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The fieldbus architecture lends itself to maintaining an orderly appearance to controller cabinets. Figure 3 below represents one of our typical conventionally wired control systems, and Figure 4 (below) is typical of fieldbus. This cabinet uses five bus I/O cards that communicate with approximately 200 I/O points.
Fieldbus Segment Design
The buses selected for our facility also fall into two distinct categories—a powered bus and an unpowered bus. The powered buses include Foundation fieldbus and AS-i bus. The unpowered buses include Profibus-DP and DeviceNet. The powered bus includes the communications and device power on the same wires.
|FIGURE 4: FIELDBUS VERSION|
| Fieldbus reduces the amount of space needed. |
The FTBs would house this short-circuit protection equipment for field devices of both powered buses, and we hoped to identify a common short-circuit device type that could be used for both Foundation fieldbus and AS-i. At the time of our detail design effort, Relcom offered its Spurguard for Foundation fieldbus. We’d also hoped to find something in a similar form factor for AS-i. At our request, Relcom designed and manufacturing a Spurguard for AS-i, which enabled our powered buses to have the same look and feel. Figure 6 below illustrates where he Relcom’s Spurguard devices are located.
Our project’s ultimate goal was to have the stick-built process equipment, which included vessels, transfer panels, and skid equipment using an identical segment design approach. This allowed us to develop segment design standards that were followed by our engineering design contractor for the stick-built process equipment and by the various skid vendors.
CRITERIA used for assessing the viability of fieldbuses include the following:
|About the Author|
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.