Many automation engineers are coming face to face with real fieldbus applications for the first time.
Fieldbus (the use of digital communications networks for distributed instrumentation and control) is a wonderful technology with many benefits, but fieldbus installation requires some additional considerations over and above normal 4-20 mA projects. In this article, we will discuss some of those issues, and show you how to deal with them.
Choosing a “Fieldbus”
Don’t get hung up on which fieldbus to choose. Fieldbus is a generic term for a variety of communications protocols using various media, but all are simply a means to an end. What you want at the end of the project is a satisfactory and functional control system, and practically every installation
will use multiple fieldbuses to accomplish the many tasks required. For example, you may use FOUNDATION™ fieldbus in the process plant, DeviceNet for a PLC network, and PROFIdrive to run motor drives. Every DCS can easily integrate all these functional plant buses into the Ethernet-based control room bus.
In process control engineering, “fieldbus” normally means FOUNDATION fieldbus H1 (H1) or PROFIBUS PA (PA); both fieldbuses are perfectly adequate and widely used around the world in refineries and process plants as modern day enhancements to 4-20 mA, 2-wire devices. This article focuses on H1 and PA physical layer implementation.
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