because operators need proper segregation of process equipment and appropriate segment loading, which requires engineering interaction with other engineering disciplines and perhaps the owner-operator. Consequently, EPCs aren’t always willing to design for the skid fabricator because this may mean they’ve taken responsibility or risk warranty from the skid manufacturer.
A project manager or production foreman sees value in getting the skid on site, and may have trouble seeing past the risk to the schedule of forcing the skid fabricator to change design to fieldbus. Of course, if the skid manufacturer already has the fieldbus design on hand this is a moot point.
Skid manufacturers can maintain lower costs because the core components of their offerings are very similar from project-to-project, and since the automation component isn’t a key part of the project, it changes even less than the modules or skids themselves. However, because the basic design remains relatively static, this automation design can also be done once, and then slightly modified only as required. Fieldbus technologies lend themselves to slight modifications with no impact to the inter-module connections because the instruments are all wired to the same home-run, twisted-pair cabling. Taking this potential expansion into consideration on the base design maximizes flexibility for the price of a short cable run and the instrument itself.
In addition, because all manufacturers must remain competitive, the instrumentation selected is often the simplest, lowest cost, or de facto industry standard device that can provide the required measurement signal. With multivariable fieldbus transmitters, the number of expensive field devices can actually be reduced, thus saving not only the price of the instrument but also the nozzle and related connections too.
Unfortunately, not many skid or module manufacturers have their own in-house automation team, and even fewer have staffs that understand how fieldbus systems are designed. This is because mechanical and process engineering are the bread-and-butter, core part of the business, while electrical and Instrumentation (E&I)) are simply needed to complete the package. Though there aren’t too many outside consultants available either, perhaps they could fill this gap?
As indicated above, because fieldbus systems use a trunk and spur or star-type configuration, the number of connections/cables that need to cross the module or skid boundaries, which are the trunks or home-run cables, are connected to the base of these branches to complete the network. If the manufacturer is presently offering some form of remote I/O, then they’re trying to take advantage of minimizing the home-run cable. However, as has been proven by the FURIOS study conducted by Adventis in Germany, fieldbus technologies are more economical than the remote I/O option.
Manufacturing skids with minimal field terminations also improves overall project quality because more assembly can be completed in a controlled shop environment, which also reduces projects’ installation costs. So, if you’re skid or modular assembly manufacturer, and want to differentiate yourself from the crowd, while making larger profits than your competitors, offering digital communications and fieldbus technology could be the ticket.
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ControlGlobal.com is exclusively dedicated to the global process automation market. We report on developing industry trends, illustrate successful industry applications, and update the basic skills and knowledge base that provide the profession's foundation.